Direct Digital Synthesis

The dds family of objects enables direct digital up-/down-conversion and resampling as efficiently as possible.

An example of interpolation with the dds_cccf object is listed below.

// direct digital synthesis (dds) interpolation example
#include <liquid/liquid.h>

int main() {
    // options
    float        fc         = -0.2f; // target frequency (relative)
    unsigned int num_stages = 3;     // number of halfband stages
    float        As         = 60.0f; // filter stop-band attenuation [dB]
    float        bw         = 0.25f; // signal bandwidth

    // create object
    dds_cccf q = dds_cccf_create(num_stages,fc,bw,As);

    // execute interpolator and up-converter
    float complex sample_in;
    float complex buf_out[1<<num_stages];
    {
        // initialize with baseband sample here

        // run sample through object
        dds_cccf_interp_execute(q, sample_in, buf_out);
    }

    // destroy object
    dds_cccf_destroy(q);
}

An example of decimation with the dds_cccf object is listed below.

// direct digital synthesis (dds) decimation example
#include <liquid/liquid.h>

int main() {
    // options
    float        fc         = -0.2f; // signal frequency (relative)
    unsigned int num_stages = 3;     // number of halfband stages
    float        As         = 60.0f; // filter stop-band attenuation [dB]
    float        bw         = 0.25f; // signal bandwidth

    // create object
    dds_cccf q = dds_cccf_create(num_stages,fc,bw,As);

    // execute down-converter and decimation
    float complex buf_in[1<<num_stages];
    float complex sample_out;
    {
        // initialize input buffer here

        // pass samples through object
        dds_cccf_decim_execute(q, buf_in, &sample_out);
    }

    // destroy object
    dds_cccf_destroy(q);
}