[alsa-devel] Set eapd to follow stream on or off

[Takashi Iwai]

At Tue, 20 May 2014 17:20:44 +0800,
Kailang wrote:
> 
> 
> > At Tue, 20 May 2014 16:52:43 +0800,
> > Kailang wrote:
> >>
> >>
> >> > At Tue, 20 May 2014 15:15:49 +0800,
> >> > Kailang wrote:
> >> >>
> >> >> Hi Takashi,
> >> >>
> >> >> HP machine had pop noise via speaker.
> >> >> If EAPD on or off, speaker will have pop noise.
> >> >> So, they want to set eapd to follow with stream on or off.
> >> >
> >> > I can apply this as is, but still I wonder whether this results in
> >> > other problems.  Doing EAPD on/off there means that it happens far
> >> > more often.  For example, what happens if you do like below?
> >> >
> >> >     while true; do
> >> >       echo -n > /dev/snd/pcmC0D0p
> >> >     done
> >> >
> >> > And, what if the device is resumed from power-saving by an audio
> >> > playback?  Immediately after the power up, it'll start the streaming,
> >> > so it'll turn on EAPD.
> >> >
> >> > That said, isn't it just a need for some delay before EAPD on/off?
> >>
> >> No, eapd on or off will cause pop noise.
> >
> > Does it do always?
> No, pop noise just one pop sound. It can not remove by software.
> But this machine need to do this always.

So, doing EAPD on/off often is rather worse.  It's what your patch
does.

Once again: did you try the script above?  If the pop noise always
happens, the operation like above is the worst scenario.

Then, let's think again how to *reduce* it.  We need one EAPD on at
least after each power up.  But it's needed only when you actually
plays a stream.  That is, we need only enable EAPD at playback stream
open, but leave EAPD as is at close.


Takashi

> >> Our customer just want to do eapd on when stream is open.
> >> The pop noise will not clear. Because music gain was biger than pop 
> >> noise.
> >
> > Opening a stream doesn't mean that it follows the loud sound
> > immediately.  The script above wouldn't produce any sound but just
> > does open/close the stream.  Did you try that?
> >
> >
> > Takashi
> >
> > ------Please consider the environment before printing this e-mail. 
>