6 Critical Aspects of Digital Audio

So you’re looking into digital audio. Or you’re looking to improve your current digital audio setup. Either way, you’re going to need a couple of devices (or a multi-function device that plays more than on role).

Digital Audio Roles

There are 6 roles that must be covered to playback digital audio. They are:

ACQUIRE > STORE > CATALOG > CONTROL > PLAY > CONVERT

As far as which device(s) you need, well, there are a ton of options. At Musica Pristina, we believe it’s best to let the computer work be done by computer parts, and the audio work be done by audio parts. We’ll explain what we mean by first covering the “all-in-one” approach.

A device like a Mac Mini can cover all 6 of the digital audio roles. You can download an album you bought from HD Tracks, or rip a CD, and that covers “Acquire.” You then save it on an internal hard drive, call that “Store.” You tag it with album art and other metadata (artist, title, tracks, etc.) in iTunes, and that covers “Catalog.” You press play or fast forward or stop in iTunes, and that covers “Control.” The sound card in you Mac Mini does the actual playing, which converts stored audio data into a digital audio stream “Play.” And finally, the onboard DAC chip, which outputs to the headphone out jack handles “Convert.” So one device can perform all 6 functions… it just doesn’t sound very good.

Then “what’s best”, you ask?

There’s more than one good way and ultimately best is subjective. But, we do have a set of core beliefs that guide what we build. Maybe you share them with us?

First, Acquire and Store are not audiophile processes. So it’s best to leave those out of your audio equipment, and use computer parts for those functions. If you want access to a massive library of uncompressed music, a Tidal license lets you “rent” a ton of tracks for a small monthly fee. Alternatively, you can download tracks & albums (high res or not) from HD Tracks. Or you can rip CD’s that you’ve bought with any decent CD drive, even external USB connected drives are capable of accurately ripping the bits from a disc. Then, you can put this music on a network attached storage (NAS) device, which is essentially a set of hard drives with an Ethernet connection so the drives can be shared. Whether your renting your music, or storing it, it’s housed on drives, and available on your network over Ethernet.

Now, you need a piece of software to manage your library. Metadata is the term we use for all the “info” about your music. Album, artist, genre, tags, cover art, you name it. Most library / playback software provides some means of managing metadata. At one point, we even wrote our own.

But then they released Roon, and the game changed. Roon is an uber-sophisticated, but fun to use, tool to Catalog your library. It seeks out the metadata, and adds in things like reviews, related artists, lyrics and more. It’s easy to get the hang of, goes as deep as you want to go and most importantly, sounds amazing., More on that later.

You have to build playlists and press play on something, and Roon shines brighter than the rest when it comes to Controlling playback. For example, instead of letting the music stop when your playlist ends, Roon has a “Radio” feature that analyzes the types of material you’ve been listening to, and keeps the music going long after your playlist runs out. Sorting and filtering your albums or tracks feels more like playing, and less like building a spreadsheet.

Now that we have a list of tracks queued up, something has to turn stored audio data into something a DAC can convert. Stored Audio Data in, Digital Audio Signal out.

When computer audio started taking over digital (moving from CDs to Files), there were a few companies fighting to develop the standard output for connecting to a DAC. Unfortunately, as often happens in audio, “U”niversal beat performance. Every MAC and PC and Linux box has USB outputs, so just about every DAC made featured a USB input. For a long while, the ruling paradigm was to play a file on a computer and send the audio signal to a DAC over USB. We want to help change that.

I2S

When we set out to build a better player, we didn’t focus on USB. Instead, we focused on I2S (technically I-squared-S, or Inter-IC Sound) It’s a pure audio output, and the only input accepted by 99% of DAC chips on the market. It carries the clock signal and data on separate lines, instead of merged together. It’s simple, and elegant, and perfectly matches the signal it’s designed to carry. So why doesn’t every DAC have I2S? Many do, but it just isn’t “U”niversal. There is no formally agreed upon standard for transmitting I2S signals over long distances (like an external cable between a player and a DAC), so some manufacturers just don’t touch it. We think that’s a shame. Done well, it creates a holographic realism that we’ve never heard come through any USB connection on any device.

