[Alsa-user] Sine wave

[Mike M. <ma...@st...>]

Hello!

I=B4m playing around with ALSA and I want=20
to create a simple sine wave.
The program compiles fine and a tone is played
but the tone is around a# and not a.
There are some things I dont=B4t understand:

How do I choose the right buffer size, period size and periods and
what is the difference between interleaved and non-interleaved?

I have read several tutorials but they confuse me much more, because
it seems that there are more ways to do this.

I=B4m not a C geek, so help is appreciated!!



#include <stdio.h>
#include <math.h>
#include <alsa/asoundlib.h>

int main(int argc,char *argv[]){
=09

	char *device =3D "hw:0,0";=20
=09
	int samples,err,i,dir =3D 0;
	unsigned int samplerate =3D 44100;
	unsigned int channels =3D 1;
	double frequency =3D 440.0;=20
	double buffer[4096];
=09
	snd_pcm_format_t format =3D SND_PCM_FORMAT_S16_LE;=20
	snd_pcm_access_t access =3D SND_PCM_ACCESS_RW_INTERLEAVED;=20
        snd_pcm_stream_t stream =3D SND_PCM_STREAM_PLAYBACK;
=09
	snd_pcm_t *handle;
        snd_pcm_hw_params_t *hwparameter;
=09
	printf("ALSA Version: %s\n",SND_LIB_VERSION_STR);
=09
	snd_pcm_hw_params_alloca(&hwparameter);

	if((err =3D snd_pcm_open(&handle, device, stream,0))<0){
		printf("Could not open soundcard %s: %s",device,snd_strerror(err));=20
	exit(0);
	}
        if((err =3D snd_pcm_hw_params_any(handle,hwparameter))<0){
		printf("Error: %s\n",snd_strerror(err));
	}
	if((err =3D snd_pcm_hw_params_set_access(handle,hwparameter,access))<0){
		printf("Could not set RW mode %s\n",snd_strerror(err));
		exit(0);
	}
	if((err =3D snd_pcm_hw_params_set_format(handle,hwparameter,format))<0){
		printf("Could not set bit format: %s\n",snd_strerror(err));
		exit(0);
	}
	if((err =3D snd_pcm_hw_params_set_channels(handle,hwparameter,channels))<0=
){
		printf("Could not set channels: %s\n",snd_strerror(err));=20
	}
        if((err =3D snd_pcm_hw_params_set_rate_near(handle,hwparameter,&sam=
plerate,&dir))<0){
		printf("Could not set samplerate: %s\n",snd_strerror(err));
	}
	if((err =3D snd_pcm_hw_params(handle,hwparameter))<0){
	        printf("Could not set HW params: %s\n",snd_strerror(err));
	}
	/*create sine wave*/
	samples =3D samplerate/frequency;
=09
	for(i=3D0;i<=3Dsamples;i++){
	buffer[i] =3D sin((2 * M_PI * i)/samples);
	}=09
=09
	while(1){
		if((err =3D snd_pcm_writei(handle,&buffer,samples))<0){
		printf("Could not play stream: %s\n",strerror(err));
		}
	}
	snd_pcm_close(handle);=20
	return 0;

}

Thanks a lot,

Mike