Re: [LAD] Jack buffer management for block convolution

Am Donnerstag, den 10.06.2010, 23:18 +1000 schrieb Damien Zammit:
> Hi,
>
> I have written a FFTW based block convolution jack client, but I am
> having difficulty processing the last jackframes%L samples of the jack
> buffer. I have read that it might be an idea to collect the samples
> into a second buffer and process them independently of the jack
> process callback, but I have no clue how to implement that. Any
> suggestions would be appreciated.
>
> I want to use the Parks-McClellin algorithm to generate some FIR
> filter coefficents with some user configurable parameters and have it
> process the filters using block convolution. Possibly as an addon for
> calf?
>
> So far my jack client works, and the block convolution overlap-add
> algorithm works as per Oppenheim and Schafer, but the last few samples
> of each jack buffer are zeroes.
>
> It would be nice to be able to have FIR filters longer than the size
> of the jack buffer too. Any ideas?
>
> ---
> Damien Zammit

Hi

here is the implementation I used for a time domaine convolution with a
fixed filter kernel length

inline void convolver_filter(float* input, float* output, int sf,
unsigned int iconvolvefilter)
{
        // select kernel filter
        if (iconvolvefilter >= sizeof(filters) / sizeof(filters[0])) {
                iconvolvefilter = 0;
        }
        // push last samples to the start
        for (int i=0; i < 45; i++) {
                result[i] = result[sf+i];
        }
        // set the rest to zero
        for (int i=45; i < sf+46; i++) {
                result[i] = 0;
        }

// Do convolution:
        for (int i = 0; i < sf; i++) {
                for (int j = 0; j < 45; j++) {
                        result[i+j] += input[i] * filters[iconvolvefilter][j];
                }
        }
        for (int i = 0; i < sf; i++) {
                *output++ = result[i];
        }
}

result[] is a internal buffer with length = jack_buffer_size + kernel
filter length.
sf is the jack_buffer_size.

greats hermann

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Received on Fri Jun 11 12:15:01 2010