Musica Pristina offers two ways of listening to audio over I2S. Either with an A Cappella II and a Virtuoso PCM DAC, where the I2S signal is carried across an HDMI cable (Note: This is NOT an HDMI signal. It happens that the HDMI cable is a great means of carrying this signal. PS Audio and a few other manufacturers use this approach as well). Or with a Virtuoso Network DAC, which offers a built in Roon Ready Ethernet input. In either case, the Play portion of the chain mentioned above has one very simple task to perform: take an Audio Data Stream from the Ethernet input, and clock it to create an I2S audio signal to pipe into the DAC for conversion to analog. As a point of comparison, audio over USB requires the player to first process the Audio Data Stream into USB packets, then hand those to the USB controller to be send out on the wire, then the DAC needs to unpack the data, and ultimately re-clock it to feed an I2S signal to its internal DAC chips. As you can see, I2S can’t be avoided… but USB can be.

Finally, the I2S digital audio stream needs to be Converted to an analog signal that will be amplified to drive your speakers. We do this with dual Burr-Brown PCM 1794 chips. There are many chips that are more feature rich, allowing the end user to control volume, adjust filters and the like. We lean toward the purist side of the spectrum and prefer to convert to the analog realm as accurately as we can whatever it was that the recording engineer stored in digital. Give me an EQ, I prefer to set them all to zero, so to speak.

So here’s a quick recap of the 6 roles, and our suggestion for what to use where:

  1. ACQUIRE: We say get a Tidal account, download some great music from HD Tracks, or start ripping your CD library.
  2. STORE: NAS devices are the best. Many provide self-contained storage and backup solutions by using one or more redundant drives. Also, the Core part of Roon runs on QNAP and Synology NAS devices, so no need for another PC.
  3. CATALOG: Roon. We’ve yet to find a better tool.
  4. CONTROL: Roon. See #3.
  5. PLAY: A linear power regulated processor board that performs only one function: transform an Audio Data Stream (Ethernet) into an Digital Audio Signal (I2S) for conversion by a DAC. The A Cappella II does this. So does the Ethernet input of the Virtuoso Network DAC.
  6. CONVERT: A fully balanced, tube driven output stage, fed by DAC chips running in dual-mono that convert bits to analog, and nothing else. The Virtuoso PCM DAC and Virtuoso Network DAC are our recommendations here.

Roon’s RAAT Protocol (DSD, MQA & Audio Quality)

We mentioned above that we’d return to sound quality, and how Roon plays are part in that. The first way Roon does this is by format conversion. But wait, if we alter the bits we kill the sound, right? Not exactly. Most DSD capable DAC chips, for example, still convert to PCM prior to conversion to analog. Doing the conversion in the Roon Core instead, and sending native PCM to a native PCM chip (rather than sending DSD for conversion to a multi-purpose universal chip), sounds much better. If it didn’t, we’d have used a multi-purpose chip in our DAC instead. Roon can convert from DSD and MQA to PCM, enabling most DACs to play most material.

Perhaps the most important way that Roon makes our equipment sound better (besides making it more fun to use) is the Roon Advanced Audio Transport (RAAT) protocol. RAAT conveys a perfect (every bit in the right order guaranteed) signal to our devices, and leaves the clocking up to us. It does so over Ethernet, where an isolation transformer (this is part of the Ethernet spec) keeps the dirty PC side of things from physically touching the pristine audio components.

Musica Pristina is proud to have been one of the first Roon Ready devices on the market, and one of the very few audiophile grade Roon Ready devices available today. It’s evidence of our commitment to tracking down and implementing the best sounding audio components and protocols available today… and tomorrow.

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