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severegladiatorcrusade · 7 years ago

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The Value Proposition in Computer Audio: Entering Multichannel at the Ground Floor

THE VALUE PROPOSITION IN COMPUTER AUDIO

Entering Multichannel at the Ground Floor

“Mommy, where does stereo come from?”

Every audiophile should start each day with a thank-you to Harvey Fletcher and his dummy (whose name was Oscar and who had a microphone in each ear). Fletcher is widely known as the father of stereophonic sound. He first described what he called “auditory perspective” in sound in the early 1930s, later coining the term “stereo”. He won a posthumous Grammy in 2016 for his technical contributions to the recording arts. It was Fletcher, along with his collaborator Wilden Munson, who published the 1933 paper Loudness, its definition, measurement and calculation in the Journal of the Acoustical Society of America that established and quantified the concept of frequency-dependent hearing sensitivity in humans (and spawned the “loudness” button, but don’t blame Fletcher for that).

As Director of Research at Bell Labs, he opened the eyes and ears of the world to the potential of recorded music to unfold before the listener, by using multiple sound sources in separate channels to create sonic images with spatial location and directionality. He partnered with Leopold Stokowski and the Philadelphia Orchestra to prove his concepts and demonstrate their value. As part of this effort, he was responsible for the first direct stereo transmission (by phone lines from Philly to DC) in 1933 and the first stereo recording in 1940. His Bell Labs research team installed recording equipment of their own design in the basement of Philly’s Academy of Music. Fletcher oversaw over 100 stereo recordings and developed groundbreaking equipment to “enhance” recorded sound during playback.

IS MORE ALWAYS BETTER?

We audiophiles all enjoy Fletcher’s genius every time we drop the needle, put a disc in the tray, click the icon, or ask Alexa to tell our favorite streaming service to play a tune. And for most of us (including me, until I decided to write this article), two channels is enough. Given what many of us have traditionally spent on our stereo rigs, the idea of a 3 to 4 fold increase in spend and space requirements was simply not a consideration.

The only multichannel audio experience most audiophiles have had until recently has been through home theater, and most HT systems have historically not been well respected for serious audio. Twenty years ago in Stereophile, Chip Stern expressed the question that many of us were already asking:

“In a rollout of new technologies more or less driven by the expectations of the home-theater crowd, what's in it for us music-lovers?”

And in his review of the Toshiba SD9200 DVD player, he summed it up clearly:

“The Toshiba SD-9200 performed admirably, and offered a good level of audiophile two-channel performance for the price [emphasis added by me]; I trust that what it offers in the way of multichannel panache might put it over the top for some viewer-listeners, but I'll have to leave that conclusion to those colleagues of mine blessed with true surround-sound setups.”

His laissez faire attitude notwithstanding, he damned the audio performance of home theater equipment with the faint praise of “for the price” but did not describe the performance sacrifices made to have more channels for the money. I’ll try to be more specific in this work.

[ENTER THOSE EXPERTS, SOUNDSTAGE LEFT REAR]

It was only through the ears and pen of early devotees like @Kal Rubinson that we were exposed to the potential of multichannel audio for audiophiles. He wrote this about Willie Nelson’s instrumental version of Night and Day in his own review of the same Toshiba SD9200:

“I'll spare you the stereo/surround comparison...Right from the first notes, the multichannel version sounds incredibly live...I sense the ambiance instantly, and every sound is realistic and credible”.

And here’s his summary of the MC Buena Vista Social Club (World Circuit/Nonesuch 79478-9) from the same review:

“Listening to the DVD-A's stereo track... was...satisfying, but when I switched over to the Surround track (not a simple task, under the circumstances), I wanted never to go back.”

His reviews of the day also documented the rigors of MC audio, e.g. “The user interfaces (read: controls and menus) of multichannel components are complex and, um, idiosyncratic”. Worse, source material was not common and came in multiple formats each of which was more expensive than the last. I’ll spare you a complete history of multichannel audio and leave these links for your use if you want to learn a bit more: MC history , mp3 5.1 (!) , MC history according to Dolby , and Surround Sound: the Audio Side of Home Theater.

I’ll also spare you the history of MC equipment for audio. To date, the good stuff has come dear. Almost all of the affordable home theater systems from major electronics producers have been classic, mass market, consumer-level products designed and best suited for watching football games and movies. There are a few HT gems worth the effort it will take to find them, and there are now some excellent and affordable HT receivers that do audio very well. HT is one source of value in MC audio, and if you’re careful and selective in your choices of equipment you can get some fine MC sound for very little money. More about that in a bit.

THE WINDS OF CHANGE

What’s gone is gone and what’s done is done. MC audio just ain’t your father’s home theater any more. I’ve had a HT setup for almost 20 years, with a ceiling mounted projector and a series of receivers and speakers in the house. I started with one of those $200 loss leader HT systems that included a receiver and a small 5.1 speaker setup, just to see what it was all about. We loved the 8’-plus image, but the audio was just not suitable for serious listening. I upgraded each time my projector bulb died, because it was almost as cheap to buy a new projector as it was to replace the bulb back then. And, of course, what’s a better projector without better sound? So I ended up with a pretty nice Pioneer Elite 7.1 receiver with decent DACs (24/192, Burr Brown as I recall) that sound quite fine.

While researching my next pieces on Raspberry Pi and other SBCs, I discovered a 6 in / 8 out DAC HAT for the Pi for $58 that screamed “BUY ME!”. So I thought I’d get one for inclusion in an article on advanced stuff that audiophiles can make and do with a Pi, and I put it in the queue. After getting the article on modifying the Pi for higher performance to Chris, I started working on the next piece. After building a DAW on a rodded 4 gig Pi 4, a few Pi based NASes with different software, a freestanding wireless hub, and an active crossover, I started working with the Octo and had such a great time with MC on the cheap that I decided it deserved its own article. So you’ll read about the other projects in a future article.

FOR ME, MORE IS BETTER ONLY IF WELL AND PROPERLY DONE

When I fired up the first track on the first MC system I set up as part of my research and testing for this article, I had the same experience Kal described: right from the first notes, the multichannel version sounds incredibly live. It was truly eye opening to hear a Mozart Violin Concerto (24/96 flac) played by Marianne Thorsen in 6 channels on decent equipment. I don’t wanna go back to stereo, Mom!

