1 /* 2 * Copyright (c) 2012 The WebRTC project authors. All Rights Reserved. 3 * 4 * Use of this source code is governed by a BSD-style license 5 * that can be found in the LICENSE file in the root of the source 6 * tree. An additional intellectual property rights grant can be found 7 * in the file PATENTS. All contributing project authors may 8 * be found in the AUTHORS file in the root of the source tree. 9 */ 10 11 // This class provides a generator for DTMF tones. The tone generation is based 12 // on a sinusoid recursion. Each sinusoid is generated using a recursion 13 // formula; x[n] = a * x[n-1] - x[n-2], where the coefficient 14 // a = 2*cos(2*pi*f/fs). The recursion is started with x[-1] = 0 and 15 // x[-2] = sin(2*pi*f/fs). (Note that with this initialization, the resulting 16 // sinusoid gets a "negative" rotation; x[n] = sin(-2*pi*f/fs * n + phi), but 17 // kept this way due to historical reasons.) 18 // TODO(hlundin): Change to positive rotation? 19 // 20 // Each key on the telephone keypad corresponds to an "event", 0-15. Each event 21 // is mapped to a tone pair, with a low and a high frequency. There are four 22 // low and four high frequencies, each corresponding to a row and column, 23 // respectively, on the keypad as illustrated below. 24 // 25 // 1209 Hz 1336 Hz 1477 Hz 1633 Hz 26 // 697 Hz 1 2 3 12 27 // 770 Hz 4 5 6 13 28 // 852 Hz 7 8 9 14 29 // 941 Hz 10 0 11 15 30 31 #include "webrtc/modules/audio_coding/neteq/dtmf_tone_generator.h" 32 33 #include <assert.h> 34 35 namespace webrtc { 36 37 // The filter coefficient a = 2*cos(2*pi*f/fs) for the low frequency tone, for 38 // sample rates fs = {8000, 16000, 32000, 48000} Hz, and events 0 through 15. 39 // Values are in Q14. 40 const int DtmfToneGenerator::kCoeff1[4][16] = { 41 { 24219, 27980, 27980, 27980, 26956, 26956, 26956, 25701, 25701, 25701, 42 24219, 24219, 27980, 26956, 25701, 24219 }, 43 { 30556, 31548, 31548, 31548, 31281, 31281, 31281, 30951, 30951, 30951, 44 30556, 30556, 31548, 31281, 30951, 30556 }, 45 { 32210, 32462, 32462, 32462, 32394, 32394, 32394, 32311, 32311, 32311, 46 32210, 32210, 32462, 32394, 32311, 32210 }, 47 { 32520, 32632, 32632, 32632, 32602, 32602, 32602, 32564, 32564, 32564, 48 32520, 32520, 32632, 32602, 32564, 32520 } }; 49 50 // The filter coefficient a = 2*cos(2*pi*f/fs) for the high frequency tone, for 51 // sample rates fs = {8000, 16000, 32000, 48000} Hz, and events 0 through 15. 52 // Values are in Q14. 53 const int DtmfToneGenerator::kCoeff2[4][16] = { 54 { 16325, 19073, 16325, 13085, 19073, 16325, 13085, 19073, 16325, 13085, 55 19073, 13085, 9315, 9315, 9315, 9315}, 56 { 28361, 29144, 28361, 27409, 29144, 28361, 27409, 29144, 28361, 27409, 57 29144, 27409, 26258, 26258, 26258, 26258}, 58 { 31647, 31849, 31647, 31400, 31849, 31647, 31400, 31849, 31647, 31400, 59 31849, 31400, 31098, 31098, 31098, 31098}, 60 { 32268, 32359, 32268, 32157, 32359, 32268, 32157, 32359, 32268, 32157, 61 32359, 32157, 32022, 32022, 32022, 32022} }; 62 63 // The initialization value x[-2] = sin(2*pi*f/fs) for the low frequency tone, 64 // for sample rates fs = {8000, 16000, 32000, 48000} Hz, and events 0-15. 65 // Values are in Q14. 66 const int DtmfToneGenerator::kInitValue1[4][16] = { 67 { 11036, 8528, 8528, 8528, 9315, 9315, 9315, 10163, 10163, 10163, 11036, 68 11036, 8528, 9315, 10163, 11036}, 69 { 5918, 4429, 4429, 4429, 4879, 4879, 4879, 5380, 5380, 5380, 5918, 5918, 70 4429, 4879, 5380, 5918}, 71 { 3010, 2235, 2235, 2235, 2468, 2468, 2468, 2728, 2728, 2728, 3010, 3010, 72 2235, 2468, 2728, 3010}, 73 { 2013, 1493, 1493, 1493, 1649, 1649, 1649, 1823, 1823, 1823, 2013, 2013, 74 1493, 1649, 1823, 2013 } }; 75 76 // The initialization value x[-2] = sin(2*pi*f/fs) for the high frequency tone, 77 // for sample rates fs = {8000, 16000, 32000, 48000} Hz, and events 0-15. 78 // Values are in Q14. 