chromium/third_party/webrtc/common_audio/signal_processing/resample_fractional.c

/*
 *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */


/*
 * This file contains the resampling functions between 48, 44, 32 and 24 kHz.
 * The description headers can be found in signal_processing_library.h
 *
 */

#include "common_audio/signal_processing/include/signal_processing_library.h"

// interpolation coefficients
static const int16_t kCoefficients48To32[2][8] = …;

static const int16_t kCoefficients32To24[3][8] = …;

static const int16_t kCoefficients44To32[4][9] = …;

//   Resampling ratio: 2/3
// input:  int32_t (normalized, not saturated) :: size 3 * K
// output: int32_t (shifted 15 positions to the left, + offset 16384) :: size 2 * K
//      K: number of blocks

void WebRtcSpl_Resample48khzTo32khz(const int32_t *In, int32_t *Out, size_t K)
{ … }

//   Resampling ratio: 3/4
// input:  int32_t (normalized, not saturated) :: size 4 * K
// output: int32_t (shifted 15 positions to the left, + offset 16384) :: size 3 * K
//      K: number of blocks

void WebRtcSpl_Resample32khzTo24khz(const int32_t *In, int32_t *Out, size_t K)
{ … }

//
// fractional resampling filters
//   Fout = 11/16 * Fin
//   Fout =  8/11 * Fin
//

// compute two inner-products and store them to output array
static void WebRtcSpl_ResampDotProduct(const int32_t *in1, const int32_t *in2,
                                       const int16_t *coef_ptr, int32_t *out1,
                                       int32_t *out2)
{ … }

//   Resampling ratio: 8/11
// input:  int32_t (normalized, not saturated) :: size 11 * K
// output: int32_t (shifted 15 positions to the left, + offset 16384) :: size  8 * K
//      K: number of blocks

void WebRtcSpl_Resample44khzTo32khz(const int32_t *In, int32_t *Out, size_t K)
{ … }