Good MC really is that good. I don’t think I’d have gone for it when it meant doubling or trebling my investment in hardware, even if I’d had the same epiphany 20 years ago. The really good news is that you no longer have to spend your retirement fund to achieve it. There’s now a value based approach to multichannel that converted me in a fraction of a second, once I got it up and running – and that’s what this article is about. The heart of my value-based MC system is a Raspberry Pi, but there are options.

It should be obvious that a truly top quality 4 channel system will be close to twice the cost of a stereo rig of equal quality. For MC, you need as many speakers as you have channels plus enough amplification to power them all and cabling to connect everything. You also need either a MC DAC or a MC digital “splitter” (e.g. the MiniDSP U-DIO8) plus a pair of 2 channel DACs. If you like your current speakers, you’ll need at least 2 more just like them, along with an equal number of amplification channels as good as your stereo rig. And if you’re using a planned upgrade of your current stereo system to expensive stuff as a reason to look at MC, you really want to be sure you love it enough to double or triple up.

So here’s an entry level approach to multichannel audio for the cautious, the curious, the impecunious, the miserly, the skeptical, and/or the value minded audiophile. We’re not talking about state of the art MC audio here. We’re talking about decent sound quality from good basic components that most of us could enjoy in a second or third system, and that more than a few might even use as their only one. This approach will give you a good idea of the capability of MC and whether or not it’s for you. If you decide it’s not, you’ll have a few good and inexpensive little components to resell or repurpose. You can also add a MC interface (e.g. MiniDSP UDIO-8), another DAC and some good inexpensive powered speakers to your current 2 channel system to experience the power and beauty of MC before committing to more expense. Ideas for all of these components will be discussed in a little while.

Instead of a splitter and multiple DACs or a MC DAC, you can use a 4+ out digital audio interface sold for musicians and recording. Earlier DAIs with USB connectivity had duplex USB audio, too – but the current generation is different. On most current models, USB connectivity is limited to power and data exchange with the host computer, and digital I/O is limited to S/PDIF, AES and ADAT. This makes a DAI a less desirable option for many and unusable with a Raspberry Pi unless you add a HAT or other device to provide usable output to the DAI. The other practical limitation on value-based MC is resolution – I haven’t found an entry level MC DAC or DAI that would let you go above 24/192. Many of us listen at or below 24/192 anyway, and it’s certainly good enough to demo the MC concept for you. Doing high res MC requires equipment far more costly than a Pi and an Octo HAT, although improvements in basic SQ of the equipment (independent of source material and format) are often not as dramatic as the associated increase in cost might suggest they should be.

You can get MC sound quality fine enough to please most of us, and certainly fine enough to give skeptics an idea of the potential of MC in a 4 or 5.1 system, for under $1000 complete. Those who love the concept but want better stuff after hearing what you can do for under $1k can easily go as far upscale as desired. Having spent less on a “demo” system than they did for a connecting or power cable, they can use the mule as an extra system, sell it, or give it to a friend or relative with less money and/or less critical taste. So let’s get into the alternatives for what to play, what to play it with, and what to play it through.

SOURCE MATERIAL

MC audio most often used to mean synthesized ambience, because there simply wasn’t much well recorded, high quality program material in native MC formats. But high quality source material from most genres is readily available now in formats we all use daily. You can buy MC from half a dozen fine online vendors as 24/48 and 24/96 flacs, DSD, SACD etc. The gimmicky “surround sound” formats of the past no longer plague us, and MC is just a vehicle to more realistic presentation. Past formats either manipulated 2 channel recordings or used multiple recorded channels to dazzle the listener with sounds that bounced around the room. Audiophiles had no use for these gimmicks.

Today’s synthesized MC is done in your player software and is much much better than the old approaches. Good players like JRiver Media Center and Roon offer multiple output formats for 2 channel sources, and they sound pretty fine. You can get similar flexibility from some of the open source players too, although many require a bit more work to set the output format if you’re running Linux, by making you edit one or more configuration files. Still, instructions and guides are readily available on the web. As with any anonymous advice and (especially) code or command lines, make sure that any advice you take from the web has an authoritative source. I play it safe by first trying things on a canary in the mine – a development computer with no network or internet connection at all.

There are also many fairly high quality videos of great live performances in all genres, available in a number of proprietary formats (some of which require decoders). The most readily available video sound evolved from early Dolby 4 channel in ‘82 to 5.1 in ‘83, Pro Logic in ‘87, DTS in ‘93, 7.1 in ‘07, then Atmos with speakers in the ceiling and finally to 9.1 and beyond. How many channels you “need” is up to you, and MC experts may disagree - but I think that 4 (plus a sub if your main systems don’t sufficiently shiver your timbers) is enough to understand what MC can do for your music. You can also extract audio from videos with a variety of software, e.g. VLC (easy and excellent).

Good music management software like JRiver, Roon etc lets you select your output format from many alternatives. It lets you do a decent job of converting input formats to your desired output format, including 2 channel sources to 4, 5, 6 or more. And several of the open source players rival this flexibility in much simpler packages. If used on an SBC like a Pi, there are functional limits set by processing power, bus speeds, available I/O routes, limited RAM etc. But you can tweak your resource allocation to play MC flacs as long as you don’t also add heavy demands with DSP, GUI, and system tasks & processes that are not associated with audio. We’ll discuss optimizing your SBC for this in a while. I’m listening to an excellent 6 channel 24/96 file right now from a Pi 3B+ with full JRiver Media Center GUI up and running, and the little bugger’s not even breaking a sweat. Below and to the right is the real time performance readout. As you can see, the CPU’s just breezin’ along with the breeze at a very comfortable 41.9C and the music is playing without a pop, crackle, stutter or audible anomaly of any kind. Even the JRiver GUI is working smoothly, if a bit slower than ideal, when browsing the library while listening. This is pretty impressive performance from a $50 device!

THE MUSIC PLAYER

Players that do MC are readily available. Almost all of us already use at least one player that will do it if asked politely. As this series focuses on value in audio (like the crusty old retired audiophile writing it), I’m only discussing open source software and inexpensive proprietary products that deliver the most bang for the buck.

