330 lines
14 KiB
C
330 lines
14 KiB
C
/*
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* Copyright (c) 2012 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_filterbank.h"
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#include "rtc_base/checks.h"
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#include "common_audio/signal_processing/include/signal_processing_library.h"
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// Constants used in LogOfEnergy().
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static const int16_t kLogConst = 24660; // 160*log10(2) in Q9.
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static const int16_t kLogEnergyIntPart = 14336; // 14 in Q10
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// Coefficients used by HighPassFilter, Q14.
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static const int16_t kHpZeroCoefs[3] = { 6631, -13262, 6631 };
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static const int16_t kHpPoleCoefs[3] = { 16384, -7756, 5620 };
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// Allpass filter coefficients, upper and lower, in Q15.
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// Upper: 0.64, Lower: 0.17
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static const int16_t kAllPassCoefsQ15[2] = { 20972, 5571 };
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// Adjustment for division with two in SplitFilter.
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static const int16_t kOffsetVector[6] = { 368, 368, 272, 176, 176, 176 };
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// High pass filtering, with a cut-off frequency at 80 Hz, if the |data_in| is
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// sampled at 500 Hz.
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//
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// - data_in [i] : Input audio data sampled at 500 Hz.
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// - data_length [i] : Length of input and output data.
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// - filter_state [i/o] : State of the filter.
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// - data_out [o] : Output audio data in the frequency interval
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// 80 - 250 Hz.
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static void HighPassFilter(const int16_t* data_in, size_t data_length,
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int16_t* filter_state, int16_t* data_out) {
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size_t i;
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const int16_t* in_ptr = data_in;
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int16_t* out_ptr = data_out;
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int32_t tmp32 = 0;
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// The sum of the absolute values of the impulse response:
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// The zero/pole-filter has a max amplification of a single sample of: 1.4546
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// Impulse response: 0.4047 -0.6179 -0.0266 0.1993 0.1035 -0.0194
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// The all-zero section has a max amplification of a single sample of: 1.6189
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// Impulse response: 0.4047 -0.8094 0.4047 0 0 0
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// The all-pole section has a max amplification of a single sample of: 1.9931
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// Impulse response: 1.0000 0.4734 -0.1189 -0.2187 -0.0627 0.04532
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for (i = 0; i < data_length; i++) {
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// All-zero section (filter coefficients in Q14).
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tmp32 = kHpZeroCoefs[0] * *in_ptr;
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tmp32 += kHpZeroCoefs[1] * filter_state[0];
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tmp32 += kHpZeroCoefs[2] * filter_state[1];
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filter_state[1] = filter_state[0];
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filter_state[0] = *in_ptr++;
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// All-pole section (filter coefficients in Q14).
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tmp32 -= kHpPoleCoefs[1] * filter_state[2];
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tmp32 -= kHpPoleCoefs[2] * filter_state[3];
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filter_state[3] = filter_state[2];
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filter_state[2] = (int16_t) (tmp32 >> 14);
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*out_ptr++ = filter_state[2];
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}
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}
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// All pass filtering of |data_in|, used before splitting the signal into two
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// frequency bands (low pass vs high pass).
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// Note that |data_in| and |data_out| can NOT correspond to the same address.
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//
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// - data_in [i] : Input audio signal given in Q0.
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// - data_length [i] : Length of input and output data.
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// - filter_coefficient [i] : Given in Q15.
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// - filter_state [i/o] : State of the filter given in Q(-1).
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// - data_out [o] : Output audio signal given in Q(-1).
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static void AllPassFilter(const int16_t* data_in, size_t data_length,
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int16_t filter_coefficient, int16_t* filter_state,
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int16_t* data_out) {
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// The filter can only cause overflow (in the w16 output variable)
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// if more than 4 consecutive input numbers are of maximum value and
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// has the the same sign as the impulse responses first taps.
