PulseAudio API - No Microphone Signal - c

Question

I'm trying to capture a microphone signal in "real-time" using PulseAudio. The program is written in C and uses the PulseAudio Simple API for that. Unfortunately my requested audio buffer does not contain any signal. Either there's a problem in my code or the device source just does not get recognized. I ran some tests outside my program with gstreamer's pulsesrc and pulsesink which worked. I also tested the following command which also worked:
parec -d alsa_input.usb-041e_30d3_121023000184-00-U0x41e0x30d3.analog-mono | sox -t raw -r 44100 -sLb 16 -c 2 - /home/roos/Arbeitsfläche/pulsetest.wav
and on my second card it worked, too:
parec -d alsa_input.usb-Creative_Technology_Ltd_Sound_Blaster_X-Fi_Go__Pro_00173634-00-Pro_1.analog-stereo | sox -t raw -r 44100 -sLb 16 -c 2 - /home/roos/Arbeitsfläche/pulsetest.wav
Here's the code that's supposed to work:
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <math.h>
#include <pulse/simple.h>
#include <pulse/error.h>
#define BUFSIZE 1024
#define SAMPLE_BITS 16
/* A simple routine calling UNIX write() in a loop */
static ssize_t loop_write(int fd, const uint8_t *data, size_t size)
{
int i = 0;
for (i = 0; i < size; i += 2)
{
// put two bytes into one __signed__ integer
int16_t val = data[i] + ((uint32_t)data[i+1] << 8);
printf("%d", val);
}
return size;
}
int main(int argc, char*argv[])
{
char *device = "alsa_output.usb-Creative_Technology_Ltd_Sound_Blaster_X-Fi_Go__Pro_00173634-00-Pro_1.analog-stereo";
// The sample type to use
static const pa_sample_spec ss = {
.format = PA_SAMPLE_S16LE,
.rate = 44100,
.channels = 2
};
pa_simple *s = NULL;
int ret = 1;
int error;
// Create the recording stream
if (!(s = pa_simple_new(NULL, argv[0], PA_STREAM_RECORD, NULL, "record", &ss, NULL, NULL, &error))) {
fprintf(stderr, __FILE__": pa_simple_new() failed: %s\n", pa_strerror(error));
goto finish;
}
for (;;) {
uint8_t buf[BUFSIZE];
// Record some data ...
if (pa_simple_read(s, buf, sizeof(buf), &error) < 0) {
fprintf(stderr, __FILE__": pa_simple_read() failed: %s\n", pa_strerror(error));
goto finish;
}
// And write it to STDOUT
if (loop_write(STDOUT_FILENO, buf, sizeof(buf)) != sizeof(buf)) {
fprintf(stderr, __FILE__": write() failed: %s\n", strerror(errno));
goto finish;
}
}
ret = 0;
finish:
if (s)
pa_simple_free(s);
return 0;
}
The method "ssize_t loop_write" receives the buffer and because it's a 16 bit little endian byte array I combine two bytes into one singed 16 bit integer. This means the amplitude (represented by the variable "val") should be between 0 and 32768. But as of now it's all 0. So the two main concerns I have are the device source (which imo seems more likely) and my conversion to an integer value.
Do you have any advice on that? Thank you in advance!
EDIT/UPDATE: Ok, I don't know what I did - but if I pass a specific device I'm getting the following message now:
pa_simple_new() failed: Connection refused
When I pass NULL it's working for the default soundcard. Still working with the command line commands I previously described. Any clue what this might be all about?

Answer 1

Ok, just figured it out - quite a silly error made by me.
I passed the device to the first function parameter instead of the fourth.
So do this
if (!(s = pa_simple_new(NULL, argv[0], PA_STREAM_RECORD, device, "record", &ss, NULL, NULL, &error)))
instead of this
if (!(s = pa_simple_new(device, argv[0], PA_STREAM_RECORD, NULL, "record", &ss, NULL, NULL, &error)))