For those of you who already have Roon & / or JRiver Media Center, they both do MC very well out of the box - either is a great choice. I’ve had some trouble with Roon through the OctoPi, which is the renderer / player / DAC I built for $100 around a Raspberry Pi 3B+ and an Octo ADC/DAC HAT. It’s the featured project in this article, to be discussed in a bit. With Roon driving the Octo, I can’t get sound from channels 3-8, no matter what I’ve tried so far. As my Roon plays MC fine from other players on multiple platforms and by HDMI to my 7.1 receiver, I must have set something wrong to cause the problem. JRiver plays MC perfectly through the same OctoPi, and all output formats are correctly enabled and played.

If you don’t want to spend $ for a music management system like Roon or JRiver, you have many excellent choices of open source software that will play MC music for you. On Linux, you can’t go wrong with DeaDBeeF – it plays MC in many formats, sounds great on properly set up machines, and does a decent job of tagging, library management, and display.

THE HARDWARE

THE SoC APPROACH

I’ve been looking for a path to MC for music playback with acceptable SQ at a reasonable cost for many years. For most of us, the biggest barrier to entry into the world of many channels has been the cost of the equipment, which (for a “component” digital system) is roughly proportional to the number of channels. But finally, in addition to a few HT-based approaches that let you experience MC audio with HT hardware you may already have, there’s a pretty good value-based approach using a 6 in-8 out Pi HAT DAC (called the Octo) of which most - including me, until a few months ago- have never heard. When I started this project, the Pi 4 was not ready for plug and play use with an Octo, so this article is based on use of a Pi3B+. I finally got full function with the Octo on a 4, and it does more, better and faster than the 3B+. It doesn’t sound any better until processing demands exceed the limits of a 3B+. The SQ of the 3B+ degrades at performance levels far below the 4’s limit.

Both the Zero and the 3B+ support 5.1 / 7.1 PCM to 96kHz, and 4.0 PCM to 192kHz. I wouldn’t expect too much from a Zero beyond stereo 24/192 flacs. And if you want the best SQ from a Zero, especially at greater than Redbook resolution, it can’t be doing anything except playing your sound files to a DAC via OTG USB while on your WLAN to access them from NAS. I suppose you could also get on your network with a USB adapter and use Wifi to stream, but this seems a bit excessive when the object of your affection and interest is a $10 SBC with finite limits on its performance. It’s possible to boot a Zero from USB / OTG using any of a number of tricks you can find on the web. But the USB bus has a limited bandwidth and SQ will suffer if you try to run everything through it in both directions at the same time. You can use a Zero for MC via HDMI – Roon bridge does MC well this way (more on this a bit further down the page).

Neither a Zero nor a 3B+ will bitstream or pass-through Dolby HD or DTS HD. A 4B will play 192k 7.1 PCM. You can decode Dolby HD and DTS HD to these limits. Other MC formats are also supported but most require downsampling. The Pis do support lossy DD/DTS bitstreaming, but DD+ needs to be decoded to PCM or transcoded to DD. Asking any Pi but a 4B to play HD video with a high res multichannel HD soundtrack is pushing your luck.

So the bulk of this project centers around a fan cooled Pi 3B+ with heat sinks and zram, set to its maximum CPU rate and minimum GPU RAM usage (set memory split to minimum under advanced options / memory split in raspi-config). It boots and runs from a USB SSD (240 gig Inland Pro in a Savent housing), which I recommend for most audiophiles. Boot and general response are much faster than from an SD card, and it really helps the JRiver GUI behave like it does on a “real” computer (but don’t tell your Pi I said that – they’re tired of being picked on because of their size!).

Inland is the “house brand” at Microcenter and readily available from others like Amazon. I’ve avoided their prior products because they had measurable performance handicaps when compared to the slightly more expensive brand name alternatives. But the Pro series of SSDs was both cheap enough and well enough reviewed to justify a deeper look. These are apparently made by Phison, a 20 year old Taiwanese company that makes the innards of more than a few well respected brands (which are actually rebrands). Tucked into a $10 USB3 adapter case, this is a great way to get your feet wet with a serious Pi project (or anything else that requires a small SSD). I’m running one on the USB port of my ASUSTOR NAS for the ROON database, & it’s been excellent in continuous use for several months.

THE DAC

Enter the Octo, a 6 in / 8 out Pi HAT ADC/DAC that plays up to 24/96, and costs $58. That’s not a typo and you read it right - FIFTY EIGHT DOLLARS for a 6 in / 8 out 24/96 ADC/DAC complete with separate RCA breakout boards for ins and outs. It’s a Raspberry Pi HAT (Hardware Attached on Top) that connects via the large (40 pin) GPIO on top.

A WORD TO THE TECHNICALLY TIMID: At first glance, it looks as though there is zero support for this device when you buy it. There is absolutely nothing in the package except the board, the standoffs, the breakout boards, and the small ribbon cables that connect them to the main board. There is no contact information. There are no markings on the boxes. Multiple Amazon reviews complain about a lack of support and being on your own if you have a problem. THIS IS SIMPLY NOT THE CASE – you just have to do a little web searching to find both community support and the person behind Octo.

The creator of the Octo is a very nice, knowledgeable and responsive guy named Matt Flax (screen name Flatmax), who lives in Sydney. He’s interested in, supportive of, and responsive to input from users of his creations (Octo’s not his only product). This is his github page and this is his DIYAudio forum. It seems clear that he’s either not trying to build a business around his inventions or he’s woefully inept at marketing and branding…..or both. But he’s definitely there for you if you reach out to him – he just hasn’t provided any channels for customer relationship management.

But support it he does – in spades. For example, it wasn’t obvious to me in what order he had the RCA jacks set up, and there are a few “standards” around the world for channel order (e.g. SMPTE 5.1 is L-R-C-SUB-LR-RR and FILM 5.1 is L-C-R-SUB-LR-RR). So I contacted him with a PM through DIYAudio, and he got back to me within hours. He explained that even though installation seems to configure ALSA for you, it still leaves all options to configure the I/O order as you wish.

SO – ON TO MAKING A MULTICHANNEL MUSIC MACHINE FROM A Pi AND AN OCTO

The first decision is how to house the thing. If you choose not to use a cooled case for the Pi, you can just insert the Octo directly into the GPIO receptacle and use the provided standoffs to support the free end of the board. You can use this assembly exactly as pictured below, if you’re willing to live with a pile of pieces held together by wires. I’d put some insulating feet at the bottom corners if you do this. And with all the conductive spots exposed, an errant wire or metal object could fry everything.

