1 /* 2 * Copyright (c) 2011 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 #include "vad_gmm.h" 12 13 #include "signal_processing_library.h" 14 #include "typedefs.h" 15 16 static const int32_t kCompVar = 22005; 17 static const int16_t kLog2Exp = 5909; // log2(exp(1)) in Q12. 18 19 // For a normal distribution, the probability of |input| is calculated and 20 // returned (in Q20). The formula for normal distributed probability is 21 // 22 // 1 / s * exp(-(x - m)^2 / (2 * s^2)) 23 // 24 // where the parameters are given in the following Q domains: 25 // m = |mean| (Q7) 26 // s = |std| (Q7) 27 // x = |input| (Q4) 28 // in addition to the probability we output |delta| (in Q11) used when updating 29 // the noise/speech model. 30 int32_t WebRtcVad_GaussianProbability(int16_t input, 31 int16_t mean, 32 int16_t std, 33 int16_t* delta) { 34 int16_t tmp16, inv_std, inv_std2, exp_value = 0; 35 int32_t tmp32; 36 37 // Calculate |inv_std| = 1 / s, in Q10. 38 // 131072 = 1 in Q17, and (|std| >> 1) is for rounding instead of truncation. 39 // Q-domain: Q17 / Q7 = Q10. 40 tmp32 = (int32_t) 131072 + (int32_t) (std >> 1); 41 inv_std = (int16_t) WebRtcSpl_DivW32W16(tmp32, std); 42 43 // Calculate |inv_std2| = 1 / s^2, in Q14. 44 tmp16 = (inv_std >> 2); // Q10 -> Q8. 45 // Q-domain: (Q8 * Q8) >> 2 = Q14. 46 inv_std2 = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(tmp16, tmp16, 2); 47 // TODO(bjornv): Investigate if changing to 48 // |inv_std2| = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(|inv_std|, |inv_std|, 6); 49 // gives better accuracy. 50 51 tmp16 = (input << 3); // Q4 -> Q7 52 tmp16 = tmp16 - mean; // Q7 - Q7 = Q7 53 54 // To be used later, when updating noise/speech model. 55 // |delta| = (x - m) / s^2, in Q11. 56 // Q-domain: (Q14 * Q7) >> 10 = Q11. 57 *delta = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(inv_std2, tmp16, 10); 58 59 // Calculate the exponent |tmp32| = (x - m)^2 / (2 * s^2), in Q10. Replacing 60 // division by two with one shift. 61 // Q-domain: (Q11 * Q7) >> 8 = Q10. 62 tmp32 = WEBRTC_SPL_MUL_16_16_RSFT(*delta, tmp16, 9); 63 64 // If the exponent is small enough to give a non-zero probability we calculate 65 // |exp_value| ~= exp(-(x - m)^2 / (2 * s^2)) 66 // ~= exp2(-log2(exp(1)) * |tmp32|). 67 if (tmp32 < kCompVar) { 68 // Calculate |tmp16| = log2(exp(1)) * |tmp32|, in Q10. 69 // Q-domain: (Q12 * Q10) >> 12 = Q10. 70 tmp16 = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(kLog2Exp, (int16_t) tmp32, 12); 71 tmp16 = -tmp16; 72 exp_value = (0x0400 | (tmp16 & 0x03FF)); 73 tmp16 ^= 0xFFFF; 74 tmp16 >>= 10; 75 tmp16 += 1; 76 // Get |exp_value| = exp(-|tmp32|) in Q10. 77 exp_value >>= tmp16; 78 } 79 80 // Calculate and return (1 / s) * exp(-(x - m)^2 / (2 * s^2)), in Q20. 81 // Q-domain: Q10 * Q10 = Q20. 82 return WEBRTC_SPL_MUL_16_16(inv_std, exp_value); 83 } 84
