[linux-audio-dev] Re: Mixer controls

Juhana Sadeharju kouhia at nic.funet.fi
Thu Nov 10 14:24:25 UTC 2005

>From: James Courtier-Dutton <James at superbug.co.uk>
>It was just an example. The actual range depends on the sound card 
>hardware, but the typical limit is something like -60 dB or -80 dB.

Do you process each channel with audio software prior mixing?
If yes, then I would suggest to fix the hardware levels to
the optimum level, and use gains only in software.

As FA wrote, soundcards most likely do not have click-free mutes
and smooth gains. When the hardware is fixed, you may do faded
mutes in software with good quality.

Fixing the hardware input and output levels makes sense to me.
The input devices all have fixed SNR -- it does not help to
crank up the soundcard input level as it brings the noise up.
The output would be fixed for the same reasons.

Also, fixing the output prevents you accidentally damage the
speakers and your ears. When you crank up the gain in software,
you may have a software limiter prior the monitor outputs.
Once I watched when a friend mastered CDs. The fades were
auditioned by cranking up the level on the mixer desk. A couple of
times happened that the level was not set back to normal position
when needed. :-|  By fixing the hardware (including external mixer
desk) in the audio path, you may have full control with the software.

Soundcards are not optimal for listening fades. Only software gain
allows one to audition the fades. With hardware gain the sound can
be muddy, but most likely your card cannot make +64 dB gains
needed in listening the fades.

Cards equipped with an user-programmable dsp chip allows one to move
the code from the software to the firmware. I'm in understanding
that in SB Live all hardware gains are actually software gains.
I.e., they have fixed the hardware.

  for developers of open source graphics software

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