我很难在Linux期刊中找到ALSA示例
我将代码复制到.c文件中，并将它们gcc -Wall Record_Listing4.c -lasound -o record编译为可执行文件：列表3为play，列表4为record
我正在使用Nanopo NEO和UGO声卡
我确保将默认的音频设备指向提到的USB声卡。
我可以用这个examles录制声音，甚至可以听，但有一个问题：如果我按原样播放./record | ./play，我会得到超级大的高音噪音作为背景。
我发现我的耳机需要2声道立体声，而我的麦克风只能产生1声道单声道。所以我试着把这个单声道和它自己交织起来，创造立体声。
这给我带来了一些成功，因为我设法摆脱了高音噪音，但现在我的声音却产生了一些静态噪音。
这是我第一次尝试直接使用声音创建应用程序，所以我试图理解为什么我会收到噪音。arecord工作得很好，记录没有问题，所以它不是硬件。
修改后的以下代码
Playback_Listing3
/*
This example reads standard from input and writes
to the default PCM device for 5 seconds of data.
*/
/* Use the newer ALSA API */
#define ALSA_PCM_NEW_HW_PARAMS_API
#include <alsa/asoundlib.h>
int main() {
long loops;
int rc;
int size;
snd_pcm_t *handle;
snd_pcm_hw_params_t *params;
unsigned int val;
int dir;
snd_pcm_uframes_t frames;
char *buffer;
/* Open PCM device for playback. */
rc = snd_pcm_open(&handle, "default",
SND_PCM_STREAM_PLAYBACK, 0);
if (rc < 0) {
fprintf(stderr,
"unable to open pcm device: %sn",
snd_strerror(rc));
exit(1);
}
/* Allocate a hardware parameters object. */
snd_pcm_hw_params_alloca(¶ms);
/* Fill it in with default values. */
snd_pcm_hw_params_any(handle, params);
/* Set the desired hardware parameters. */
/* Interleaved mode */
snd_pcm_hw_params_set_access(handle, params,
SND_PCM_ACCESS_RW_INTERLEAVED);
/* Signed 16-bit little-endian format */
snd_pcm_hw_params_set_format(handle, params,
SND_PCM_FORMAT_S16_LE);
/* Two channels (stereo) */
snd_pcm_hw_params_set_channels(handle, params, 2);
/* 44100 bits/second sampling rate (CD quality) */
val = 44100;
snd_pcm_hw_params_set_rate_near(handle, params,
&val, &dir);
/* Set period size to 32 frames. */
frames = 32;
snd_pcm_hw_params_set_period_size_near(handle,
params, &frames, &dir);
/* Write the parameters to the driver */
rc = snd_pcm_hw_params(handle, params);
if (rc < 0) {
fprintf(stderr,
"unable to set hw parameters: %sn",
snd_strerror(rc));
exit(1);
}
/* Use a buffer large enough to hold one period */
snd_pcm_hw_params_get_period_size(params, &frames,
&dir);
size = frames * 4; /* 2 bytes/sample, 2 channels */
buffer = (char *) malloc(size);
/* We want to loop for 5 seconds */
snd_pcm_hw_params_get_period_time(params,
&val, &dir);
/* 5 seconds in microseconds divided by
* period time */
loops = 5000000 / val;
while (loops > 0) {
loops--;
rc = read(0, buffer, size);
if (rc == 0) {
fprintf(stderr, "end of file on inputn");
break;
} else if (rc != size) {
fprintf(stderr,
"short read: read %d bytesn", rc);
}
rc = snd_pcm_writei(handle, buffer, frames);
if (rc == -EPIPE) {
/* EPIPE means underrun */
fprintf(stderr, "underrun occurredn");
snd_pcm_prepare(handle);
} else if (rc < 0) {
fprintf(stderr,
"error from writei: %sn",
snd_strerror(rc));
} else if (rc != (int)frames) {
fprintf(stderr,
"short write, write %d framesn", rc);
}
}
snd_pcm_drain(handle);
snd_pcm_close(handle);
free(buffer);
return 0;
}
Record_Listing4
/*
This example reads from the default PCM device
and writes to standard output for 5 seconds of data.
