254 lines
8.2 KiB
C
254 lines
8.2 KiB
C
/*
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* Brickworks
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*
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* Copyright (C) 2023 Orastron Srl unipersonale
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*
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* Brickworks is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, version 3 of the License.
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*
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* Brickworks is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Brickworks. If not, see <http://www.gnu.org/licenses/>.
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*
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* File author: Stefano D'Angelo
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*/
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/*!
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* module_type {{{ dsp }}}
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* version {{{ 0.5.0 }}}
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* requires {{{ bw_common bw_config bw_math }}}
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* description {{{
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* Aribtrary-ratio IIR sample rate converter.
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* }}}
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* changelog {{{
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* <ul>
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* <li>Version <strong>0.5.0</strong>:
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* <ul>
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* <li>Added <code>bw_src_process_multi()</code>.</li>
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* <li>Added C++ wrapper.</li>
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* </ul>
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* </li>
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* <li>Version <strong>0.4.0</strong>:
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* <ul>
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* <li>First release.</li>
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* </ul>
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* </li>
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* </ul>
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* }}}
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*/
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#ifndef _BW_SRC_H
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#define _BW_SRC_H
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#ifdef __cplusplus
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extern "C" {
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#endif
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#include <bw_common.h>
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/*! api {{{
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* #### bw_src_coeffs
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* ```>>> */
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typedef struct _bw_src_coeffs bw_src_coeffs;
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/*! <<<```
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* Coefficients and related.
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*
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* #### bw_src_state
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* ```>>> */
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typedef struct _bw_src_state bw_src_state;
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/*! <<<```
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* Internal state and related.
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*
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* #### bw_src_init()
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* ```>>> */
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static inline void bw_src_init(bw_src_coeffs *BW_RESTRICT coeffs, float ratio);
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/*! <<<```
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* Initializes `coeffs` using the given resampling `ratio`.
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*
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* `ratio` must be positive and determines the sample rate of the output
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* signal, which will be equal to `ratio` times the sample rate of the input
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* signal.
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*
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* #### bw_src_reset_state()
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* ```>>> */
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static inline void bw_src_reset_state(const bw_src_coeffs *BW_RESTRICT coeffs, bw_src_state *BW_RESTRICT state, float x0);
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/*! <<<```
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* Resets the given `state` to its initial values using the given `coeffs`
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* and the quiescent/initial input value `x0`.
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*
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* #### bw_src_process()
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* ```>>> */
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static inline void bw_src_process(const bw_src_coeffs *BW_RESTRICT coeffs, bw_src_state *BW_RESTRICT state, const float *x, float *y, int *n_in_samples, int *n_out_samples);
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/*! <<<```
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* Processes at most the first `n_in_samples` of the input buffer `x` and
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* fills the output buffer `y` with at most `n_out_samples` using `coeffs`,
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* while using and updating `state`.
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*
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* After the call `n_in_samples` and `n_out_samples` will contain the actual
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* number of consumed input samples and generated output samples,
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* respectively.
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*
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* #### bw_src_process_multi()
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* ```>>> */
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static inline void bw_src_process_multi(const bw_src_coeffs *BW_RESTRICT coeffs, bw_src_state **BW_RESTRICT state, const float **x, float **y, int n_channels, int **n_in_samples, int **n_out_samples);
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/*! <<<```
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* Processes at most the first `n_in_samples[i]` of each input buffer `x[i]`
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* and fills the corresponding output buffer `y[i]` with at most
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* `n_out_samples[i]` using `coeffs`, while using and updating each
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* `state[i]`.
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*
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* After the call each element in `n_in_samples` and `n_out_samples` will
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* contain the actual number of consumed input samples and generated output
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* samples, respectively, for each of the `n_channels` input/output buffer
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* couples.
