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Pop and offsets at start of audio playback/record on imx28evk on 3.14 kernel

Question asked by Craig McQueen on Nov 10, 2014
Latest reply on Nov 12, 2014 by Craig McQueen

I'm testing the 3.14.19 kernel on imx28evk, with a Yocto build that uses the linux-fslc kernel provider.

 

Playback

 

When doing SGTL5000 audio playback on the imx28evk on 3.14 kernel, I notice that the audio "fades in" over the first (approximately) 500 ms of playback. This is very noticeable and not ideal in certain applications (e.g. audio notifications that are of short duration).

 

However, if audio playback starts while audio recording is already in-progress, then there is no fade-in; instead there is a loud pop. I assume the fade-in is there to mask the pop. The pop is very unpleasant through headphones.

 

I didn't think either the pop or the fade-in occurred on the 2.6.35 kernel. How feasible is it to improve the driver to avoid or reduce the pop, and remove the necessity for a fade-in? Or, make the fade-in faster so it doesn't so noticeably change the audio output?

 

Record

 

When recording, I notice there is a low-frequency ramping offset at the start of a recording (after the 400-500 ms of previous audio) of approx 600-700 ms duration. This also reduces the audio quality at the start of the recording. It could potentially cause clipping of a loud signal, or otherwise reduce the quality of captured audio depending on the application usage. It could cause a pop on playback (local playback or e.g. VoIP transmission to a remote device). It could reduce the audio quality through an audio CODEC.

 

How feasible is it to improve the driver to avoid a ramping offset at the start of recording?

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