I was unable to find any commercial case that would hold the Pi with its HAT on, except for flimsy Pi bottoms that don’t really protect any part of it from any practical dangers. If you want a case, you’ll have to make one like I did. You can build a single container from scratch to hold the Pi, the Octo, and the connector boards. Or you can build a separate case for the Octo and breakouts, connecting it to the Pi in a cooled case with a ribbon extender. If you go this route, you can power the case fan(s) from the appropriate pins on the GPIO (second and third from the left in the outer row seen in the picture above) by extending the fan wires to be as long as the GPIO ribbon jumper.

Unless you plan to leave the OctoPi in a protected area and never fiddle with it, you should at least cobble up some kind of case or mounting system for the breakout boards if you want to be able to use this like any other audio component. I strongly doubt that there will ever be a commercially available case for the thing because demand can’t possibly be strong enough.

A WORD TO THE WISE: do not assume that the GPIO ribbon cable will automatically connect pin 1 to pin 1. It is not keyed to the header on the Pi and it is not keyed to the pins on the Octo, so you can connect it backwards at either end. Doing so puts a voltage drop across pins that connect to parts unable to handle it, resulting in smoke, smell, and shame – and ya’ gotta buy another Octo :(

If you use it as pictured above, it’s physically supported by the GPIO header plus a pair of nylon standoffs that come with it. I was unable to find a fan cooled case that would hold it this way, and I wanted to be able to use it on multiple SBCs without having to disassemble everything each time. I also wanted a permanent mounting place for the 14 RCA jacks through which it passes analog audio in and out, to facilitate experimenting with DACs, Bluetooth, analytical tools etc. And a case looks right.

So I “borrowed” my wife’s old acrylic recipe box, made a few modifications, and connected the two boards with a 40 pin ribbon cable long enough to let me keep the Pi on top of the breakout box.

Again, I did this project first with a 3B+ because when I began it there were several web reports of failure when used with a 4. I felt obligated to duplicate this out of a sense of duty to the AS community, and my first attempts were indeed met with failure. I also used the 32 bit version of Raspberry Pi OS, because the earliest versions of the 64 bit version were not completely & properly configured for audio and were not easily updated and completed. Updates have been made since the first version, but it’s still not fully functional and ready for audiophiles. So this project is built on the 32 bit Raspberry Pi OS on both 3 and 4. I’ll have a go at the 64 bit version again in a few months.

Although assembly is easy, it takes a little effort to get this up and running. It’s not difficult if you follow the clear instructions found HERE (https://github.com/Audio-Injector/Octo). The procedure is simple:

Download this package to your Pi:

Install the Octo card from the command line with this:

Remove PulseAudio because it can interfere with Octo function; enter this into the terminal:

Reboot and the Octo should show up with all 6 in and all 8 out available to any audio program

You can configure channel lineup at the RCA outs in ALSA, but the defaults work fine for me with JRiver Media Center.

https://github.com/Audio-Injector/Octo/raw/master/audioinjector.octo.setup_0.4_all.deb

sudo dpkg -i Downloads/audioinjector.octo.setup_0.4_all.deb

sudo apt remove pulseaudio

I’ve used every output format option from 2 channel to 7.1 with success

Once it’s installed, just connect the appropriate RCA outputs to your DAC, powered monitors etc and listen away. I’ve had great success with JRiver Media Center, VLC, and a few other such players. Interestingly, I can only get Roon Bridge to work on this with 2 channel output into RCAs 1 and 2. When I go to any MC output format in Roon, there’s either silence or electrical noise from all the RCAs except 1 and 2. I’ve tried everything from editing asoundrc or asound.conf to using card-specific configuration in /usr/share/alsa/cards/<card_name>.conf – and I’ve failed each time. If I figure this out, I’ll post the solution. Searching the Roon database and the community forum finds nothing. This and this are two web pages on configuring ALSA for multichannel use. Neither helped with this.

SO HOW DOES IT SOUND???

All the following observations were made running JRiver Media Center on the Pi, further verified with VLC and Kodi on the same Pi. Remember that the Octo will only go to 24/96, does not do DSD etc, and is a primitive device compared to the current state of the art.

In two words, it sounds very good. It’s a better DAC than almost any I’ve encountered on a consumer mobo or SoC. As I’ll detail below, it’s not quite up to my iFi Nano DSD or my Emotiva Stealth in head to head SQ comparison. But it sounds good enough to serve most of us in a second system or system in a second location. I’ve been using it for a few days at a time over the last 2 months or so for daily 2 channel listening, and I’d have few serious regrets if I had to use it as my only system.

Brian Bronmberg’s bass on Wood is tight enough, although it’s not quite as rich and punchy as it is from a Pi 4 into my iFi. Marianne Thorsen’s Mozart Violin Concerto #4 (5.1 24/96 FLAC) sounds excellent, with only a bit of “haze” flattening its impact a tiny bit compared to my better DACs. Her violin is properly left of center fronting classically positioned and spatially (as well as tonally) accurate sections in a surprisingly intimate playback. This is an outstanding recording that I highly recommend – and I‘m not alone. Kal Rubinson named this an album to die for in the February 2008 Stereophile.

Christian Grøvlen’s piano version of Bach’s Chromatic Fantasia and Fugue in D Minor is a fine example of what 5.1 does for solo piano. The Octopi presents a well sized piano image with balanced tone and a realistically unfocused distribution of highs and lows. When you listen to a real piano in person, you don’t get the left hand from the left speaker and the right hand from the right. Whether open, partially open, or closed, there’s little frequency specific directionality and the piano doesn’t sound like it’s exactly as wide as the space between your speakers. This is even true when you face the pianist’s back, which is almost never done in real life regardless of the genre or venue.

The Octopi puts Grøvlen’s piano in front of and normal to you, as it would be in concert. You’re surrounded by the sonic ambience of a real Steinway grand in a small church. Mixing it down to 2 channels and comparing it to my reference system, I find the sound quality to be a bit behind my SMSL SU-8 v2 driven by Roon Bridge on a Pi 4 playing through my Prima Luna power amp and Focal towers. As I found with Bromberg’s bass, the bottom’s not quite as big and moving as it is on better 2 channel DACs. The sound stage lacks a little depth in comparison, and subtleties like delicate cymbal and brush work are a bit less clear and distinct (especially with the volume way down). But this is a wonderful recording that’s offered up intact by the OctoPi – it’s a joy to hear.

