i contacted eversolo trying to find out more about how they implement digital volume control , here is what the answered:
Digital Volume Control (DVC) achieves volume control by adjusting the amplitude of the digital audio signal instead of adjusting voltage through analog circuits. Digital volume is adjusted through registers inside the DAC. This adjustment process does not reduce the bit depth of the digital audio signal, as it only adjusts the amplitude of the signal without altering the original encoding of the signal.
In short, digital volume control does not result in a decrease in bit depth because it simply controls volume by modifying the amplitude of the digital audio signal rather than altering the signal's encoding. Therefore, even with volume adjustments, the integrity and quality of the digital audio signal remain unchanged.
Right, so they're right technically - but it's a little bit of semantics as the end result is still the same, which is a degradation of audio that is more pronounced the more attenuation you need to apply digitally. I mistakenly (like I guess many) thought it was bit rate reduction, but the net effect of using DVC on digital amplitude still reduces dynamic range and SNR, but 'techincally' yes.... it's not via a bit rate reduction.
End of the day, this is why they went to the expense and effort to do the resistor ladder volume in the A8.
I had to run it past ChatGPT to confirm something and got the answer I was looking for:
You:
does digital volume control in audio reduce the bit rate?
ChatGPT:
Digital volume control in audio typically does not directly reduce the bit rate of the audio signal itself. Bit rate refers to the amount of data processed per unit of time and is primarily affected by factors such as sample rate and bit depth.
When you adjust the volume digitally, what typically happens is that the digital audio signal is scaled up or down in amplitude before being converted to an analog signal for playback. This scaling process does not inherently reduce the bit rate because it doesn't involve removing any data from the audio signal.
However, there can be some indirect effects on perceived audio quality. If the volume is reduced significantly, the signal-to-noise ratio (SNR) can be adversely affected, resulting in audible quantization noise. This noise is a byproduct of the digital-to-analog conversion process, and while it doesn't directly reduce the bit rate, it can affect perceived audio quality, particularly at lower volume levels.
In some cases, digital volume control can also introduce distortion or artifacts, especially when reducing the volume, although modern audio processing techniques aim to minimize these effects.
Overall, while digital volume control doesn't directly reduce the bit rate of the audio signal, it can affect perceived audio quality in various ways.
You:
sounds strange. I thought a digital audio signal was 0's and 1's, and within that signal is the encoded audio samples, which dictate the volume for decoding. for example a 16 bit track has a maximum amplitude value of 65536, how does reducing the digital signal amplitude change what the dac ultimately decodes from the audio?
ChatGPT:
You're correct that a digital audio signal consists of a sequence of binary values representing audio samples. Each sample has a certain bit depth, which determines the resolution of the sample's amplitude. In a 16-bit audio system, as you mentioned, there are 65,536 possible amplitude levels.
When you adjust the volume digitally, you're essentially scaling the amplitude of each sample before it is converted from digital to analog form by the DAC (Digital-to-Analog Converter). This scaling process doesn't directly change the bit rate of the audio signal because the number of bits representing each sample remains the same.
However, reducing the amplitude digitally effectively reduces the dynamic range of the audio signal. Dynamic range refers to the difference between the loudest and softest sounds in the audio signal. If you reduce the volume digitally, you're essentially reducing the amplitude range within which the audio signal is encoded. This can result in a loss of detail, particularly in quieter parts of the audio signal.
Additionally, if the volume reduction is significant, it may cause the least significant bits (LSBs) of the audio samples to be truncated or rounded off during the scaling process. This can introduce quantization noise, which may become audible, especially in quieter passages of the audio.
So, while adjusting the volume digitally doesn't directly change the bit rate of the audio signal, it can affect the perceived audio quality due to changes in dynamic range and the potential introduction of quantization noise.
I'm not an engineer, but this makes sense to me, confirms the issues, and is well articulated I think - I love ChatGPT!