[alsa-devel] SoC Machine Code Suggestions

Liam Girdwood lg at opensource.wolfsonmicro.com
Wed Jun 27 18:48:08 CEST 2007

On Wed, 2007-06-27 at 10:47 -0500, Paul Kavan wrote:

> First. when the pcm interface starts/stops, I get a pop that comes from the
> codec analog output transitioning some. 

Does your codec have a digital mute ?

Fwiw, you may want read the application notes in the codec datasheet for
minimising any pops and clicks. 

It's also sometimes useful to minimise any output gains at startup and
then ramp them up to the desired volume before playback starts on some

> Now, there may be some hardware
> fixes to this, but what I would like to do it mute the amp until the last
> possible second before audio is played. I can accomplish this with a simple
> gpio call, but am not sure where best to turn the mute on and off. Any
> suggestions with that would be appreciated.

Turning the amp on and off will probably also cause a pop. It's just a
matter of finding what pops the least. You could add your GPIO amp code
to the machine driver say in startup/shutdown, but please bear in mind
the amp may take a little time to get up and running. 


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