I’ve listened to many 2 channel files as well, to see how comfortable I am with the OctoPi as an everyday player. I like Joni Mitchell’s Hissing of Summer Lawns both as music and as a test of audio fidelity. Critics have panned it as unimaginative, bland, formulaic, etc – but I disagree. Listen to Robben Ford’s dobro playing on Don’t Interrupt the Sorrow and you have to appreciate how sweet the little Octo can play.

Joni’s voice is equal parts rich, inspiring, and depressing….as it’s supposed to be. The background singers are right there as well, even though I’m not convinced I could identify them all from blind listening with any DAC. For the record, you’re hearing James Taylor, David Crosby and Graham Nash! The Octo lets you hear the amazing close harmonies in Joni’s unorthodox, personal guitar tuning alterations. And Max Bennett’s beautifully tight, barky bass is clean and punchy on In France They Kiss on Main Street.

String sections have a bit of grain compared to better DACs. Reeds are closer to excellent, with only a little more reedy roughness than was there live in players like Paul Desmond and Art Pepper. Percussion is clean and solid, with lifelike fading of sizzle and crash cymbals, a palpable chunk chunk from the hi hat, and excellent delineation of different components of the set, e.g. 9x13 mounted toms from 16x16 floor toms. Snares have the right snap and brushes are not lost in the mix, especially the wiping shhhh of a good left hand during a ballad. You’ll also be bowled over by the combo of Joni playing Moog along withThe Warrior Drums of Burundi on The Jungle Line. With Jriver’s upmix to 5.1, this track is so big and alive it’s almost intimidating.

Further, although I never thought I’d go to the trouble of setting up a second system just for MC, the OctoPi now lives in my living room, sharing a shelf with my “good stuff”. It’s my dedicated MC front end, driving my Prima Luna power amp and Focal towers as front L&R (thanks to DACs with good remote control and multiple inputs). But more importantly, it’s good enough to bring you multichannel audio that lets you appreciate its charms. The first time I fired it up, I remembered Kal Rubinson’s statement from his Toshiba SD9200 review (quoted above): “Right from the first notes, the multichannel version sounds incredibly live... I sense the ambiance instantly, and every sound is realistic and credible”. Yes indeed!

LIMITATIONS

The Octo was designed and created to work with the 32 bit Raspberry Pi OS on a 3B+ or earlier Pi. It was not written for, tested on, or intended for use on a 4. With only a little work, I was able to eliminate the SD card and get it to boot and play on a 3B+ from a USB SSD (which I highly recommend). I have it working well on a 4 running from a 64G microSD card, but I still haven’t successfully moved the entire file system to an SSD and booted up a fully functional Octo4 without a card.

Once you install the Octo card on a Pi, most other functions are inaccessible. HDMI audio output cannot be used because the Octo configuration files limit any and all audio output to the Octo. Even if you disconnect the Octo card and want to use the Pi for anything else, you’ll have to reboot it with an OS and file system on a card or drive that’s not configured for the Octo. This is a simple matter of unplugging a USB SDD or removing the Octo-configured SD card and substituting the Pi OS image you want to run instead. But it’s one more step that many nontinkering audiophiles will find annoying.

I suspect it’s possible to make the Octo work with some of the audio software that comes with embedded JEOSs, eg Volumio, piCorePlayer (Tiny Core Linux), etc. I did not take the time to try to figure out how to make that happen, because I’d have to learn in detail what’s in each of those distros, how to load the Octo drivers, which conf files to edit and how, etc. If I find the time, I’ll try to get it to work with piCorePlayer and Volumio. But for now, I can only confirm how well it works on the latest 32 bit Raspberry Pi OS as of September 2, 2020.

Interestingly, it emits a mild click/pop when starting play from idle if directly wired to the output stage. At least in my setup, this is not loud enough to damage anything or be a major annoyance. But I suggest keeping your volume down the first time you start a track, as it may be sensitive to equipment. Interestingly, when I hooked it up to a pair of low latency BT transmitters for wireless 4 channel, that transient disappeared! And speaking of wireless MC……...

DIP YOUR TOES INTO WIRELESS MC WITH OCTOPI & THE LATEST BLUETOOTH

This is another topic on which I’m preparing a full review and discussion. But I can’t resist throwing it into this piece because it’s ideal for the OctoPi and it’s truly cool!

BT has a bad name among audiophiles, and historic experience suggests that it’s justified for most listening more critical than plain vanilla background music. But Bluetooth has come a long way, and the latest Qualcomm AptX codecs in the latest chips work really well within their design parameters. The limit on resolution in currently available devices is “only” 24/48, but the basic specs are impressive: THDN = -80dB, SNR=129 dB, and PEAQ = -0.05. If you’re unfamiliar with PEAQ, I’m working on a review of value-based audio quality measurement and assessment tools & methods, of which PEAQ is starting to appear in promotional material like Qualcomm’s AptX website. For now, I’ll just describe the 4 channel system I set up with the OctoPi and two pairs of adaptive low latency / HD BT transceivers. The HD codec does make a readily audible difference in clarity, definition, background silence, and dynamics – it’s clearly better and well worth buying new stuff to get it.

The critical piece of info here is that you have to be running the same codecs in both the transmitter and receiver to get the desired functions, e.g. low latency, HD. If they don’t match, you get the same old SBC Bluetooth codec that connects your phone to your earbuds. As I found out the hard way because the info was not provided by the manufacturer of the first pair I bought, very few of even the latest BT speakers use the most up to date codecs. You can’t split MC into stereo BT pairs with the latency of a standard BT system because it’s not consistent enough to avoid a subtle random “reverb” effect. Even the latency of the standard HD codec (lower than a standard BT at about 80 ms) is definitely audible if you hard wire the fronts and use BT for the rears, but the latency is sufficiently consistent from device to device in the same room with no barriers between transmitters and receivers to do fully BT MC from an Octo card into multiple DACs. This works OK with my iFi, Emotiva, SMSL, and M-Audio, although I cans ee how different DAC technology might affect synch in playback.

Here are the RainyB long range transceivers I bought to use as transmitters.