79 const int DtmfToneGenerator::kInitValue2[4][16] = { 80 { 14206, 13323, 14206, 15021, 13323, 14206, 15021, 13323, 14206, 15021, 81 13323, 15021, 15708, 15708, 15708, 15708}, 82 { 8207, 7490, 8207, 8979, 7490, 8207, 8979, 7490, 8207, 8979, 7490, 8979, 83 9801, 9801, 9801, 9801}, 84 { 4249, 3853, 4249, 4685, 3853, 4249, 4685, 3853, 4249, 4685, 3853, 4685, 85 5164, 5164, 5164, 5164}, 86 { 2851, 2582, 2851, 3148, 2582, 2851, 3148, 2582, 2851, 3148, 2582, 3148, 87 3476, 3476, 3476, 3476} }; 88 89 // Amplitude multipliers for volume values 0 through 36, corresponding to 90 // 0 dBm0 through -36 dBm0. Values are in Q14. 91 const int DtmfToneGenerator::kAmplitude[37] = { 92 16141, 14386, 12821, 11427, 10184, 9077, 8090, 7210, 6426, 5727, 5104, 4549, 93 4054, 3614, 3221, 2870, 2558, 2280, 2032, 1811, 1614, 1439, 1282, 1143, 94 1018, 908, 809, 721, 643, 573, 510, 455, 405, 361, 322, 287, 256 }; 95 96 // Constructor. 97 DtmfToneGenerator::DtmfToneGenerator() 98 : initialized_(false), 99 coeff1_(0), 100 coeff2_(0), 101 amplitude_(0) { 102 } 103 104 // Initialize the DTMF generator with sample rate fs Hz (8000, 16000, 32000, 105 // 48000), event (0-15) and attenuation (0-36 dB). 106 // Returns 0 on success, otherwise an error code. 107 int DtmfToneGenerator::Init(int fs, int event, int attenuation) { 108 initialized_ = false; 109 int fs_index; 110 if (fs == 8000) { 111 fs_index = 0; 112 } else if (fs == 16000) { 113 fs_index = 1; 114 } else if (fs == 32000) { 115 fs_index = 2; 116 } else if (fs == 48000) { 117 fs_index = 3; 118 } else { 119 assert(false); 120 fs_index = 1; // Default to 8000 Hz. 121 } 122 123 if (event < 0 || event > 15) { 124 return kParameterError; // Invalid event number. 125 } 126 127 if (attenuation < 0 || attenuation > 36) { 128 return kParameterError; // Invalid attenuation. 129 } 130 131 // Look up oscillator coefficient for low and high frequencies. 132 coeff1_ = kCoeff1[fs_index][event]; 133 coeff2_ = kCoeff2[fs_index][event]; 134 // Look up amplitude multiplier. 135 amplitude_ = kAmplitude[attenuation]; 136 // Initialize sample history. 137 sample_history1_[0] = kInitValue1[fs_index][event]; 138 sample_history1_[1] = 0; 139 sample_history2_[0] = kInitValue2[fs_index][event]; 140 sample_history2_[1] = 0; 141 142 initialized_ = true; 143 return 0; 144 } 145 146 // Reset tone generator to uninitialized state. 147 void DtmfToneGenerator::Reset() { 148 initialized_ = false; 149 } 150 151 // Generate num_samples of DTMF signal and write to |output|. 152 int DtmfToneGenerator::Generate(int num_samples, 153 AudioMultiVector* output) { 154 if (!initialized_) { 155 return kNotInitialized; 156 } 157 158 if (num_samples < 0 || !output) { 159 return kParameterError; 160 } 161 assert(output->Channels() == 1); // Not adapted for multi-channel yet. 162 if (output->Channels() != 1) { 163 return kStereoNotSupported; 164 } 165 166 output->AssertSize(num_samples); 167 for (int i = 0; i < num_samples; ++i) { 168 // Use recursion formula y[n] = a * y[n - 1] - y[n - 2]. 169 int16_t temp_val_low = ((coeff1_ * sample_history1_[1] + 8192) >> 14) 170 - sample_history1_[0]; 171 int16_t temp_val_high = ((coeff2_ * sample_history2_[1] + 8192) >> 14) 172 - sample_history2_[0]; 173 174 // Update recursion memory. 175 sample_history1_[0] = sample_history1_[1]; 176 sample_history1_[1] = temp_val_low; 177 sample_history2_[0] = sample_history2_[1]; 178 sample_history2_[1] = temp_val_high; 179 180 // Attenuate the low frequency tone 3 dB. 181 int32_t temp_val = kAmpMultiplier * temp_val_low + (temp_val_high << 15); 182 // Normalize the signal to Q14 with proper rounding. 183 temp_val = (temp_val + 16384) >> 15; 184 // Scale the signal to correct volume. 185 (*output)[0][i] = 186 static_cast<int16_t>((temp_val * amplitude_ + 8192) >> 14); 187 } 188 189 return num_samples; 190 } 191 192 } // namespace webrtc 193
