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RE: Bits and digital attenuation

Posted by Tony Lauck (A) on July 22, 2014 at 18:33:08

In Reply to: RE: Bits and digital attenuation posted by shane. on July 22, 2014 at 17:14:09:

Assuming the application works correctly and is set to output 32 bits, then when playing a 16 bit file at 100% volume it would output the high order 16 bits and fill all the remainder at zero. It would be a mistake to configure the ap to output at 32 bits with a 16 bit DAC. So I would assume that the DAC accepts 32 bit input. If the DAC works correctly then it will produce the same results on a 32 bit input with 16 low order zeros as it would have with a 16 bit input.

If the application applies digital volume control (or upsampling) the resulting processing will add additional low order bits depending on what was done. If the output was set to 32 bits then there would be no loss of resolution on volume control until 16 bits of digital volume control were applied, which would amount to a volume reduction of -96 dB. So in this case no resolution would be lost in sending data to the DAC.

Of course the DAC almost certainly doesn't have 32 bit resolution, but that's a different question. The details of what you hear will depend on the DAC. It could be that what you hear will be better with a lower digital signal into the DAC instead of sending a full volume digital signal into the DAC and then reducing it downstream by an analog volume control. This is the situation with my Mytek DAC. Here I use a built in digital volume control in the SABRE chip that works at 32 bits. There is no loss of digital resolution at the settings I typically use, e.g. -16 dB, starting with 24 bit sources. There is more gain out of the DAC and so any noise will be amplified. However, I can't hear any noise out the speakers, even if I put my ears right at them. So there is no real loss of signal to noise resolution going this way. Actually, the music sounds better, because the op-amps in my DAC have less distortion when they are working at a lower output level.

If you are using a 16 bit DAC then you should not use a digital volume control, because you need to use all the limited resolution how have. Given that there are DAC chips that provide higher resolution why would any one want to use an antiquated 16 bit DAC chip? If one subscribes to the NOS religion there are DAC chips that work at higher bit depths.

Tony Lauck

"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar

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