All of these units look pretty much alike regardless of manufacturer, and they may all come out of the same factory for all I know. I picked these because the specs are all the same, the Amazon reviews were very good, and they were only $42 compared to some that get close to $100. For the receiving end, I got a pair of $20 HD / LL transceivers that are much smaller because they have internal antennae (pictured below). Again, there are several similar products in that price range with the same specs. All the latest generation BT transceivers have optical I/O as well as line level analog via 1/8” TRS jacks. Most include a hair thin optical cable along with a pair of male RCA-to-male TRS 1/8” cables and a 1’ USB-C to USB-A cable for charging.

Pairing is no different from any other BT you’ve used, except that there’s no GUI to guide you – so it’s possible that you’ll pair one with another BT device within range if it’s also in pairing mode. To prevent this, I sat the two next to each other and activated pairing for both of them simultaneously. Because they have internal batteries, you can do this before moving one or both to the locations in which you want them to live. They also work with the charging cable plugged in, which is good because I hate having to remember to recharge audio device batteries.

Once paired, I used analog lines into the transmitters and optical out of the receivers to Edifier 1280s (which do have integral BT, but it’s not low latency). I was pleasantly surprised at the SQ, which is good enough to demonstrate the endearing qualities of MC and more than fine for casual listening in 2 channels or more. The analog link between DAC and BT transmitter is the weak one here – it’s not going to win Product of the Year in anybody’s book. Using low latency, with line of sight between BT device pairs, there’s no audible time shift between front and rear channels. I also set it up with optical into my SMSL SU-8 DAC driving a Prima Luna power amp and Focal towers in front and the Edifiers in the rear. With LL, there’s no audible delay and the sound is good enough to listen to (and maybe even to write home about).

I find a consistent flattening or slight dulling of the music through BT compared to directly connecting the DAC(s) to the analog inputs. It’s just not as alive, e.g. transients seem a bit slow. The latest AptX low latency and HD codecs both seem to reduce this effect a lot, making it tolerable for extended listening (which I don’t like to do on my old fashioned SBC BT headphones or with a Rocketfish BT receiver I bought years ago). I like the 4 channel setup enough to leave it assembled and ready for use, so I can listen to MC if I’m in the mood.

I haven’t tried using both long range transceivers to send and receive 2 channels to my best rig (Prima Luna / Focal) because I don’t have a computer or even a good DAC with an optical output, and using analog into the BT transmitter limits SQ enough to make it a nonstarter in my main systems.

THE BOTTOM LINE ON THE OCTO

It’s not going to become a Stereophile Class A pick. But mounted on a good Raspberry Pi, the Octo sound card will let you listen to pretty fine multichannel reproduction for a total outlay of about $100 for the entire front end. You’ll have 8 RCA line outputs to drive your amplifiers or powered speakers, so it’s easy to assemble your entry level MC system at very low cost.

You can even start with analog endpoints you may already have, although matched channels are obviously better. I put a series of patchwork systems together to see how they sounded. I mixed and matched Edifier R1280DBs, JBL LSR305s, and passive speakers (Rogers LS3/5a and Focal 726 Towers) powered by various electronics, to see how much the mismatch affected SQ. When upmixing 2 channel to MC formats, mismatched front and rear systems really doesn’t detract much from SQ if both are of high quality. On the best program material recorded as MC (e.g. the Marianne Thorsen Mozart Violin Concerti), better rears do make a difference in image stability, detail, and coherence of transients. But only with MC programs that were created for dramatic surround presentation does it really make a huge difference if the rears are identical or closely matched to the fronts. As most MC music is not intended to dazzle artificially, I’m living happily with my towers up front and the Edifiers bringing up the rear.

The Octo is a great way to get into MC for peanuts. I recommend this project highly for those to whom it appeals. But if the results I describe for this do not seem worth the effort and the Rube Goldberg nature of the equipment, read on – there are other paths to value in MC audio.

CONSIDER THE HOME THEATER RECEIVER FOR MULTICHANNEL AUDIO

I’m a big boy, so I’ll provoke a few flames and take the heat:

DISCLAIMER: I did not buy any new receivers for this project. I spent a fair amount of time listening to them, mostly at Best Buy. The BB we usually use has a big Magnolia “boutique” plus their standard stock. In addition to files on a USB drive, I brought my NuForce iCanDo so I could stream my own files over the web and have a digital source to drive the receivers.

BEGINNING WITH YOUR OLD HOME THEATER RECEIVER

If you’re sitting on a HT receiver that you no longer use, the path to MC begins in the closet where you store it. My trusty 10 year old Pioneer Elite VSX-30 receiver has been out of service for the almost 5 years since we retired and moved from our house to an apartment. We put a big, smart Samsung on the living room wall because I can’t mount our projector in the stressed concrete ceiling of our condo. I forgot all about the Elite until I was beginning my quest for MC knowledge and realized I had a decent receiver with which to experiment.

The down side of older and lower end current HT receivers is that I haven’t found one that would decode anything but wavs, mp3s, and wma files from its USB port. My Elite simply ignores FLACs, dsf, and other “good” files on a USB stick or drive, as does every other older model I could find in friends’ closets and other out of the way places. Another drawback is that many have marginal analog electronics. Their power amps have grossly inflated ratings and are simply nowhere near as powerful or clean as they’d like you to believe. And none that I could find has line level outputs for MC use. Even my Elite, which is far from a bargain basement piece, only has 2 channel line outs (“DVR” and 2nd zone), both of which are fixed level.

The up side is that the better ones actually sound very good. Many (like mine) have decent DAC chips in them and will play up to 24/192 very nicely when fed by a capable source through HDMI, coax, or optical inputs. This makes them ideally suited for use with a SBC (for which I prefer a Raspberry Pi to any other) or any streamer with optical or coax RCA outputs. And you can do MC audio nicely with any of these. You can also play DSD files if you convert to a format the internal DAC will play. Having a full feature remote is icing on the cake, and most of them do. Here’s my Elite playing a dsf file from JRMC on my Pi, downsampled to 32/192 (which I didn’t think the receiver would decode!):

You can buy a decent used VSX30 or similar model from Marantz, Denon, Sony, Yamaha etc for about $100-150. This is great value for a starter MC audio system – you can add a Raspberry Pi for $75, use an open source player like VLC, and have yourself a really nice system with the addition of as many passive speakers as you want and a sub. Start with something like Edifier P12s for $80 / pair (list price) and add a 100W Yamaha 8” sub for another $150. This totals under $500 for a 4 channel + sub system and about $660 for a full 7.1 that will make most of us pretty happy as an entrée into MC – and you can set it up for HT as well, if you’re so inclined. There are a lot of excellent HD music videos.