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// First 6 taps of the impulse response:
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// 0.6399 0.5905 -0.3779 0.2418 -0.1547 0.0990
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size_t i;
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int16_t tmp16 = 0;
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int32_t tmp32 = 0;
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int32_t state32 = ((int32_t) (*filter_state) * (1 << 16)); // Q15
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for (i = 0; i < data_length; i++) {
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tmp32 = state32 + filter_coefficient * *data_in;
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tmp16 = (int16_t) (tmp32 >> 16); // Q(-1)
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*data_out++ = tmp16;
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state32 = (*data_in * (1 << 14)) - filter_coefficient * tmp16; // Q14
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state32 *= 2; // Q15.
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data_in += 2;
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}
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*filter_state = (int16_t) (state32 >> 16); // Q(-1)
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}
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// Splits |data_in| into |hp_data_out| and |lp_data_out| corresponding to
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// an upper (high pass) part and a lower (low pass) part respectively.
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//
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// - data_in [i] : Input audio data to be split into two frequency bands.
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// - data_length [i] : Length of |data_in|.
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// - upper_state [i/o] : State of the upper filter, given in Q(-1).
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// - lower_state [i/o] : State of the lower filter, given in Q(-1).
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// - hp_data_out [o] : Output audio data of the upper half of the spectrum.
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// The length is |data_length| / 2.
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// - lp_data_out [o] : Output audio data of the lower half of the spectrum.
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// The length is |data_length| / 2.
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static void SplitFilter(const int16_t* data_in, size_t data_length,
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int16_t* upper_state, int16_t* lower_state,
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int16_t* hp_data_out, int16_t* lp_data_out) {
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size_t i;
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size_t half_length = data_length >> 1; // Downsampling by 2.
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int16_t tmp_out;
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// All-pass filtering upper branch.
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AllPassFilter(&data_in[0], half_length, kAllPassCoefsQ15[0], upper_state,
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hp_data_out);
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// All-pass filtering lower branch.
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AllPassFilter(&data_in[1], half_length, kAllPassCoefsQ15[1], lower_state,
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lp_data_out);
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// Make LP and HP signals.
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for (i = 0; i < half_length; i++) {
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tmp_out = *hp_data_out;
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*hp_data_out++ -= *lp_data_out;
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*lp_data_out++ += tmp_out;
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}
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}
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// Calculates the energy of |data_in| in dB, and also updates an overall
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// |total_energy| if necessary.
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//
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// - data_in [i] : Input audio data for energy calculation.
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// - data_length [i] : Length of input data.
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// - offset [i] : Offset value added to |log_energy|.
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// - total_energy [i/o] : An external energy updated with the energy of
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// |data_in|.
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// NOTE: |total_energy| is only updated if
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// |total_energy| <= |kMinEnergy|.
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// - log_energy [o] : 10 * log10("energy of |data_in|") given in Q4.
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static void LogOfEnergy(const int16_t* data_in, size_t data_length,
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int16_t offset, int16_t* total_energy,
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int16_t* log_energy) {
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// |tot_rshifts| accumulates the number of right shifts performed on |energy|.
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int tot_rshifts = 0;
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// The |energy| will be normalized to 15 bits. We use unsigned integer because
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// we eventually will mask out the fractional part.
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uint32_t energy = 0;
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RTC_DCHECK(data_in);
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RTC_DCHECK_GT(data_length, 0);
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energy = (uint32_t) WebRtcSpl_Energy((int16_t*) data_in, data_length,
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&tot_rshifts);
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if (energy != 0) {
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// By construction, normalizing to 15 bits is equivalent with 17 leading
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// zeros of an unsigned 32 bit value.
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int normalizing_rshifts = 17 - WebRtcSpl_NormU32(energy);
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// In a 15 bit representation the leading bit is 2^14. log2(2^14) in Q10 is
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// (14 << 10), which is what we initialize |log2_energy| with. For a more
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// detailed derivations, see below.
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int16_t log2_energy = kLogEnergyIntPart;
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tot_rshifts += normalizing_rshifts;
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// Normalize |energy| to 15 bits.
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// |tot_rshifts| is now the total number of right shifts performed on
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// |energy| after normalization. This means that |energy| is in
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// Q(-tot_rshifts).
