[off-topic] Applying gain to an audio sample
Marcel Bonnet
marcelbonnet at gmail.com
Fri Dec 20 22:02:49 UTC 2019
Em sex, 20 de dez de 2019 15:46, Hans Petter Selasky <hps at selasky.org>
escreveu:
> On 2019-12-20 19:43, Marcel Bonnet wrote:
> > - read an audio sample as integer (stereo 16 bit LE)
> > - convert to float
> > - apply a gain, like: sample *= 0.3f
> > - convert to integer again
>
> The attachment is missing.
>
Sorry, here it is.
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include "/usr/include/sys/soundcard.h"
#include <sys/ioctl.h>
#include <sys/time.h>
#include <sys/stat.h> //man 2 chmod
#include <signal.h>
#define DEBUG 1
#define log(msg) if (DEBUG) printf("[LOG] %s\n",msg)
#define err(msg) {printf("[ERR] %s\n",msg); exit(1); }
const char *device = "/dev/dsp3.1"; //Audio device
char *rawFile = "/tmp/raw-file.wav"; //Raw file to record and playback
int fragmentSize = 256;
int b_continue = 1;
void signalHandler(int sigNum){
log("Signal captured");
b_continue = 0;
}
void configDevice(int fdDsp){
int ossCapabilities = 0;
if(fdDsp == -1)
err("can't open device");
if( ioctl(fdDsp, SNDCTL_DSP_GETCAPS, &ossCapabilities) == -1)
err("unsupported: SNDCTL_DSP_GETCAPS");
/*
* http://www.opensound.com/pguide/audio2.html
*/
if(ossCapabilities & DSP_CAP_TRIGGER != DSP_CAP_TRIGGER){
err("Triggering of recording/playback is not possible with
this OSS device.");
}
if(ossCapabilities & DSP_CAP_REALTIME != DSP_CAP_REALTIME){
err("No DSP_CAP_REALTIME.");
}
if(ioctl(fdDsp, SNDCTL_DSP_SETDUPLEX, &ossCapabilities) == -1)
err("can't SNDCTL_DSP_SETDUPLEX");
if(ossCapabilities & DSP_CAP_DUPLEX != DSP_CAP_DUPLEX)
err("can't DSP_CAP_DUPLEX");
int format = AFMT_S16_LE; //set format
if(ioctl(fdDsp, SNDCTL_DSP_SETFMT, &format ) == -1){
err("Error setting format.");
}
int channels = 1; //mono=0 stereo=1
if(ioctl(fdDsp, SNDCTL_DSP_STEREO, &channels ) == -1){
err("Error setting channels." );
}
// FREQUENCY RATE
int speed = 44100;
if(ioctl(fdDsp, SNDCTL_DSP_SPEED, &speed ) == -1){
err("Error setting speed.");
}
// FRAGMENT SIZE
if(ioctl(fdDsp, SNDCTL_DSP_SETBLKSIZE, &fragmentSize) == -1){
//normalmente 2048 bits
err("Cannot SNDCTL_DSP_SETBLKSIZE.");
}
}
void record(){
int fdDsp = open(device, O_RDONLY);
configDevice(fdDsp);
//create file for writing
const int fdOutput = open(rawFile, O_WRONLY | O_CREAT, S_IWUSR | S_IRUSR);
if(fdOutput ==-1)
err("can't open file to write");
log("Recording...");
do{
// Triggers recording
int enableBits = PCM_ENABLE_INPUT;
if(ioctl(fdDsp, SNDCTL_DSP_SETTRIGGER, &enableBits) == -1)
err("Can't record: SNDCTL_DSP_SETTRIGGER");
int *buf[fragmentSize];
read(fdDsp, buf, fragmentSize);
write(fdOutput, buf, fragmentSize);
} while(b_continue == 1);
close(fdOutput);
close(fdDsp);
}
void playback(){
log("Opening file:");
log(rawFile);
log("On device:");
log(device);
int fdDsp = open(device, O_WRONLY);
configDevice(fdDsp);
const int fdInput = open(rawFile, O_RDONLY);
if(fdInput ==-1)
err("can't open file");
log("Playing...");
int eof = 0;
do{
// TRIGGERs PLAYBACK
int enableBits = PCM_ENABLE_OUTPUT;
if(ioctl(fdDsp, SNDCTL_DSP_SETTRIGGER, &enableBits) == -1){
err("Cannot SNDCTL_DSP_SETTRIGGER.");
}
int buf[fragmentSize];
eof = read(fdInput, buf, fragmentSize); //bytes read or -1 if EOF
// audio processing:
for(int i=0;i<fragmentSize;i++){
// learning how to get left and right channels from buffer
int l = (buf)[i] & 0xffff;
int r = ((buf)[i] >> 16) & 0xffff ;
// FIXME: it is causing distortion:
float fl = l;
float fr = r;
fl *= 1.0;
fr *= 0.3; //if different than 1, sounds distorted and noisy
l = fl;
r = fr;
// OK: unite Left and Right channels again
int lr = (l ) | (r << 16);
// OK: other options to mix these two channels:
int lleft = l; //Just the left channel
int rright = (r << 16); //Just the right channel
int lmono = (l << 16) | l; //Left ch. on both channels
int rmono = (r << 16) | r; //Right ch. on both channels
// the output:
(buf)[i] = lr;
}
write(fdDsp, buf, fragmentSize);
if(b_continue == 0) break;
} while(eof > 0);
close(fdInput);
close(fdDsp);
}
int main(int argc, char *argv[])
{
signal(SIGINT, signalHandler);
log("Ctrl^C to stop recording/playback");
record();
b_continue = 1; playback();
log("Stopped.");
return 0;
}
> Probably better to use the host endian version of AFMT
You mean AFMT_S16_NE ? The native endian?
> --HPS
>
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