Multiple streams
All popular operating systems (Windows, OSX, Linux, Android) are designed to play multiple audio streams.
You watch a video but you want to hear a notification when a email arrives.
The only way to obtain this is to mix the audio and the system sound.
You can only mix if all streams run at the same sample rate.
The audiostreams are converted to float (to keep the quantization error down), mixed, dithered and converted back to integer.
Dither (adding random noise) is applied to decorrelated the audio and the quantization error.
In case of 16 bit, it is a must.
Today as most DAC’s do have a 24 bit input, you might wonder is dither at -144 dBFS is of any significance.
An obvious consequence of multiple audio streams is that you do have to choose a fixed sample rate and a bit depth in the audio settings of the OS.
Bit depth.
Simply set it to the max as supported by your audio device.
If you play a 16 bit file and the setting is 24 bit, 8 zero bits are added with zero impact on sound quality.
Choosing the highest bit depth regardless of your source can be beneficial when applying DSP.
Something as simple as digital volume control will result in loss of resolution if the bit depth is 16 bits.
Turn the volume down with 48 dB
1111111111111111
0000000011111111 only 8 bits left using a 16 bit word length.
Do the same using a 24 bit word
111111111111111100000000
000000001111111111111111 still 16 bits left using a 24 bit word length.
Sample rate.
This is a different matter.
Certainly in the past, re-sampling often means disaster. It resulted in measurable and audible distortion.
Today it is done pretty transparent.
Your best bet is to set the sample rate to what is common.
Most of our audio is 44.1 kHz.
768kHz!
This is probably the max the USB UAC2 audio receiver accepts.
As USB does device enumeration, you probably see all supported sample rates in the audio panel.
Don’t be surprised if the DAC (the chip inside the box) runs at a completely different rate. In fact most DAC’s do apply ASRC (Asynchronous Sample Rate Conversion) to get rid of the input jitter hence do have a free running clock.
The consequence of 768 is all the audio is resample twice, up to 768 by the media player and then down to xxx by the DAC.
IMHO
- set bit depth to the max supported by the audio device
- set the fixed sample rate to what is common (44.1 kHz)
- if possible use automatic sample rate switching