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* }}} */
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/*** Implementation ***/
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/* WARNING: This part of the file is not part of the public API. Its content may
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* change at any time in future versions. Please, do not use it directly. */
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#include <bw_math.h>
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struct _bw_src_coeffs {
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float k;
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float a1;
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float a2;
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float a3;
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float a4;
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float b0;
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float b1;
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float b2;
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};
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struct _bw_src_state {
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float i;
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float z1;
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float z2;
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float z3;
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float z4;
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float xz1;
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float xz2;
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float xz3;
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};
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static inline void bw_src_init(bw_src_coeffs *BW_RESTRICT coeffs, float ratio) {
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coeffs->k = ratio >= 1.f ? 1.f / ratio : -1.f / ratio;
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// 4th-degree Butterworth with cutoff at ratio * Nyquist, using bilinear transform w/ prewarping
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const float fc = bw_minf(ratio >= 1.f ? 1.f / ratio : ratio, 0.9f);
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const float T = bw_tanf_3(1.570796326794896f * fc);
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const float T2 = T * T;
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const float k = 1.f / (T * (T * (T * (T + 2.613125929752753f) + 3.414213562373095f) + 2.613125929752753f) + 1.f);
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coeffs->b0 = k * T2 * T2;
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coeffs->b1 = 4.f * coeffs->b0;
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coeffs->b2 = 6.f * coeffs->b0;
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coeffs->a1 = k * (T * (T2 * (4.f * T + 5.226251859505504f) - 5.226251859505504f) - 4.f);
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coeffs->a2 = k * (T2 * (6.f * T2 - 6.82842712474619f) + 6.f);
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coeffs->a3 = k * (T * (T2 * (4.f * T - 5.226251859505504f) + 5.226251859505504f) - 4.f);
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coeffs->a4 = k * (T * (T * (T * (T - 2.613125929752753f) + 3.414213562373095f) - 2.613125929752753f) + 1.f);
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}
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static inline void bw_src_reset_state(const bw_src_coeffs *BW_RESTRICT coeffs, bw_src_state *BW_RESTRICT state, float x0) {
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if (coeffs->k < 0) {
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// DF-II
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state->z1 = x0 / (1.f + coeffs->a1 + coeffs->a2 + coeffs->a3 + coeffs->a4);
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state->z2 = state->z1;
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state->z3 = state->z2;
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state->z4 = state->z3;
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} else {
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// TDF-II
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state->z4 = (coeffs->b0 - coeffs->a4) * x0;
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state->z3 = (coeffs->b1 - coeffs->a3) * x0 + state->z4;
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state->z2 = (coeffs->b2 - coeffs->a2) * x0 + state->z3;
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state->z1 = (coeffs->b1 - coeffs->a1) * x0 + state->z2;
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}
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state->i = 0.f;
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state->xz1 = x0;
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state->xz2 = x0;
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state->xz3 = x0;
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}
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static inline void bw_src_process(const bw_src_coeffs *BW_RESTRICT coeffs, bw_src_state *BW_RESTRICT state, const float *x, float *y, int *n_in_samples, int *n_out_samples) {
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int i = 0;
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int j = 0;
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if (coeffs->k < 0) {
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while (i < *n_in_samples && j < *n_out_samples) {
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// DF-II
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const float z0 = x[i] - coeffs->a1 * state->z1 - coeffs->a2 * state->z2 - coeffs->a3 * state->z3 - coeffs->a4 * state->z4;
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const float o = coeffs->b0 * (z0 + state->z4) + coeffs->b1 * (state->z1 + state->z3) + coeffs->b2 * state->z2;
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if (state->i >= 0.f) {
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// 3rd degree Lagrange interpolation + Horner's rule
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const float k1 = state->xz1 - state->xz2;
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const float k2 = 0.333333333333333f * (state->xz3 - o);
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const float k3 = o - k1;
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const float k4 = k3 - state->xz1;
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const float a = k2 - k4 - 0.5f * k4;
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const float b = k3 - k1 - 0.5f * (state->xz1 + state->xz3);
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const float c = 0.5f * (k1 + k2);
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y[j] = o + state->i * (a + state->i * (b + state->i * c));
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state->i += coeffs->k;
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j++;
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}
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state->z4 = state->z3;
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state->z3 = state->z2;
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state->z2 = state->z1;
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state->z1 = z0;
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state->xz3 = state->xz2;
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state->xz2 = state->xz1;
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state->xz1 = o;
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state->i += 1.f;
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i++;
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}
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} else {
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while (i < *n_in_samples && j < *n_out_samples) {
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while (state->i < 1.f && j < *n_out_samples) {
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// 3rd degree Lagrange interpolation + Horner's rule
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const float k1 = state->xz2 - state->xz1;
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const float k2 = 0.333333333333333f * (x[i] - state->xz3);
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const float k3 = state->xz3 - k1;
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const float k4 = state->xz2 - k3;
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const float a = k2 + k4 + 0.5f * k4;
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const float b = k3 - k1 - 0.5f * (x[i] + state->xz2);
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const float c = 0.5f * (k1 + k2);
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const float o = state->xz3 + state->i * (a + state->i * (b + state->i * c));
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// TDF-II
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const float v0 = coeffs->b0 * o;
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const float v1 = coeffs->b1 * o;
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const float v2 = coeffs->b2 * o;
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y[j] = v0 + state->z1;
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state->z1 = v1 - coeffs->a1 * y[j] + state->z2;
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state->z2 = coeffs->b2 * o - coeffs->a2 * y[j] + state->z3;
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state->z3 = v1 - coeffs->a3 * y[j] + state->z4;
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state->z4 = v0 - coeffs->a4 * y[j];
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state->i += coeffs->k;
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j++;
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}
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if (state->i >= 1.f) {
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state->xz3 = state->xz2;
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state->xz2 = state->xz1;
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state->xz1 = x[i];
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state->i -= 1.f;
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i++;
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}
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}
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}
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*n_in_samples = i;
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*n_out_samples = j;
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}
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static inline void bw_src_process_multi(const bw_src_coeffs *BW_RESTRICT coeffs, bw_src_state **BW_RESTRICT state, const float **x, float **y, int n_channels, int **n_in_samples, int **n_out_samples) {
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for (int i = 0; i < n_channels; i++)
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bw_src_process(coeffs, state[i], x[i], y[i], n_in_samples[i], n_out_samples[i]);
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}
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#ifdef __cplusplus
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}
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#endif
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#endif
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