I agree that it was hard for me to wrap my head around the various volume control issues. You hear things like "digital volume control is perfect because it is done in 32 bit" which is true in some aspects but not others.
The other issue that makes things difficult is that noise metrics for various equipment are quoted at very different levels, for example DAC SNR might be quoted at 2 V, 4 V or something even higher, at ASR amplifier SNR is measured at 5 W in to 4 ohms and full power, it makes understanding how these numbers come together somewhat difficult.
A few things helped me understand it better. One was playing around with digital volume control in a similar manner to that Roon volume control white paper and measuring noise digitally. This helped me understand that quantization noise is not really an issue, certainly a non-issue compared to the overall DAC / amplifier noise floor. The other was measuring actual noise level at my amplifier outputs with various DACs as this gave me a real feel for the ever constant noise floor of my system. And finally building a spreadsheet to calculate system noise levels based on DAC SNR, amplifier SNR, amplifier gain and amplifier power rating.
For example here is a plot from the spreadsheet showing system SNR as a function of volume position with 16 bit input data. Modeled parameters here are DAC SNR of 110 dB at 2 V full output (0 dBFS), amplifier SNR of 100 dB at 5 W in to 4 ohm, amplifier gain of 25.6 dB and full amplifier power of 125 W in to 8 ohm / 250 W in to 4 ohm. For reference this roughly models a MOTU Ultralite Mk5 and a Hypex NC252MP amplifier.
View attachment 190329
A few things to note, the plot doesn't go up to 0 dB because the amplifier will clip at volume positions above -2 dB. The high end of the graph is rather flat as the noise floor is limited by 16 bit input data at that point and not the DAC / amplifier noise floor.
For reference here is the same modeled system with 24 bit input data, as you can see although we are able to do better than 16 bit performance (96 dB SNR) we do not actually reach 24 bit performance (144 dB SNR) because we are limited by the DAC / amplifier noise floor.
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Michael