mirror of
https://github.com/danog/libtgvoip.git
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5caaaafa42
I'm now using the entire audio processing module from WebRTC as opposed to individual DSP algorithms pulled from there before. Seems to work better this way.
83 lines
3.0 KiB
C
83 lines
3.0 KiB
C
/*
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* Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "common_audio/vad/vad_gmm.h"
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#include "common_audio/signal_processing/include/signal_processing_library.h"
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static const int32_t kCompVar = 22005;
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static const int16_t kLog2Exp = 5909; // log2(exp(1)) in Q12.
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// For a normal distribution, the probability of |input| is calculated and
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// returned (in Q20). The formula for normal distributed probability is
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//
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// 1 / s * exp(-(x - m)^2 / (2 * s^2))
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//
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// where the parameters are given in the following Q domains:
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// m = |mean| (Q7)
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// s = |std| (Q7)
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// x = |input| (Q4)
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// in addition to the probability we output |delta| (in Q11) used when updating
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// the noise/speech model.
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int32_t WebRtcVad_GaussianProbability(int16_t input,
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int16_t mean,
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int16_t std,
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int16_t* delta) {
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int16_t tmp16, inv_std, inv_std2, exp_value = 0;
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int32_t tmp32;
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// Calculate |inv_std| = 1 / s, in Q10.
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// 131072 = 1 in Q17, and (|std| >> 1) is for rounding instead of truncation.
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// Q-domain: Q17 / Q7 = Q10.
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tmp32 = (int32_t) 131072 + (int32_t) (std >> 1);
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inv_std = (int16_t) WebRtcSpl_DivW32W16(tmp32, std);
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// Calculate |inv_std2| = 1 / s^2, in Q14.
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tmp16 = (inv_std >> 2); // Q10 -> Q8.
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// Q-domain: (Q8 * Q8) >> 2 = Q14.
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inv_std2 = (int16_t)((tmp16 * tmp16) >> 2);
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// TODO(bjornv): Investigate if changing to
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// inv_std2 = (int16_t)((inv_std * inv_std) >> 6);
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// gives better accuracy.
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tmp16 = (input << 3); // Q4 -> Q7
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tmp16 = tmp16 - mean; // Q7 - Q7 = Q7
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// To be used later, when updating noise/speech model.
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// |delta| = (x - m) / s^2, in Q11.
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// Q-domain: (Q14 * Q7) >> 10 = Q11.
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*delta = (int16_t)((inv_std2 * tmp16) >> 10);
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// Calculate the exponent |tmp32| = (x - m)^2 / (2 * s^2), in Q10. Replacing
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// division by two with one shift.
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// Q-domain: (Q11 * Q7) >> 8 = Q10.
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tmp32 = (*delta * tmp16) >> 9;
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// If the exponent is small enough to give a non-zero probability we calculate
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// |exp_value| ~= exp(-(x - m)^2 / (2 * s^2))
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// ~= exp2(-log2(exp(1)) * |tmp32|).
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if (tmp32 < kCompVar) {
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// Calculate |tmp16| = log2(exp(1)) * |tmp32|, in Q10.
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// Q-domain: (Q12 * Q10) >> 12 = Q10.
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tmp16 = (int16_t)((kLog2Exp * tmp32) >> 12);
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tmp16 = -tmp16;
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exp_value = (0x0400 | (tmp16 & 0x03FF));
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tmp16 ^= 0xFFFF;
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tmp16 >>= 10;
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tmp16 += 1;
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// Get |exp_value| = exp(-|tmp32|) in Q10.
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exp_value >>= tmp16;
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}
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// Calculate and return (1 / s) * exp(-(x - m)^2 / (2 * s^2)), in Q20.
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// Q-domain: Q10 * Q10 = Q20.
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return inv_std * exp_value;
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}
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