我试图得到一个c程序发送正弦波音调到我的树莓派使用ALSA的音频输出我生成的正弦波值的缓冲,但当我发送它们,它听起来不像一个正弦-但像低中频噪声?我已经将数组中的值转储到。csv中,并在excel中绘制以验证正弦波是否良好只是想知道在这个程序中是否有根本错误的东西,如果有人能指出一些地方,我会非常感激,谢谢
编辑:下面的最终工作代码!!
#include <alsa/asoundlib.h>
#include <alsa/pcm.h>
#include <math.h>
#define BUFFER_LEN 48000
static char *device = "default"; //soundcard
snd_output_t *output = NULL;
float buffer [BUFFER_LEN];
int main(void)
{
int err;
int j,k;
int f = 440; //frequency
int fs = 48000; //sampling frequency
snd_pcm_t *handle;
snd_pcm_sframes_t frames;
// ERROR HANDLING
if ((err = snd_pcm_open(&handle, device, SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
printf("Playback open error: %sn", snd_strerror(err));
exit(EXIT_FAILURE);
}
if ((err = snd_pcm_set_params(handle,
SND_PCM_FORMAT_FLOAT,
SND_PCM_ACCESS_RW_INTERLEAVED,
1,
48000,
1,
500000)) < 0) {
printf("Playback open error: %sn", snd_strerror(err));
exit(EXIT_FAILURE);
}
// SINE WAVE
printf("Sine tone at %dHz ",f);
for (k=0; k<BUFFER_LEN; k++){
buffer[k] = (sin(2*M_PI*f/fs*k)); //sine wave value generation
}
for (j=0; j<5; j++){
frames = snd_pcm_writei(handle, buffer, BUFFER_LEN); //sending values to sound driver
}
snd_pcm_close(handle);
return 0;
}
您已经配置了示例格式SND_PCM_FORMAT_U8
,但实际缓冲区包含32位浮点示例。
使用SND_PCM_FORMAT_FLOAT
,或者将缓冲区定义为unsigned char
的数组。
此外,您混淆了初始化buffer
的循环和播放数据的循环,以及许多字节/帧数,fs
是错误的;您需要使用如下内容:
for (i = 0; i < BUFFER_LEN; i++)
buffer [i] = sin(2*M_PI*f/48000*i); // sine wave value generation
for (i = 0; i < 10 * 48000 / BUFFER_LEN; i++) { // 10 seconds
frames = snd_pcm_writei(handle, buffer, BUFFER_LEN);
if (frames < 0)
frames = snd_pcm_recover(handle, frames, 0);
if (frames < 0) {
printf("snd_pcm_writei failed: %sn", snd_strerror(frames));
break;
}
if (frames > 0 && frames < BUFFER_LEN)
printf("Short write (expected %li, wrote %li)n", BUFFER_LEN, frames);
}