[alsa-devel] alsa-lib: Rate conversion broken for non-S16?

[Mark Hills]

Hi, does anybody have any thoughts on my email below? The rate conversion 
code looks stable and untouched for a while.

Thanks

On Sun, 1 Aug 2010, Mark Hills wrote:

> I have a device (snd-usb-caiaq) whose native sample format is S24_3BE. 
> When sample rate conversion is used, the audio becomes near silent, 
> distorted, and only in the left channel.
> 
> It is reproducable with aplay (see example below). Recording is not 
> affected. Playback is correct if only format conversion is used.
> 
> It looks something is causing the incorrect put function to be used by the 
> rate conversion.
> 
> I traced it to linear_expand() and others, alsa-lib-src/pcm_rate_linear.c.
> 
> Forcing the function to put S16 format into the destination buffer allows, 
> suprisingly, the sound to be heard correctly and at full volume from both 
> aplay and xwax:
> 
>   if (rate->put_idx == 10)
>       rate->put_idx = 6
> 
> I suspected that linear_init() is looking in the wrong place to choose the 
> attributes for the rate conversion. After some time spent I cannot see it.
> 
> But is there any reason that the output buffer for the rate conversion 
> would not be in S24_3BE? And for the rate conversion to be misinformed?
> 
> $ uname -s -r -v -p -i -m
> Linux 2.6.34.1-mh #83 SMP PREEMPT Wed Jul 21 23:25:33 BST 2010 i686 pentium4 i386
> 
> $ alsacap
> Card 0, ID `Audio8DJ', name `Audio 8 DJ'
>   Device 0, ID `Audio 8 DJ', name `Audio 8 DJ', 4 subdevices (4 available)
>     2 channels, sampling rate 44100..96000 Hz
>     Sample formats: S24_3BE
>       Subdevice 0, name `subdevice #0'
>       Subdevice 1, name `subdevice #1'
>       Subdevice 2, name `subdevice #2'
>       Subdevice 3, name `subdevice #3'
> 
> $ aplay -v -D plughw:Audio8DJ,0,0 halcyon-24000.wav 
> Playing WAVE 'halcyon-24000.wav' : Signed 16 bit Little Endian, Rate 24000 Hz, Stereo
> Plug PCM: Rate conversion PCM (48000, sformat=S24_3BE)
> Converter: linear-interpolation
> Protocol version: 10002
> Its setup is:
>   stream       : PLAYBACK
>   access       : RW_INTERLEAVED
>   format       : S16_LE
>   subformat    : STD
>   channels     : 2
>   rate         : 24000
>   exact rate   : 24000 (24000/1)
>   msbits       : 16
>   buffer_size  : 10922
>   period_size  : 2730
>   period_time  : 113770
>   tstamp_mode  : NONE
>   period_step  : 1
>   avail_min    : 2730
>   period_event : 0
>   start_threshold  : 10922
>   stop_threshold   : 10922
>   silence_threshold: 0
>   silence_size : 0
>   boundary     : 715784192
> Slave: Hardware PCM card 0 'Audio 8 DJ' device 0 subdevice 0
> Its setup is:
>   stream       : PLAYBACK
>   access       : MMAP_INTERLEAVED
>   format       : S24_3BE
>   subformat    : STD
>   channels     : 2
>   rate         : 48000
>   exact rate   : 48000 (48000/1)
>   msbits       : 24
>   buffer_size  : 21845
>   period_size  : 5461
>   period_time  : 113770
>   tstamp_mode  : NONE
>   period_step  : 1
>   avail_min    : 5461
>   period_event : 0
>   start_threshold  : 21844
>   stop_threshold   : 21845
>   silence_threshold: 0
>   silence_size : 0
>   boundary     : 1431633920
>   appl_ptr     : 0
>   hw_ptr       : 0
> 
> 

-- 
Mark