dsps_resampler_ph.c File Reference

#include "dsps_resampler.h"
#include <math.h>

Include dependency graph for dsps_resampler_ph.c:

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Functions
esp_err_t	dsps_resampler_ph_init (dsps_resample_ph_t *resampler, float samplerate_factor)
	Initialize the poly-phase resampler.
int32_t	dsps_resampler_ph_exec (dsps_resample_ph_t *resampler, float *input, float *output, int32_t length)
	Execute the poly-phase resampler.

Function Documentation

dsps_resampler_ph_exec()

int32_t dsps_resampler_ph_exec	(	dsps_resample_ph_t *	resampler,
		float *	input,
		float *	output,
		int32_t	length )

Execute the poly-phase resampler.

Parameters

resampler	Pointer to the resampler structure
input	Pointer to the input buffer
output	Pointer to the output buffer
length	Length of the input buffer

Returns

Length of the output buffer

Definition at line 28 of file dsps_resampler_ph.c.

{
    int32_t result = 0;
    int input_pos = 0;
    float in_x[4];
 
    int in_pos = 0;
    for (int pos = resampler->delay_pos; pos < 4; pos++) {
        in_x[in_pos++] = resampler->delay[pos];
    }
    for (int pos = 0; pos < resampler->delay_pos; pos++) {
        in_x[in_pos++] = resampler->delay[pos];
    }
 
    while (input_pos < length) {
 
        float c0 = in_x[1];
        float c1 = 0.5 * (in_x[2] - in_x[0]);
        float c2 = in_x[0] - 2.5 * in_x[1] + 2 * in_x[2] - 0.5 * in_x[3];
        float c3 = 0.5 * (in_x[3] - in_x[0]) + 1.5 * (in_x[1] - in_x[2]);
 
        output[result] = c0 + resampler->phase * (c1 + resampler->phase * (c2 + resampler->phase * c3));
        result++;
        resampler->phase += resampler->step;
 
        while (resampler->phase >= 1) {
            resampler->phase -= 1;
            resampler->delay[resampler->delay_pos] = input[input_pos];
            resampler->delay_pos++;
            if (resampler->delay_pos >= 4) {
                resampler->delay_pos = 0;
            }
            input_pos++;
            in_pos = 0;
            for (int pos = resampler->delay_pos; pos < 4; pos++) {
                in_x[in_pos++] = resampler->delay[pos];
            }
            for (int pos = 0; pos < resampler->delay_pos; pos++) {
                in_x[in_pos++] = resampler->delay[pos];
            }
        }
    }
 
    return result;
}

References dsps_resample_ph_s::delay, dsps_resample_ph_s::delay_pos, dsps_resample_ph_s::phase, and dsps_resample_ph_s::step.

dsps_resampler_ph_init()

esp_err_t dsps_resampler_ph_init	(	dsps_resample_ph_t *	resampler,
		float	samplerate_factor )

Initialize the poly-phase resampler.

The poly-phase resampler is a implementation of the poly-phase Farrow filter that use cubic interpolation with 4 coefficients.

Parameters

resampler	Pointer to the resampler structure
samplerate_factor	Sample rate factor

Returns

ESP_OK on success, ESP_ERR_INVALID_ARG if the parameters are invalid

Definition at line 10 of file dsps_resampler_ph.c.

{
    esp_err_t ret = ESP_OK;
 
    if (samplerate_factor < 1) {
        return ESP_ERR_DSP_INVALID_PARAM;
    }
 
    for (int i = 0; i < 4; i++) {
        resampler->delay[i] = 0;
    }
    resampler->delay_pos = 0;
 
    resampler->step = 1.0f / samplerate_factor;
    resampler->phase = 0;
    return ret;
}

References dsps_resample_ph_s::delay, dsps_resample_ph_s::delay_pos, ESP_ERR_DSP_INVALID_PARAM, ESP_OK, dsps_resample_ph_s::phase, and dsps_resample_ph_s::step.