new module bw_bd_reduce (untested)

include/bw_bd_reduce.h

@@ -0,0 +1,164 @@
+/*
+ * Brickworks
+ *
+ * Copyright (C) 2022 Orastron Srl unipersonale
+ *
+ * Brickworks is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3 of the License.
+ *
+ * Brickworks is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Brickworks.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * File author: Stefano D'Angelo
+ */
+
+/*!
+ *  module_type {{{ dsp }}}
+ *  version {{{ 0.3.0 }}}
+ *  requires {{{ bw_config bw_common bw_math }}}
+ *  description {{{
+ *    Bit depth reducer.
+ *
+ *    This is purely an audio effect, it doesn't actually produce an output
+ *    signal with a different encoding. The algorithm is deliberately crude to
+ *    obtain the characteristic noise due to lo-fi A/D quantization.
+ *  }}}
+ *  changelog {{{
+ *    <ul>
+ *      <li>Version <strong>0.3.0</strong>:
+ *        <ul>
+ *          <li>First release.</li>
+ *        </ul>
+ *      </li>
+ *    </ul>
+ *  }}}
+ */
+
+#ifndef _BW_REDUCER_H
+#define _BW_REDUCER_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <bw_common.h>
+
+/*! api {{{
+ *    #### bw_bd_reduce_coeffs
+ *  ```>>> */
+typedef struct _bw_bd_reduce_coeffs bw_bd_reduce_coeffs;
+/*! <<<```
+ *    Coefficients and related.
+ *
+ *    #### bw_bd_reduce_init()
+ *  ```>>> */
+static inline void bw_bd_reduce_init(bw_bd_reduce_coeffs *BW_RESTRICT coeffs);
+/*! <<<```
+ *    Initializes input parameter values in `coeffs`.
+ *
+ *    #### bw_bd_reduce_reset_coeffs()
+ *  ```>>> */
+static inline void bw_bd_reduce_reset_coeffs(bw_bd_reduce_coeffs *BW_RESTRICT coeffs);
+/*! <<<```
+ *    Resets coefficients in `coeffs` to assume their target values.
+ *
+ *    #### bw_bd_reduce_update_coeffs_ctrl()
+ *  ```>>> */
+static inline void bw_bd_reduce_update_coeffs_ctrl(bw_bd_reduce_coeffs *BW_RESTRICT coeffs);
+/*! <<<```
+ *    Triggers control-rate update of coefficients in `coeffs`.
+ *
+ *    #### bw_bd_reduce_update_coeffs_audio()
+ *  ```>>> */
+static inline void bw_bd_reduce_update_coeffs_audio(bw_bd_reduce_coeffs *BW_RESTRICT coeffs);
+/*! <<<```
+ *    Triggers audio-rate update of coefficients in `coeffs`.
+ *
+ *    #### bw_bd_reduce_process1()
+ *  ```>>> */
+static inline float bw_bd_reduce_process1(const bw_bd_reduce_coeffs *BW_RESTRICT coeffs, float x);
+/*! <<<```
+ *    Processes one input sample `x` using `coeffs`. Returns the corresponding
+ *    output sample.
+ *
+ *    #### bw_bd_reduce_process()
+ *  ```>>> */
+static inline void bw_bd_reduce_process(bw_bd_reduce_coeffs *BW_RESTRICT coeffs, const float *x, float* y, int n_samples);
+/*! <<<```
+ *    Processes the first `n_samples` of the input buffer `x` and fills the
+ *    first `n_samples` of the output buffer `y`, while using and updating
+ *    `coeffs` (control and audio rate).
+ *
+ *    #### bw_bd_reduce_set_bit_depth()
+ *  ```>>> */
+static inline void bw_bd_reduce_set_bit_depth(bw_bd_reduce_coeffs *BW_RESTRICT coeffs, char value);
+/*! <<<```
+ *    Sets the output bit depth `value` in `coeffs`. `value` must be strictly positive.
+ *
+ *    Default value: `16`.
+ *  }}} */
+
+/*** Implementation ***/
+
+/* WARNING: This part of the file is not part of the public API. Its content may
+ * change at any time in future versions. Please, do not use it directly. */
+
+#include <bw_math.h>
+
+struct _bw_bd_reduce_coeffs {
+	// Coefficients
+	float	ki;
+	float	k;
+	float	max;
+	
+	// Parameters
+	char	bit_depth;
+	char	bit_depth_prev;
+};
+
+static inline void bw_bd_reduce_init(bw_bd_reduce_coeffs *BW_RESTRICT coeffs) {
+	coeffs->bit_depth = 16;
+}
+
+static inline void bw_bd_reduce_reset_coeffs(bw_bd_reduce_coeffs *BW_RESTRICT coeffs) {
+	coeffs->bit_depth_prev = 0;
+	bw_bd_reduce_update_coeffs_ctrl(coeffs);
+}
+
+static inline void bw_bd_reduce_update_coeffs_ctrl(bw_bd_reduce_coeffs *BW_RESTRICT coeffs) {
+	if (coeffs->bit_depth_prev != coeffs->bit_depth) {
+		coeffs->k = bw_pow2f(coeffs->bit_depth - 1);
+		coeffs->ki = bw_rcpf_2(coeffs->k);
+		coeffs->max = 1.f - 0.5f * coeffs->ki;
+		coeffs->bit_depth_prev = coeffs->bit_depth;
+	}
+}
+
+static inline void bw_bd_reduce_update_coeffs_audio(bw_bd_reduce_coeffs *BW_RESTRICT coeffs) {
+}
+
+static inline float bw_bd_reduce_process1(const bw_bd_reduce_coeffs *BW_RESTRICT coeffs, float x) {
+	return coeffs->ki * (bw_floorf(coeffs->k * bw_clipf(x, -coeffs->max, coeffs->max)) + 0.5f);
+}
+
+static inline void bw_bd_reduce_process(bw_bd_reduce_coeffs *BW_RESTRICT coeffs, const float *x, float* y, int n_samples) {
+	bw_bd_update_coeffs_ctrl(coeffs);
+	for (int i = 0; i < n_samples; i++)
+		y[i] = bw_bd_reduce_process1_scaling(coeffs, x[i]);
+}
+
+static inline void bw_bd_reduce_set_bit_depth(bw_bd_reduce_coeffs *BW_RESTRICT coeffs, char value) {
+	coeffs->bit_depth = value;
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

include/bw_sr_reduce.h

@@ -86,8 +86,8 @@ static inline float bw_sr_reduce_process1(const bw_sr_reduce_coeffs *BW_RESTRICT
 static inline void bw_sr_reduce_process(bw_sr_reduce_coeffs *BW_RESTRICT coeffs, bw_sr_reduce_state *BW_RESTRICT state, const float *x, float* y, int n_samples);
 /*! <<<```
  *    Processes the first `n_samples` of the input buffer `x` and fills the
- *    first `n_samples` of the output buffer `y`, while using and updating both
- *    `coeffs` and `state` (control and audio rate).
+ *    first `n_samples` of the output buffer `y`, while using `coeffs` and
+ *    using and updating `state` (control and audio rate).
  *
  *    #### bw_sr_reduce_set_ratio()
  *  ```>>> */