Re: [linux-audio-dev] ATI-IXP overdrives PCM

From: Gene Heskett <gene.heskett@email-addr-hidden>
Date: Sun May 21 2006 - 15:24:18 EEST

James Courtier-Dutton wrote:
> c wrote:
>> On Sat May 20, 2006 at 09:27:56AM -0500, Gene Heskett wrote:
>>> often sounding as if the playback is of a file that over-drove the d/a in playback, or the a/d in the recording, eg clipped.
>> ...
>>> the ATI-IXP audio stuffs loaded
>> the ATIIXP in my MSI exhibits this same issue. essentially, if the 'PCM' level is set to 100%, things are horribly overdriven. the solution is to set the Master to 100%, and adjust volume with PCM, instead of vice versa. i guess whether this is a hardware bug or a driver bug depends on if PCM is the last point of software contact with the stream and master trims the levels after that, or if PCM just does some multiplication on the bits before passing them to the Master..
>
> If you are using alsamixer to set gain levels, that currently it is kind
> of hit and miss as to what 100% actually means.
> On some cards 100% is 0dB gain, on others it can be +12dB gain.
> So, setting your control to 100% might be causing a +12dB gain to the
> signal, that of course would over drive it and cause clipping.
>
> I will be implementing at some point, support for displaying dB gain
> values in alsamixer, so the problem you are having will disappear,
> because you will be able to then tell exactly what position to put the
> gain slider to get 0dB gain.
>
> James

That would be hardware dependent of course, but first, I need to make
the hardware work. How am I to know when grip is running and ripping a
cd that I can't hear the contents of till its been ripped, if the gain
control labeled 'cd' actually works? To me, its an extra eye candy only
control in kmix's window.
>
>

-- 
Cheers, Gene
Received on Mon May 22 12:15:12 2006

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