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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.
*/
/*
* This file contains the splitting filter functions.
*
*/
#include "rtc_base/checks.h"
#include "common_audio/signal_processing/include/signal_processing_library.h"
// Maximum number of samples in a low/high-band frame.
enum
{
kMaxBandFrameLength = 320 // 10 ms at 64 kHz.
};
// QMF filter coefficients in Q16.
static const uint16_t WebRtcSpl_kAllPassFilter1[3] = {6418, 36982, 57261};
static const uint16_t WebRtcSpl_kAllPassFilter2[3] = {21333, 49062, 63010};
///////////////////////////////////////////////////////////////////////////////////////////////
// WebRtcSpl_AllPassQMF(...)
//
// Allpass filter used by the analysis and synthesis parts of the QMF filter.
//
// Input:
// - in_data : Input data sequence (Q10)
// - data_length : Length of data sequence (>2)
// - filter_coefficients : Filter coefficients (length 3, Q16)
//
// Input & Output:
// - filter_state : Filter state (length 6, Q10).
//
// Output:
// - out_data : Output data sequence (Q10), length equal to
// |data_length|
//
static void WebRtcSpl_AllPassQMF(int32_t* in_data,
size_t data_length,
int32_t* out_data,
const uint16_t* filter_coefficients,
int32_t* filter_state)
{
// The procedure is to filter the input with three first order all pass filters
// (cascade operations).
//
// a_3 + q^-1 a_2 + q^-1 a_1 + q^-1
// y[n] = ----------- ----------- ----------- x[n]
// 1 + a_3q^-1 1 + a_2q^-1 1 + a_1q^-1
//
// The input vector |filter_coefficients| includes these three filter coefficients.
// The filter state contains the in_data state, in_data[-1], followed by
// the out_data state, out_data[-1]. This is repeated for each cascade.
// The first cascade filter will filter the |in_data| and store the output in
// |out_data|. The second will the take the |out_data| as input and make an
// intermediate storage in |in_data|, to save memory. The third, and final, cascade
// filter operation takes the |in_data| (which is the output from the previous cascade
// filter) and store the output in |out_data|.
// Note that the input vector values are changed during the process.
size_t k;
int32_t diff;
// First all-pass cascade; filter from in_data to out_data.
// Let y_i[n] indicate the output of cascade filter i (with filter coefficient a_i) at
// vector position n. Then the final output will be y[n] = y_3[n]
// First loop, use the states stored in memory.
// "diff" should be safe from wrap around since max values are 2^25
// diff = (x[0] - y_1[-1])
diff = WebRtcSpl_SubSatW32(in_data[0], filter_state[1]);
// y_1[0] = x[-1] + a_1 * (x[0] - y_1[-1])
out_data[0] = WEBRTC_SPL_SCALEDIFF32(filter_coefficients[0], diff, filter_state[0]);
// For the remaining loops, use previous values.
for (k = 1; k < data_length; k++)
{
// diff = (x[n] - y_1[n-1])
diff = WebRtcSpl_SubSatW32(in_data[k], out_data[k - 1]);
// y_1[n] = x[n-1] + a_1 * (x[n] - y_1[n-1])
out_data[k] = WEBRTC_SPL_SCALEDIFF32(filter_coefficients[0], diff, in_data[k - 1]);
}
// Update states.
filter_state[0] = in_data[data_length - 1]; // x[N-1], becomes x[-1] next time
filter_state[1] = out_data[data_length - 1]; // y_1[N-1], becomes y_1[-1] next time
// Second all-pass cascade; filter from out_data to in_data.
// diff = (y_1[0] - y_2[-1])
diff = WebRtcSpl_SubSatW32(out_data[0], filter_state[3]);
// y_2[0] = y_1[-1] + a_2 * (y_1[0] - y_2[-1])
in_data[0] = WEBRTC_SPL_SCALEDIFF32(filter_coefficients[1], diff, filter_state[2]);
for (k = 1; k < data_length; k++)
{
// diff = (y_1[n] - y_2[n-1])
diff = WebRtcSpl_SubSatW32(out_data[k], in_data[k - 1]);
// y_2[0] = y_1[-1] + a_2 * (y_1[0] - y_2[-1])
in_data[k] = WEBRTC_SPL_SCALEDIFF32(filter_coefficients[1], diff, out_data[k-1]);
}
filter_state[2] = out_data[data_length - 1]; // y_1[N-1], becomes y_1[-1] next time
filter_state[3] = in_data[data_length - 1]; // y_2[N-1], becomes y_2[-1] next time
// Third all-pass cascade; filter from in_data to out_data.
