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 /* * 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. */ #include "vad_gmm.h" #include "signal_processing_library.h" #include "typedefs.h" static const int32_t kCompVar = 22005; static const int16_t kLog2Exp = 5909; // log2(exp(1)) in Q12. // For a normal distribution, the probability of |input| is calculated and // returned (in Q20). The formula for normal distributed probability is // // 1 / s * exp(-(x - m)^2 / (2 * s^2)) // // where the parameters are given in the following Q domains: // m = |mean| (Q7) // s = |std| (Q7) // x = |input| (Q4) // in addition to the probability we output |delta| (in Q11) used when updating // the noise/speech model. int32_t WebRtcVad_GaussianProbability(int16_t input, int16_t mean, int16_t std, int16_t* delta) { int16_t tmp16, inv_std, inv_std2, exp_value = 0; int32_t tmp32; // Calculate |inv_std| = 1 / s, in Q10. // 131072 = 1 in Q17, and (|std| >> 1) is for rounding instead of truncation. // Q-domain: Q17 / Q7 = Q10. tmp32 = (int32_t) 131072 + (int32_t) (std >> 1); inv_std = (int16_t) WebRtcSpl_DivW32W16(tmp32, std); // Calculate |inv_std2| = 1 / s^2, in Q14. tmp16 = (inv_std >> 2); // Q10 -> Q8. // Q-domain: (Q8 * Q8) >> 2 = Q14. inv_std2 = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(tmp16, tmp16, 2); // TODO(bjornv): Investigate if changing to // |inv_std2| = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(|inv_std|, |inv_std|, 6); // gives better accuracy. tmp16 = (input << 3); // Q4 -> Q7 tmp16 = tmp16 - mean; // Q7 - Q7 = Q7 // To be used later, when updating noise/speech model. // |delta| = (x - m) / s^2, in Q11. // Q-domain: (Q14 * Q7) >> 10 = Q11. *delta = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(inv_std2, tmp16, 10); // Calculate the exponent |tmp32| = (x - m)^2 / (2 * s^2), in Q10. Replacing // division by two with one shift. // Q-domain: (Q11 * Q7) >> 8 = Q10. tmp32 = WEBRTC_SPL_MUL_16_16_RSFT(*delta, tmp16, 9); // If the exponent is small enough to give a non-zero probability we calculate // |exp_value| ~= exp(-(x - m)^2 / (2 * s^2)) // ~= exp2(-log2(exp(1)) * |tmp32|). if (tmp32 < kCompVar) { // Calculate |tmp16| = log2(exp(1)) * |tmp32|, in Q10. // Q-domain: (Q12 * Q10) >> 12 = Q10. tmp16 = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(kLog2Exp, (int16_t) tmp32, 12); tmp16 = -tmp16; exp_value = (0x0400 | (tmp16 & 0x03FF)); tmp16 ^= 0xFFFF; tmp16 >>= 10; tmp16 += 1; // Get |exp_value| = exp(-|tmp32|) in Q10. exp_value >>= tmp16; } // Calculate and return (1 / s) * exp(-(x - m)^2 / (2 * s^2)), in Q20. // Q-domain: Q10 * Q10 = Q20. return WEBRTC_SPL_MUL_16_16(inv_std, exp_value); }