Analyzing Audio Level In Real Time using Python

Question

Im trying to get my Raspberry do stuff, based on the audio level of a played song (sound output). The song shouldn't neccessarily be a local mp3 file on the Raspberry. Let me explain it like this:

If (audio level above threshold): do something..

I've found this http://freshfoo.com/posts/pulseaudio_monitoring/ which is pretty much what im looking for i guess, but i have to be able, reading single samples in order to compare it with thresholds ill be using. Analyze audio using Fast Fourier Transform is also a topic that could help, if there was a code/explanation on how the creater got those numbers. I hope u can help me out with this, for further informations just ask :)

Answer 1

take a look at raspberry-vu project, it's a similar function with the cpu intensive parts written in C. that's fairly important on an RPi.

you can modify the src/impulse.c and src/test-impulse.c to do what you want if you also link in gsl and cblas (dep of gsl) and include <gsl/gsl_statistics_double.h>. you'll notice that you get an array[256] back from im_getSnapshot() which holds the FFT magnitudes. pass that array to your desired function. for me that's sd = gsl_stats_sd(array, 1, 256), and it'll pass back the standard deviation as a simple double. for you, you'll want to use mean = gsl_stats_mean(array, 1, 256) which will give you the average value of all the spectral distribution. you can then do something based on the value of mean.

i'm doing a similar project to suspend/unsuspend an RTP source based on white noise detection (SD is very low for white noise). if the SD is very low, the RTP sink is suspended. otherwise it's enabled. this means a flood of RTP packets only happens when non-whitenoise is found.

this may be your easiest method of reacting to an audio level signal. i've made a snippet here that represents both the stddev and mean of the audio i'm monitoring.

#include <unistd.h>
#include "impulse.h"
#include <stdio.h>
#include <gsl/gsl_statistics_double.h>

int main( ) {
        int i;
        double stddev, stddev_max=0, mean;

        im_start( );

        while ( 1 ) {
                usleep( 1000000 / 10 );
                double *array = im_getSnapshot( IM_FFT );
                for ( i = 0; i < 256; i+=16 )
                {
                        printf( " %.3f,", array[ i ] );
                }

                stddev = gsl_stats_sd(array, 1, 256);
                mean = gsl_stats_mean(array, 1, 256);
                if (stddev > stddev_max)
                    stddev_max = stddev;

                printf("  = [%.05f, %.05f] %.05f\n", stddev, stddev_max, mean);
                fflush( stdout );

                // if (mean > some_value) { do_something(); }
                // else { do_something_else(); }
        }

        im_stop( );

        return 0;
}