Re: [Alsa-user] S/PDIF Volume

[Clemens L. <cla...@go...>]

Thor Kristoffersen wrote:
> I never understood the need for bit-exactness anyway.  With 24 bits of
> resolution it seems like a requirement based more on neurosis than
> reality.

Real-world DACs never have more than about 20 bits of actual resolution,
so there is sufficient headroom for doing calculations on the samples,
and even 16 bits is enough for human ears when the range is fully used.

However, there are situations where a volume control on the digital
output might lead to problems.  Imagine a user who wants to control the
volume on his computer, so he sets the receiver's volume to eleven, to
be sure that even very silent audio files can be played properly.  This
means that 'normal' over-compressed audio files must be played with a
volume setting of, say, -35 dB on the computer, so, if the receiver's
DAC has a SNR of about 100 dB, the resulting effective SNR is only
65 dB.  And then he complains because his digital system sounds so bad.

In the general case, attenuation should always be done after the
digital-to-analog conversion.  It would have been a good idea if the
S/PDIF protocol had allowed to transfer volume information to be applied
after the DAC.


Regards,
Clemens