Add audio processing examples using Biquad and Biquad Chain

[ruohoruotsi]

Add audio processing examples using Biquad and Biquad Chain, to make it explicit how to integrate the toolkit into an external signal processing chain.

A fully working pd or Max/MSP external would be ideal.

[JoaCHIP]

I agree. The example on how to initialize a lowpass filter is great, but - as a novice C++ coder - I'm having serious trouble figuring out how to apply the filter. Obviously I have to call either BiquadChain::processBiquad or BiquadChain::processFourthOrderSections (which one?) but I cannot figure out the syntax to do so.

[ruohoruotsi]

Ok let me get some examples posted for you, with real audio flowing through, gimme a couple of days!

[yihe1003]

Would you please kindlly post me some examples of audio processing examples using Biquad and Biquad Chain? i want to implement a equalizer using BiquadChain, Thank you so much!

[ruohoruotsi]

Hi there, yes I need to get an example going, I haven't been working on this in a while, but I do have some example code, let me test it out and push a PR for you to look at. thanks for your interest!

[Xueqc]

Would you please kindlly post me some examples of audio processing examples also?

[Xueqc]

Could you point out where am I wrong in following code:

#define BUFFER_LEN 1024
#define MAX_CHANNELS 6

vector <Biquad> coeffs;
BiquadChain biquad_chan;

static void process_data (double *data, int count, int channels)
{
biquad_chan.processBiquad(data, data, 1, count, &coeffs[0]);
return ;
}

static void read_write_file (const char *infilename, const char *outfilename)
{
static double data [BUFFER_LEN] ;
SNDFILE *infile, *outfile ;
SF_INFO sfinfo ;
int readcount ;
memset (&sfinfo, 0, sizeof (sfinfo)) ;

if (! (infile = sf_open (infilename, SFM_READ, &sfinfo)))
{
    printf ("Not able to open input file %s.\n", infilename) ;
    puts (sf_strerror (NULL)) ;
    return;
}

if (sfinfo.channels > MAX_CHANNELS)
{	printf ("Not able to process more than %d channels\n", MAX_CHANNELS) ;
    return;
}
if (! (outfile = sf_open (outfilename, SFM_WRITE, &sfinfo)))
{	printf ("Not able to open output file %s.\n", outfilename) ;
    puts (sf_strerror (NULL)) ;
    return;
}

int filterOrder = 8;
double overallGain = 1.0;

Butterworth butterworth;

bool designedCorrectly = butterworth.loPass(44100,  // fs
    500,
    0,
    filterOrder,
    coeffs,
    overallGain);

biquad_chan.resize(coeffs.size());

while \((readcount = sf_read_double (infile, data, BUFFER_LEN))\)
{	process_data (data, readcount, sfinfo.channels) ;
    sf_write_double (outfile, data, readcount) ;
}
sf_close (infile); sf_close (outfile) ;
return;

}

[Xueqc]

The result wav is noise.

[ruohoruotsi]

Okay, this is an old issue that I previously promised to fix. Let me make an example to share w/ you. I'll also have a look at your code to see what possibly went wrong.

What is the test file that you are using?

[Xueqc]

The test file is your sweep_0_20K.wav