// diff = (y_2[0] - y[-1])
diff = WebRtcSpl_SubSatW32(in_data[0], filter_state[5]);
// y[0] = y_2[-1] + a_3 * (y_2[0] - y[-1])
out_data[0] = WEBRTC_SPL_SCALEDIFF32(filter_coefficients[2], diff, filter_state[4]);
for (k = 1; k < data_length; k++)
{
// diff = (y_2[n] - y[n-1])
diff = WebRtcSpl_SubSatW32(in_data[k], out_data[k - 1]);
// y[n] = y_2[n-1] + a_3 * (y_2[n] - y[n-1])
out_data[k] = WEBRTC_SPL_SCALEDIFF32(filter_coefficients[2], diff, in_data[k-1]);
}
filter_state[4] = in_data[data_length - 1]; // y_2[N-1], becomes y_2[-1] next time
filter_state[5] = out_data[data_length - 1]; // y[N-1], becomes y[-1] next time
}
void WebRtcSpl_AnalysisQMF(const int16_t* in_data, size_t in_data_length,
int16_t* low_band, int16_t* high_band,
int32_t* filter_state1, int32_t* filter_state2)
{
size_t i;
int16_t k;
int32_t tmp;
int32_t half_in1[kMaxBandFrameLength];
int32_t half_in2[kMaxBandFrameLength];
int32_t filter1[kMaxBandFrameLength];
int32_t filter2[kMaxBandFrameLength];
const size_t band_length = in_data_length / 2;
RTC_DCHECK_EQ(0, in_data_length % 2);
RTC_DCHECK_LE(band_length, kMaxBandFrameLength);
// Split even and odd samples. Also shift them to Q10.
for (i = 0, k = 0; i < band_length; i++, k += 2)
{
half_in2[i] = ((int32_t)in_data[k]) * (1 << 10);
half_in1[i] = ((int32_t)in_data[k + 1]) * (1 << 10);
}
// All pass filter even and odd samples, independently.
WebRtcSpl_AllPassQMF(half_in1, band_length, filter1,
WebRtcSpl_kAllPassFilter1, filter_state1);
WebRtcSpl_AllPassQMF(half_in2, band_length, filter2,
WebRtcSpl_kAllPassFilter2, filter_state2);
// Take the sum and difference of filtered version of odd and even
// branches to get upper & lower band.
for (i = 0; i < band_length; i++)
{
tmp = (filter1[i] + filter2[i] + 1024) >> 11;
low_band[i] = WebRtcSpl_SatW32ToW16(tmp);
tmp = (filter1[i] - filter2[i] + 1024) >> 11;
high_band[i] = WebRtcSpl_SatW32ToW16(tmp);
}
}
void WebRtcSpl_SynthesisQMF(const int16_t* low_band, const int16_t* high_band,
size_t band_length, int16_t* out_data,
int32_t* filter_state1, int32_t* filter_state2)
{
int32_t tmp;
int32_t half_in1[kMaxBandFrameLength];
int32_t half_in2[kMaxBandFrameLength];
int32_t filter1[kMaxBandFrameLength];
int32_t filter2[kMaxBandFrameLength];
size_t i;
int16_t k;
RTC_DCHECK_LE(band_length, kMaxBandFrameLength);
// Obtain the sum and difference channels out of upper and lower-band channels.
// Also shift to Q10 domain.
for (i = 0; i < band_length; i++)
{
tmp = (int32_t)low_band[i] + (int32_t)high_band[i];
half_in1[i] = tmp * (1 << 10);
tmp = (int32_t)low_band[i] - (int32_t)high_band[i];
half_in2[i] = tmp * (1 << 10);
}
// all-pass filter the sum and difference channels
WebRtcSpl_AllPassQMF(half_in1, band_length, filter1,
WebRtcSpl_kAllPassFilter2, filter_state1);
WebRtcSpl_AllPassQMF(half_in2, band_length, filter2,
WebRtcSpl_kAllPassFilter1, filter_state2);
// The filtered signals are even and odd samples of the output. Combine
// them. The signals are Q10 should shift them back to Q0 and take care of
// saturation.
for (i = 0, k = 0; i < band_length; i++)
{
tmp = (filter2[i] + 512) >> 10;
out_data[k++] = WebRtcSpl_SatW32ToW16(tmp);
tmp = (filter1[i] + 512) >> 10;
out_data[k++] = WebRtcSpl_SatW32ToW16(tmp);
}
}