SQ is really good, especially for the price. And the magic of MC really does what Kal describes – it sounds incredibly live and lets you sense the ambiance instantly. Every sound is a bit more realistic and credible. By the time you get over the joy enough to listen for flaws in SQ, you’ll either love it as a second system used only for MC or be motivated to get good stuff and upgrade your main system to MC.

STARTING FROM SCRATCH WITH A HOME THEATER RECEIVER

A good, inexpensive new HT receiver is another path to multichannel value. Most entry level MC receivers are mass market fodder not well suited for audiophile use. The least expensive (~$300 & under) current models from Yamaha, Denon, Sony, Onkyo, Pioneer etc are marginal performers for pure audio, both in SQ and utility. So they have little appeal for us, e.g. many don’t play FLACs and they don’t do DSD. The nicest thing you can say about some of them is that they come with a polishing cloth. The entry level models also “only” play up to 6 channel (5.1) and do not decode theater MC schema like Atmos. This is irrelevant to most audiophiles, except that JRiver Media Center (and some other programs) will upmix your output to as many as 32 channels if you really want to do that. I don’t.

Because these devices are designed and sold for home theater use, the low hanging fruit on the feature tree is most attractive to video users. As the price goes above true entry level, the first things added are video enhancement (e.g. more HDMI inputs) and HT related features (e.g. more output power plus Atmos and other audio processing). For example, the entry level Sony MC receiver (STRDH590) features 145WPC in “5.2” format (2 RCA sub outs), decodes Dolby Pro Logic II, DTS 96/24, and Dolby Digital, and has 6 DSP modes with auto room correction. It does audiophile formats including DSD (although I couldn’t get a spec for the highest resolution and didn’t bring a DSD4 file with me). The one-step-above Sony (STRDH790) is a 145WPC 5.1.2 receiver with the same inputs. But this one processes DTS, DTS-HD Master Audio, DTS:X, Dolby Atmos, Dolby Digital, and Dolby TrueHD. It has one optical and one coax audio input, and will play from USB storage or your network. But the 2 added audio channels are in the ceiling and are only for Dolby Atmos – it’s still a 5.1 for audio.

If you go a wee bit upscale from the bottom tier, you can find a few fine sounding units for another $100-150. The Yamaha RXV-485 is an example of a decent $400 performer that will play 24/192 flacs and DSD4. It sounds very good, has some DSP, and is easy to use. With network connectivity, USB, BT, and a host of analog & digital I/O ports, it’ll digest whatever you can throw into it from a Rapsberry Pi to a serious network streamer. But you don’t even have to use a front end device with most HT receivers over $400 – you can stream to them from your NAS or plug in a USB drive and play your own files (once you’ve confirmed that the model of interest to you will recognize and play the formats of your choice).

You can also stream internet radio and streaming services on most HT receivers sold today above the $400 price point. You may have to spend $500 depending on the brand and model you like – but you can stream internet radio and streaming services and play MC along with all your usual 2 channel listening very nicely for the price of the receiver plus however many passive speakers yo need for your desired format. Be aware that you won’t find MC preamp outs at this level – that feature requires a bit more outlay, e.g. the $1000 Denon AVR-X3600H. And to be honest, it’s probably not an approach most of us would consider for a value driven MC audio system because you can get a decent 8 channel DAC for far less than that if you’re not satisfied with SQ from an OctoPi or need more flexibility than it can provide. I wouldn’t spend more than $500 on a new HT receiver for MC audio unless you also plan to use it for video or will use other functions. Some of the I/O and switching schema are quite impressive on the better receivers, with at least 4 HDMI inputs plus multiple coax, optical, and USB ports.

Another feature of value in a surprising number of HT receivers from cheap to costly is automatic room correction DSP. Many of these come with a calibrated mic and do an excellent job of normalizing in-room frequency response and phasing if you activate it. I haven’t seen any in which it was automatic or even default – you have to activate it if you want it. Even my 10 year old Elite has this feature, and it works pretty well.

OTHER ALTERNATIVES FOR VALUE BASED MC AUDIO

MC DACs

A MC DAC is no longer a dream and no longer priced out of reach for most of us. As you’ve now learned, the OctoPi is a true 6-in/8-out ADC/DAC with good SQ that brings the total cost of a MC front end to a whopping $100 with a 4 gig Pi 4. If you spring for an 8 gig Pi 4 because you’ll need that much RAM and don’t want to run from a USB SSD with ZRAM, you’re talking about $125. If you run from a small USB SSD, add another $30-$50. But, as I’ve already described, this is not highly flexible for playback – it does what it does, can only be used with a Pi, and limits other functions on that Pi while configured for the Octo. Fortunately, there are value based alternatives besides HT receivers if you don’t like or want to be bothered with an Octo and a Pi.

If you don’t want an HT receiver, the next step up from a Pi with an Octo card would have been a MiniDSP UDAC-8, a device well reviewed by many. Sadly, it was recently discontinued before I (or you) could buy one. However, the slack is being picked up rapidly. Consider the ESI Gigaport EX, a 24/192 8-out USB DAC for $125 that sounds so fine that I’m adding one to my own systems. It’s a really cool little piece about which I can learn nothing beyond its specs. I don’t know what’s inside, e.g. DAC chips, I haven’t bought one yet, and my wife says I should stop disassembling friends’ stuff without their permission. Soon I’ll have my own, but not soon enough to get a more thorough evaluation into this article. The ESI looks good and feels pretty solid even though it’s not metal. The case is made of what feels like pretty solid plastic material, and the connectors are typical board-mounted generic jacks with the same feel as a million other low to mid level electronic devices. Its use is growing rapidly both for live performance and in recording studios by many musicians and small studio owners who only need a few channels and can’t afford or don’t see the need for high dollar stuff. With a USB-C input, it’ll do up to 7.1 and is great for JRiver Media Center, Roon, and every other MC player I’ve tried. Just keep its 24/192 limitations in mind and you’ll be fine with it if it fits your plans.