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if (normalizing_rshifts < 0) {
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energy <<= -normalizing_rshifts;
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} else {
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energy >>= normalizing_rshifts;
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}
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// Calculate the energy of |data_in| in dB, in Q4.
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//
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// 10 * log10("true energy") in Q4 = 2^4 * 10 * log10("true energy") =
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// 160 * log10(|energy| * 2^|tot_rshifts|) =
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// 160 * log10(2) * log2(|energy| * 2^|tot_rshifts|) =
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// 160 * log10(2) * (log2(|energy|) + log2(2^|tot_rshifts|)) =
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// (160 * log10(2)) * (log2(|energy|) + |tot_rshifts|) =
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// |kLogConst| * (|log2_energy| + |tot_rshifts|)
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//
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// We know by construction that |energy| is normalized to 15 bits. Hence,
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// |energy| = 2^14 + frac_Q15, where frac_Q15 is a fractional part in Q15.
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// Further, we'd like |log2_energy| in Q10
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// log2(|energy|) in Q10 = 2^10 * log2(2^14 + frac_Q15) =
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// 2^10 * log2(2^14 * (1 + frac_Q15 * 2^-14)) =
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// 2^10 * (14 + log2(1 + frac_Q15 * 2^-14)) ~=
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// (14 << 10) + 2^10 * (frac_Q15 * 2^-14) =
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// (14 << 10) + (frac_Q15 * 2^-4) = (14 << 10) + (frac_Q15 >> 4)
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//
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// Note that frac_Q15 = (|energy| & 0x00003FFF)
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// Calculate and add the fractional part to |log2_energy|.
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log2_energy += (int16_t) ((energy & 0x00003FFF) >> 4);
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// |kLogConst| is in Q9, |log2_energy| in Q10 and |tot_rshifts| in Q0.
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// Note that we in our derivation above have accounted for an output in Q4.
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*log_energy = (int16_t)(((kLogConst * log2_energy) >> 19) +
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((tot_rshifts * kLogConst) >> 9));
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if (*log_energy < 0) {
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*log_energy = 0;
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}
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} else {
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*log_energy = offset;
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return;
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}
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*log_energy += offset;
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// Update the approximate |total_energy| with the energy of |data_in|, if
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// |total_energy| has not exceeded |kMinEnergy|. |total_energy| is used as an
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// energy indicator in WebRtcVad_GmmProbability() in vad_core.c.
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if (*total_energy <= kMinEnergy) {
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if (tot_rshifts >= 0) {
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// We know by construction that the |energy| > |kMinEnergy| in Q0, so add
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// an arbitrary value such that |total_energy| exceeds |kMinEnergy|.
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*total_energy += kMinEnergy + 1;
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} else {
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// By construction |energy| is represented by 15 bits, hence any number of
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// right shifted |energy| will fit in an int16_t. In addition, adding the
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// value to |total_energy| is wrap around safe as long as
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// |kMinEnergy| < 8192.
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*total_energy += (int16_t) (energy >> -tot_rshifts); // Q0.
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}
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}
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}
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int16_t WebRtcVad_CalculateFeatures(VadInstT* self, const int16_t* data_in,
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size_t data_length, int16_t* features) {
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int16_t total_energy = 0;
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// We expect |data_length| to be 80, 160 or 240 samples, which corresponds to
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// 10, 20 or 30 ms in 8 kHz. Therefore, the intermediate downsampled data will
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// have at most 120 samples after the first split and at most 60 samples after
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// the second split.
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int16_t hp_120[120], lp_120[120];
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int16_t hp_60[60], lp_60[60];
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const size_t half_data_length = data_length >> 1;
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size_t length = half_data_length; // |data_length| / 2, corresponds to
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// bandwidth = 2000 Hz after downsampling.
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// Initialize variables for the first SplitFilter().
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int frequency_band = 0;
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const int16_t* in_ptr = data_in; // [0 - 4000] Hz.
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int16_t* hp_out_ptr = hp_120; // [2000 - 4000] Hz.
