dtmf_tone_generator.cc | Explore in Territory

/*
 *  Copyright (c) 2012 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 class provides a generator for DTMF tones. The tone generation is based
// on a sinusoid recursion. Each sinusoid is generated using a recursion
// formula; x[n] = a * x[n-1] - x[n-2], where the coefficient
// a = 2*cos(2*pi*f/fs). The recursion is started with x[-1] = 0 and
// x[-2] = sin(2*pi*f/fs). (Note that with this initialization, the resulting
// sinusoid gets a "negative" rotation; x[n] = sin(-2*pi*f/fs * n + phi), but
// kept this way due to historical reasons.)
// TODO(hlundin): Change to positive rotation?
//
// Each key on the telephone keypad corresponds to an "event", 0-15. Each event
// is mapped to a tone pair, with a low and a high frequency. There are four
// low and four high frequencies, each corresponding to a row and column,
// respectively, on the keypad as illustrated below.
//
//          1209 Hz  1336 Hz  1477 Hz  1633 Hz
// 697 Hz      1        2        3       12
// 770 Hz      4        5        6       13
// 852 Hz      7        8        9       14
// 941 Hz     10        0       11       15

#include "modules/audio_coding/neteq/dtmf_tone_generator.h"

#include "modules/audio_coding/neteq/audio_vector.h"
#include "rtc_base/arraysize.h"
#include "rtc_base/checks.h"

namespace webrtc {

// The filter coefficient a = 2*cos(2*pi*f/fs) for the low frequency tone, for
// sample rates fs = {8000, 16000, 32000, 48000} Hz, and events 0 through 15.
// Values are in Q14.
const int DtmfToneGenerator::kCoeff1[4][16] = …;

// The filter coefficient a = 2*cos(2*pi*f/fs) for the high frequency tone, for
// sample rates fs = {8000, 16000, 32000, 48000} Hz, and events 0 through 15.
// Values are in Q14.
const int DtmfToneGenerator::kCoeff2[4][16] = …;

// The initialization value x[-2] = sin(2*pi*f/fs) for the low frequency tone,
// for sample rates fs = {8000, 16000, 32000, 48000} Hz, and events 0-15.
// Values are in Q14.
const int DtmfToneGenerator::kInitValue1[4][16] = …;

// The initialization value x[-2] = sin(2*pi*f/fs) for the high frequency tone,
// for sample rates fs = {8000, 16000, 32000, 48000} Hz, and events 0-15.
// Values are in Q14.
const int DtmfToneGenerator::kInitValue2[4][16] = …;

// Amplitude multipliers for volume values 0 through 63, corresponding to
// 0 dBm0 through -63 dBm0. Values are in Q14.
// for a in range(0, 64):
//   print round(16141.0 * 10**(-float(a)/20))
const int DtmfToneGenerator::kAmplitude[64] = …;

// Constructor.
DtmfToneGenerator::DtmfToneGenerator()
    : … { … }

// Initialize the DTMF generator with sample rate fs Hz (8000, 16000, 32000,
// 48000), event (0-15) and attenuation (0-36 dB).
// Returns 0 on success, otherwise an error code.
int DtmfToneGenerator::Init(int fs, int event, int attenuation) { … }

// Reset tone generator to uninitialized state.
void DtmfToneGenerator::Reset() { … }

// Generate num_samples of DTMF signal and write to `output`.
int DtmfToneGenerator::Generate(size_t num_samples, AudioMultiVector* output) { … }

bool DtmfToneGenerator::initialized() const { … }

}  // namespace webrtc
chromium/third_party/webrtc/modules/audio_coding/neteq/dtmf_tone_generator.cc
