[alsa-devel] Audio crackles with 4.1-rc1

[Mihai Donțu]

On Wed, 10 Jun 2015 20:23:01 +0200 Takashi Iwai wrote:
> From: Takashi Iwai <tiwai at suse.de>
> Subject: [PATCH] ALSA: hda - Reduce click noise at power up
> 
> Some machines suffer from click noises at power up with the recent
> kernels, and this seems triggered at the power transition and the
> immediate verb executions.  As a workaround, put a short delay (10ms)
> right after the D0 transition.
> 
> There are a few places that have the same kind of delays, especially
> in the resume path.  I guess they can be removed (or reduced) after
> this patch.  But, since the delay is relatively small, let's do it
> later as a cleanup.
> 
> Reported-by: Mihai Donțu <mihai.dontu at gmail.com>
> Signed-off-by: Takashi Iwai <tiwai at suse.de>
> ---
>  sound/pci/hda/hda_codec.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/sound/pci/hda/hda_codec.c b/sound/pci/hda/hda_codec.c
> index b7782212dd64..38f5509ee52f 100644
> --- a/sound/pci/hda/hda_codec.c
> +++ b/sound/pci/hda/hda_codec.c
> @@ -3077,6 +3077,9 @@ static unsigned int hda_set_power_state(struct hda_codec *codec,
>  			break;
>  	}
>  
> +	if (power_state == AC_PWRST_D0)
> +		msleep(10);
> +
>  	return state;
>  }
>  

I take back my previous observations. I was at work and did not have
access to headphones (one of those days). Now I'm at home, it's 1 AM,
very quiet, and I notice the following:

 * on speakers: the click reproduces but with _very_ low amplitude;
   msleep(100) is unnoticeable, but msleep(10) is, barely;
 * on headphones: the moment I plug them I hear a loud static sound
   (like an old, untuned AM radio). If I play something, the static
   disappears. If I pause, the static returns after ~15s.

-- 
Mihai Donțu