[alsa-devel] Audio quality issue - regular clicks are observed

[Pharaoh .]

On 8/23/07, Pharaoh . <pharaoh137 at gmail.com> wrote:
>
>
>
> On 8/23/07, Liam Girdwood <lg at opensource.wolfsonmicro.com > wrote:
> >
> > On Wed, 2007-08-22 at 22:13 +0530, Pharaoh . wrote:
> > > Hi
> > > While testing the audio driver using aplay in blocking mode, a
> > periodic
> > > murmur is observed, this increases with
> > > the audio volume and occurs even when there are no issues like xrun
> > etc.
> > > Aplay was used in normal read/write mode
> > > i.e. no mmap. The song can be heard properly i.e. with no noticable
> > gaps aur
> > > hisses but the clicks are audible.
> >
> > Clock domain mismatch issues cause periodic ticks that increase in
> > frequency with increasing sample rate. It's possible your clocking the
> > codec and controller in two different clock domains. i.e. I2S controller
> > (bitclk and frame) clocked from CPU and codec clocked from separate
> > crystal.
> >
> > It's best to make sure that only one clock is clocking both the codec
> > and digital audio interface.
> >
> > Liam
> >
> >
> I tried playing /dev/zero at the same sampling rate as a wav file, but
> /dev/zero played without any clicks i.e absolutely no sound heard, but
> while playing a wav file using same parameters clicks occur. I am thinking
> it is not about clocks mis-match, since I have checked it several times. I
> was thinking whether junk data is being processed at end of buffer size, but
> since /dev/zero plays well, I am ruling out that possibility also.
>
> What else could explain the latencies at buffer ending as shown in the log
> in previous mail.
>
> -Pharaoh.
>
>
>
>
>
>
Further debug reveals that the pointer callback is called multiple times at
the beginning of buffer . Could it be cause of latency? I am playing the
same .wav file with using aplay with 16K buffer size and 4K period size .

Here is the log, audio_get_dma_pos is my pointer function. In period 0 it is
called 4 times, while in period 1,2 and 3 it is called only once. Does it
mean that first time pointer is called it is not getting  correct value and
it keeps retrying till it gets some sensible value?

[ 1013.037107] current period = 0  current offset = c000
[ 1013.044950] audio_get_dma_pos
[ 1013.051770] audio_get_dma_pos
[ 1013.056944] audio_get_dma_pos
[ 1013.063780] audio_get_dma_pos
[ 1013.135178] audio_get_dma_pos
[ 1013.138445] current period = 1  current offset = 0
[ 1013.236261] audio_get_dma_pos
[ 1013.239453] current period = 2  current offset = 4000
[ 1013.337485] audio_get_dma_pos
[ 1013.340640] current period = 3  current offset = 8000
[ 1013.438684] audio_get_dma_pos
[ 1013.441886] current period = 0  current offset = c000
[ 1013.449263] audio_get_dma_pos
[ 1013.454452] audio_get_dma_pos
[ 1013.461301] audio_get_dma_pos
[ 1013.466879] audio_get_dma_pos
[ 1013.539984] audio_get_dma_pos
[ 1013.543208] current period = 1  current offset = 0
[ 1013.641070] audio_get_dma_pos
[ 1013.644283] current period = 2  current offset = 4000
[ 1013.742383] audio_get_dma_pos
[ 1013.745553] current period = 3  current offset = 8000
[ 1013.843631] audio_get_dma_pos
[ 1013.846833] current period = 0  current offset = c000
[ 1013.854221] audio_get_dma_pos
[ 1013.861027] audio_get_dma_pos
[ 1013.866227] audio_get_dma_pos
[ 1013.873090] audio_get_dma_pos
[ 1013.944925] audio_get_dma_pos
[ 1013.948187] current period = 1  current offset = 0
[ 1014.045988] audio_get_dma_pos
[ 1014.049177] current period = 2  current offset = 4000
[ 1014.147209] audio_get_dma_pos
[ 1014.150370] current period = 3  current offset = 8000


-pharaoh.