*/
/* Use the newer ALSA API */
#define ALSA_PCM_NEW_HW_PARAMS_API
#include <alsa/asoundlib.h>
void interleave(const char * in_L, // mono input buffer (left channel)
const char * in_R, // mono input buffer (right channel)
char * out, // stereo output buffer
const size_t num_samples) // number of samples
{
for (size_t i = 0; i < num_samples; ++i)
{
out[i * 4] = in_L[i];
out[i * 4 + 1] = in_L[i+1];
out[i * 4 + 2] = 0;
out[i * 4 + 3] = 0;
}
}
int main() {
long loops;
int rc;
int size;
snd_pcm_t *handle;
snd_pcm_hw_params_t *params;
unsigned int val;
int dir;
snd_pcm_uframes_t frames;
char *buffer;
char *stereo;
/* Open PCM device for recording (capture). */
rc = snd_pcm_open(&handle, "default",
SND_PCM_STREAM_CAPTURE, 0);
if (rc < 0) {
fprintf(stderr,
"unable to open pcm device: %sn",
snd_strerror(rc));
exit(1);
}
/* Allocate a hardware parameters object. */
snd_pcm_hw_params_alloca(¶ms);
/* Fill it in with default values. */
snd_pcm_hw_params_any(handle, params);
/* Set the desired hardware parameters. */
/* Interleaved mode */
snd_pcm_hw_params_set_access(handle, params,
SND_PCM_ACCESS_RW_INTERLEAVED);
/* Signed 16-bit little-endian format */
snd_pcm_hw_params_set_format(handle, params,
SND_PCM_FORMAT_S16_LE);
/* Two channels (stereo) */
snd_pcm_hw_params_set_channels(handle, params, 1);
/* 44100 bits/second sampling rate (CD quality) */
val = 44100;
snd_pcm_hw_params_set_rate_near(handle, params, &val, &dir);
/* Set period size to 32 frames. */
frames = 32;
snd_pcm_hw_params_set_period_size_near(handle, params, &frames, &dir);
/* Write the parameters to the driver */
rc = snd_pcm_hw_params(handle, params);
if (rc < 0) {
fprintf(stderr,
"unable to set hw parameters: %sn",
snd_strerror(rc));
exit(1);
}
/* Use a buffer large enough to hold one period */
snd_pcm_hw_params_get_period_size(params,
&frames, &dir);
size = frames * 2; /* 2 bytes/sample, 2 channels */
buffer = (char *) malloc(size);
stereo = (char *) malloc(size*2);
/* We want to loop for 5 seconds */
snd_pcm_hw_params_get_period_time(params,
&val, &dir);
loops = 5000000 / val;
while (loops > 0) {
loops--;
rc = snd_pcm_readi(handle, buffer, frames);
if (rc == -EPIPE) {
/* EPIPE means overrun */
fprintf(stderr, "overrun occurredn");
snd_pcm_prepare(handle);
} else if (rc < 0) {
fprintf(stderr,
"error from read: %sn",
snd_strerror(rc));
} else if (rc != (int)frames) {
fprintf(stderr, "short read, read %d framesn", rc);
}
interleave(buffer, buffer, stereo, frames);
rc = write(1, stereo, size*2);
if (rc != size*2)
fprintf(stderr,
"short write: wrote %d bytesn", rc);
}
snd_pcm_drain(handle);
snd_pcm_close(handle);
free(buffer);
return 0;
}
更新
我设法解决了这个问题。背后的原因是记录格式和回报格式不一致。我需要正确地将麦克风中的单声道交错，以创建正确的立体声，而不会产生噪音或静电。我在下面为任何挣扎的人发布代码。
记录
/*
This example reads from the default PCM device
and writes to standard output for 5 seconds of data.
*/
/* Use the newer ALSA API */
#define ALSA_PCM_NEW_HW_PARAMS_API
#include <alsa/asoundlib.h>
void interleave(const uint16_t * in_L, // mono input buffer (left channel)
const uint16_t * in_R, // mono input buffer (right channel)
uint16_t * out, // stereo output buffer
const size_t num_samples) // number of samples
{
for (size_t i = 0; i < num_samples; ++i)
{
out[i*2] = in_L[i];
out[i*2+1] = in_R[i];
}
}
int main() {
long loops;
int rc;
int size;
snd_pcm_t *handle;
snd_pcm_hw_params_t *params;
unsigned int val;
int dir;
snd_pcm_uframes_t frames;
char *buffer;
char *stereo;
snd_pcm_format_t format = SND_PCM_FORMAT_S16_LE;
int channels = 2;
/* Open PCM device for recording (capture). */
rc = snd_pcm_open(&handle, "default",
SND_PCM_STREAM_CAPTURE, 0);
if (rc < 0) {
fprintf(stderr,
"unable to open pcm device: %sn",
snd_strerror(rc));
exit(1);
}
/* Allocate a hardware parameters object. */
snd_pcm_hw_params_alloca(¶ms);
/* Fill it in with default values. */
snd_pcm_hw_params_any(handle, params);
/* Set the desired hardware parameters. */
/* Interleaved mode */
snd_pcm_hw_params_set_access(handle, params,
SND_PCM_ACCESS_RW_INTERLEAVED);
/* Signed 16-bit little-endian format */
snd_pcm_hw_params_set_format(handle, params, format);
/* Two channels (stereo) */
snd_pcm_hw_params_set_channels(handle, params, channels);
