By the way, here are some tests using the volume knob vs attenuating in digital domain.
When attenuating the digital input by few dBs, we inevitably reduce the resolution of the DAC (say the SINAD) by the same. When using a volume control post-DAC, this might not be the case, so let's try to compare what the D200 can achieve.
First, this a 1kHz @0dBFS (Full Scale) when the D200 is set to its max output, and that is 5Vrms (balanced outputs):
View attachment 495889
Unfortunately, at this high 5Vrms output, I can't reduce the headroom of my ADC for better precision (it is preceded by a scaler, of which next step is +6dB), meaning the D200 should achieve 19bits without that measurement limitation.
Now, if I reduce the volume by -1.5dB, I get 4.2Vrms output, and so I can increase the gain of my scaler to get the ADC in a its highest precision range:
View attachment 495892
Let's compare if I send a digital signal attenuated by -1.5dB and let the Volume at 0dB:
View attachment 495893
This exactly the same result.
Now, let's do the same at higher attenuation, for instance -6dB, which brings the output down to 2.5Vrms. The below is the comparison between doing it in digital domain (left view) versus with volume control (which acts after the DAC, as explained before):
View attachment 495895
This time we have a difference. Decreasing the digital volume slightly decreased the SINAD by nearly 3dB while it remained the same when attenuating with the Volume knob.
Let's try lower, @-12dB, therefore 1.25Vrms output:
View attachment 495897
The difference is now significative. In tems of SINAD and therefore ENOB, we loose more than 1bit of resolution when decreasing the output digitally, compared to using the volume knob. This means that the volume control of the D200 is very precise and ensures minimum loss. It is to be preferred if you need to attenuate the output of this DAC.