Many of you know how much I love Emotiva products. With excellent quality, sound, and customer relations, they’ve always been one of my go-tos for anything they offer in my price range that I need. Their MC700 is an 8 channel DAC and control center for $700 list (and they have great sales from time to time). It offers 6 in / 2 out HDMI, plus coax, optical, and analog inputs. There is a USB3 port, but it’s only for their BT dongle (required for BT audio input). I haven’t heard this product, but after owning 2 prior Emotiva DACs and having a Stealth DC-1 now, I can confidently say that I really like the quality and neutrality of the Emotiva sonic signature in DACs. As I have no need for one, I won’t be buying an MC700 – but I encourage any of you to whom its feature set appeals to try one. Emotiva has a 30 day return policy that I’ve never had to use. But if their service is as good on that as it’s been when I needed them for other things, they’ll handle it promptly and gracefully.

There are other MC DACs and front ends at various price points, both internal and external with multiple connection options. You can choose from several designed for musicians, recording, gamers, and/or computer-based HT sound. For example, the $120 Creative Sound Baster X3 is a USB 7.1 DAC that goes to 32/192 & sounds very fine. It has unbalanced TRS 1/8” line out jacks, but it’s quiet (if you practice sound cable hygiene) and it acquits itself very well in a value-driven MC system. I personally think it’s a wee bit clearer, more alive, and more articulate than the Octo card when driven by the same Raspberry Pi. I do not find the 1/8” jacks to be a problem and could happily live with them – YMMV.

RECYCLING OTHER MULTICHANNEL AUDIO PROCESSORS

Devices like the Oppo 105 can be excellent MC DACs or complete front ends. The 105 and similar products contain network streamers and do internet radio & streaming very well. They’re no longer state of the art, but they’re still pretty good for dipping your toes into MC – and many of us could live happily with one of these as a front end in a second system dedicated to MC & HT. If your 105’s been gathering dust since you set up that new streamer, dig it out and try MC with it. With discrete line level outputs for 7.1, I think it sounds better than the OctoPi – it’s very clear, clean, articulate, and accurate.

Be careful about planned repurposing. Not all devices allow access to functions you’d think would be integral. For example, the Oppo BDP-95 (a predecessor to the 105 and a very nice device) does not provide direct access to the DAC. So you can’t use it as a stand-alone processor. But if your legacy device is usable as a MC DAC, you can use it to start exploring the joys of MC on the cheap.

AND LAST BUT NOT LEAST….MAKING MC RECORDINGS WITH THE OCTOPI

I’m preparing another article on Pi projects, featuring my mini-DAW. It’s based on a fully rodded and fan cooled Pi 3B+ because the Octo card wouldn’t work with the 4 when I first got it. And it’s amazingly capable, both with Audacity and with Ardour. Because real time monitoring requires the CPU to process the existing tracks for playback while processing the track(s) being added for recording, the 3B+ is not up to simultaneous monitoring and recording. The degradation in SQ is grossly apparent, with dropouts, crackling, and assorted pseudo-biologic noises on playback that suggest serious indigestion of the processing tract. As long as mic levels are set properly and you’ve done a thorough sound check before the program starts, real time monitoring (although the best way to assure the quality of the recording) is not strictly necessary. You do need to monitor the meters closely to be sure you’re not overloading any inputs when recording live music.

Sadly, the club in which we play is (like most other southeastern Pennsylvania clubs) still closed. So I couldn’t make any full length recordings to demo for you how well the little rig performs live. But I’ve made many MC recordings on it by laying down one track at a time in my home studio, using a click track to keep me on time because of the described inability to play recorded tracks in real time while adding more.

As I’ve posted on AS many times, I love ART equipment. They make wonderful products at great prices, and they represent true value for the audiophile as well as the musician and the recording engineer with a tight budget. That little tube preamp has XLR balanced I/O and sounds most excellent! Although crude, the bench version of my OctoPi DAW is fully functional and will do its job faithfully. Here’s the uncased DAW sitting on the iPad with inputs on the left and outputs on the right:

Here’s a shot of an Ardour MC session with 2 tracks recorded and #3 going in. You can see that the CPU is working fairly hard at 62% (the red usage widget in the lower right corner). But the temp is only 66 degrees and everything’s going perfectly well.

You can set Ardour preferences to route monitoring internally through the computer or through external hardware. Using internal processing is what makes the Pi choke. But using the latter setting and monitoring the track being recorded from its input, there’s no problem with SQ and latency is compensated by the recording program. Ardour and Audacity both do this very well, although it takes a bit of work to set Audacity up for this. Here are the instructions for latency correction in Audacity, to give you an idea of how easy or difficult you might find working with this program. Once it’s set for a given computer, it’s done and does not need to be changed unless you change hardware or software.

RIPPING WITH THE DAW

Remember that the Octo is an ADC as well as a DAC. So you can record directly into the RCA jacks from preamp out or any other line level analog sources. Although you could use any recording program you like, I prefer Audacity for ripping vinyl and CDs. It runs extremely well on a Pi 3B+ or 4. It’s an excellent program that rips to wav files. It lets you export and work with your recordings in any format and resolution you prefer (as long as the processor can handle it), which is not at all a problem for saving as Redbook files, even for MC rips. It won’t export to DSD or other serious formats, but you can capture the wav file at up to 384k. When exporting, you can convert to about 20 lossless formats, set FLAC bit depth and compression level, etc.

Here’s a minute of my rip of Dave Grusin’s Discovered Again (Sheffield Direct to Disc original vinyl, 1976, typical review HERE). This was ripped from my Thorens TD125 with fixed shell SME 3009, Audioquest cartridge, and Parasound Zphono USB directly to the OctoPi.

WAV File

FLAC File

If you’re interested in serious recording with a Pi, there’s also a balanced Octo card that’s either about to come out or already available (it was still beta when I last looked).

SUMMARY

Multichannel audio is cool, fun, and well worth exploring even if you have no desire or intent to adopt it. Many of you think you don’t want it but will change your minds within seconds of a first listen. The really great news is that you can apply what I’ve written here to set up an inexpensive MC system with sufficient SQ to amuse, amaze, and attract you into its lair. You can probably use some or all of what you have now. You can mix and match old and new components, and you can probably use the player(s) you love for MC formats.

I can’t believe how exciting good MC audio can be, and I urge you all to at least give it a whirl. The education alone is worth the effort – and I’ll bet that at least half of you get hooked firmly enough to keep a MC setup in use.

Stay safe and enjoy!!

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