/* 44100 bits/second sampling rate (CD quality) */
val = 44100;
snd_pcm_hw_params_set_rate_near(handle, params, &val, &dir);
/* Set period size to 32 frames. */
frames = 128;
snd_pcm_hw_params_set_period_size_near(handle, params, &frames, &dir);
/* Write the parameters to the driver */
rc = snd_pcm_hw_params(handle, params);
if (rc < 0) {
fprintf(stderr,
"unable to set hw parameters: %sn",
snd_strerror(rc));
exit(1);
}
/* Use a buffer large enough to hold one period */
snd_pcm_hw_params_get_period_size(params, &frames, &dir);
int width = (snd_pcm_format_width(format)/8);
fprintf(stderr,"Format width: %dn", width);
size = frames * width; /* 2 bytes/sample, 2 channels */
buffer = (char *) malloc(size);
stereo = (char *) malloc(size*2);
for(int i = 0; i < 2*size; i++){
stereo[i] = 0x00;
}
/* We want to loop for 5 seconds */
snd_pcm_hw_params_get_period_time(params, &val, &dir);
loops = 5000000 / val;
while (loops > 0) {
loops--;
rc = snd_pcm_readi(handle, buffer, frames);
if (rc == -EPIPE) {
/* EPIPE means overrun */
fprintf(stderr, "overrun occurredn");
snd_pcm_prepare(handle);
} else if (rc < 0) {
fprintf(stderr,
"error from read: %sn",
snd_strerror(rc));
} else if (rc != (int)frames) {
fprintf(stderr, "short read, read %d framesn", rc);
}
if(channels > 1){
interleave((uint16_t*)buffer,(uint16_t*)buffer,(uint16_t*)stereo,frames);
write(1, stereo, 2*size);
}
else{
write(1, buffer, size);
}
}
snd_pcm_drain(handle);
snd_pcm_close(handle);
free(buffer);
return 0;
}
回放
/*
This example reads standard from input and writes
to the default PCM device for 5 seconds of data.
*/
/* Use the newer ALSA API */
#define ALSA_PCM_NEW_HW_PARAMS_API
#include <alsa/asoundlib.h>
int main() {
long loops;
int rc;
int size;
snd_pcm_t *handle;
snd_pcm_hw_params_t *params;
unsigned int rate = 44100;
int dir;
snd_pcm_uframes_t frames;
char *buffer;
char* stereo;
snd_pcm_format_t format = SND_PCM_FORMAT_S16_LE;
int channels = 2;
/* Open PCM device for playback. */
rc = snd_pcm_open(&handle, "default",
SND_PCM_STREAM_PLAYBACK, 0);
if (rc < 0) {
fprintf(stderr,
"unable to open pcm device: %sn",
snd_strerror(rc));
exit(1);
}
/* Allocate a hardware parameters object. */
snd_pcm_hw_params_alloca(¶ms);
/* Fill it in with default values. */
snd_pcm_hw_params_any(handle, params);
/* Set the desired hardware parameters. */
/* Interleaved mode */
snd_pcm_hw_params_set_access(handle, params,
SND_PCM_ACCESS_RW_INTERLEAVED);
/* Signed 16-bit little-endian format */
snd_pcm_hw_params_set_format(handle, params, format);
/* Two channels (stereo) */
snd_pcm_hw_params_set_channels(handle, params, channels);
/* 44100 bits/second sampling rate (CD quality) */;
rc = snd_pcm_hw_params_set_rate_near(handle, params, &rate, &dir);
if(rc < 0){
unsigned int r;
snd_pcm_hw_params_get_rate(params, &r, &dir);
fprintf(stderr, "cannot set sample rate, using: %dn", r);
}
/* Set period size to 32 frames. */
frames = 128;
snd_pcm_hw_params_set_period_size_near(handle,
params, &frames, &dir);
/* Write the parameters to the driver */
rc = snd_pcm_hw_params(handle, params);
if (rc < 0) {
fprintf(stderr,
"unable to set hw parameters: %sn",
snd_strerror(rc));
exit(1);
}
/* Use a buffer large enough to hold one period */
snd_pcm_hw_params_get_period_size(params, &frames,
&dir);
size = frames * (snd_pcm_format_width(format)/8) * channels; /* 2 bytes/sample, 2 channels */
buffer = (char *) malloc(size);
stereo = malloc(2*size);
/* We want to loop for 5 seconds */
snd_pcm_hw_params_get_period_time(params, &rate, &dir);
/* 5 seconds in microseconds divided by
* period time */
loops = 5000000 / rate;
while (loops > 0) {
loops--;
rc = read(0, buffer, size);
if (rc == 0) {
fprintf(stderr, "end of file on inputn");
break;
} else if (rc != size) {
fprintf(stderr,
"short read: read %d bytesn", rc);
}
rc = snd_pcm_writei(handle, buffer, frames);
if (rc == -EPIPE) {
/* EPIPE means underrun */
fprintf(stderr, "underrun occurredn");
snd_pcm_prepare(handle);
} else if (rc < 0) {
fprintf(stderr,
"error from writei: %sn",
snd_strerror(rc));
} else if (rc != (int)frames) {
fprintf(stderr,
"short write, write %d framesn", rc);
}
}
snd_pcm_drain(handle);
snd_pcm_close(handle);
free(buffer);
return 0;
}