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int16_t* lp_out_ptr = lp_120; // [0 - 2000] Hz.
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RTC_DCHECK_LE(data_length, 240);
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RTC_DCHECK_LT(4, kNumChannels - 1); // Checking maximum |frequency_band|.
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// Split at 2000 Hz and downsample.
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SplitFilter(in_ptr, data_length, &self->upper_state[frequency_band],
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&self->lower_state[frequency_band], hp_out_ptr, lp_out_ptr);
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// For the upper band (2000 Hz - 4000 Hz) split at 3000 Hz and downsample.
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frequency_band = 1;
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in_ptr = hp_120; // [2000 - 4000] Hz.
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hp_out_ptr = hp_60; // [3000 - 4000] Hz.
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lp_out_ptr = lp_60; // [2000 - 3000] Hz.
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SplitFilter(in_ptr, length, &self->upper_state[frequency_band],
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&self->lower_state[frequency_band], hp_out_ptr, lp_out_ptr);
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// Energy in 3000 Hz - 4000 Hz.
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length >>= 1; // |data_length| / 4 <=> bandwidth = 1000 Hz.
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LogOfEnergy(hp_60, length, kOffsetVector[5], &total_energy, &features[5]);
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// Energy in 2000 Hz - 3000 Hz.
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LogOfEnergy(lp_60, length, kOffsetVector[4], &total_energy, &features[4]);
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// For the lower band (0 Hz - 2000 Hz) split at 1000 Hz and downsample.
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frequency_band = 2;
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in_ptr = lp_120; // [0 - 2000] Hz.
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hp_out_ptr = hp_60; // [1000 - 2000] Hz.
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lp_out_ptr = lp_60; // [0 - 1000] Hz.
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length = half_data_length; // |data_length| / 2 <=> bandwidth = 2000 Hz.
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SplitFilter(in_ptr, length, &self->upper_state[frequency_band],
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&self->lower_state[frequency_band], hp_out_ptr, lp_out_ptr);
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// Energy in 1000 Hz - 2000 Hz.
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length >>= 1; // |data_length| / 4 <=> bandwidth = 1000 Hz.
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LogOfEnergy(hp_60, length, kOffsetVector[3], &total_energy, &features[3]);
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// For the lower band (0 Hz - 1000 Hz) split at 500 Hz and downsample.
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frequency_band = 3;
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in_ptr = lp_60; // [0 - 1000] Hz.
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hp_out_ptr = hp_120; // [500 - 1000] Hz.
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lp_out_ptr = lp_120; // [0 - 500] Hz.
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SplitFilter(in_ptr, length, &self->upper_state[frequency_band],
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&self->lower_state[frequency_band], hp_out_ptr, lp_out_ptr);
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// Energy in 500 Hz - 1000 Hz.
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length >>= 1; // |data_length| / 8 <=> bandwidth = 500 Hz.
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LogOfEnergy(hp_120, length, kOffsetVector[2], &total_energy, &features[2]);
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// For the lower band (0 Hz - 500 Hz) split at 250 Hz and downsample.
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frequency_band = 4;
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in_ptr = lp_120; // [0 - 500] Hz.
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hp_out_ptr = hp_60; // [250 - 500] Hz.
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lp_out_ptr = lp_60; // [0 - 250] Hz.
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SplitFilter(in_ptr, length, &self->upper_state[frequency_band],
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&self->lower_state[frequency_band], hp_out_ptr, lp_out_ptr);
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// Energy in 250 Hz - 500 Hz.
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length >>= 1; // |data_length| / 16 <=> bandwidth = 250 Hz.
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LogOfEnergy(hp_60, length, kOffsetVector[1], &total_energy, &features[1]);
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// Remove 0 Hz - 80 Hz, by high pass filtering the lower band.
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HighPassFilter(lp_60, length, self->hp_filter_state, hp_120);
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// Energy in 80 Hz - 250 Hz.
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LogOfEnergy(hp_120, length, kOffsetVector[0], &total_energy, &features[0]);
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return total_energy;
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}
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