Re: Rate Conversion

[Kris Modrak <u9514439@anu.edu.au>]

Paul Davis wrote:
> 
> >I am a little confused about your advice. I am not sure how to access
> >the 'plughw' device from my application.
> 
>      snd_pcm_open (&handle, "plughw:N,M", ...)
> 
> where N and M are the card number and subdevice number. Preferably,
> this is a string supplied by the user, not hard coded into the application.
> 
> >I am not sure of how I should be setting up my PCM devices. How do I
> >tell them to convert, say, 8kHz audio data to 44.1kHz audio data so my
> >hardware can play it at the correct speed?
> 
> just as in the few token API examples. using
> snd_pcm_hw_params_*(). there is no difference setting the parameters
> no matter what "type" of PCM device you are using.

Apart from rates or 44.1 or 48kHz I was unable to find a rate/period
size combination that I was able to use with plughw:0,0.

snd_pcm_hw_params_set_period_size () failed for every period size I
tried (64, 128, 256, 512, 1024, 2048 and 4096) when I had the rate set
to 8, 16 or 32 kHz.

I managed to set the following combinations of hardware parameters:
-22050Hz with period sizes of 2048, 1024, 512, 256, 128 and 64
-11025Hz with period sizes of 1024, 512, 256, 128 and 64

but when I ran my application I encountered the following error

ALSA lib pcm_hw.c:380:(snd_pcm_hw_start) SNDRV_PCM_IOCTL_START failed:
Broken pipe

Does anyone have any further suggestions of things that I could try or
why this rate conversion isn't working for me? I am using ALSA
0.9.0beta12 with a Hammerfall Light (RME Digi9636) soundcard.

Kris Modrak


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