Here is the Accuphase again, but now playing back redbook material. For the uninitiated rebook means 44.1 kHz with a 16 bit depth.
The coolest feature for me is the display LCD. I like to use that as a quick and easy diagnostics tool when doing my Snakeoil development. One of the questions I often ask myself is - is the music I am streaming bit perfect? Don’t over think bit perfect for now as my motivation for this is testing the players in both bit perfect mode and modified mode.
If you are using Snakeoil OS right now as your music OS, you may have seen this in the hardware tab before. It tells you the sampling rate and bit depth of the datastream that is sent to your DAC or sound card.
In the above example, I know the data is 44.1 kHz with a bit depth of 16 bits. But a strange thing is happening with Squeezelite, when playing music, this panel is actually telling me the bit depth is 24 bits.
The first editions of Snakeoil actually used a custom copy of Squeezelite that is modified to open the audio card with the correct bit depth, and send the data with the correct word length. I have since reverted that chance because Accuphase is telling me the data is effectively 16 bits (i.e. 16 bit data with 8 bits of blanks), and I bet they are right!
This is a video of me clumsily try and adjust the volume control on my mobile. Look at how the bit depth change over time.
Why did the bit depth increase though?
As the sound wave hits the microphone, the movement of a internal membrane is translated into voltages. A loud sound results in a bigger movement of the membrane, resulting in a higher voltage. The same is happening in reverse with softer sounds - smaller movement translates to a smaller voltage. This voltage reading (done 44100 times every second) is the basis for digital audio.
As the volume gets softer and softer, there comes a point when the small value can no longer fit into 16 bits of space (i.e. in 16 bits, even the least significant bit is now louder than the volume you want). When it passes this threshold, computer software does some clever things and extrapolate the volume into additional bits of space. By using 24 addressing it is now possible to represent that smaller number, and 32 bit space allows you go even smaller. This is why the display changes from 16 (full volume) to 24 (slightly softer volume), to 32 (very low volume), and ultimately to 0 (no volume).
And the display changes in real time, with < 1 second of latency. How cool is that huh? Do not forget this is a audiophile component we are talking about here!
Now I have something else that I can use to independently verify with what I can see from the Linux OS. If Snakeoil is my full time job, can I tax deduct the Accuphase DC-37 because it is work related?