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Diffstat (limited to 'third_party/libwebrtc/common_audio/signal_processing/splitting_filter.c')
| -rw-r--r-- | third_party/libwebrtc/common_audio/signal_processing/splitting_filter.c | 211 |
1 files changed, 211 insertions, 0 deletions
diff --git a/third_party/libwebrtc/common_audio/signal_processing/splitting_filter.c b/third_party/libwebrtc/common_audio/signal_processing/splitting_filter.c new file mode 100644 index 0000000000..27a0a2a8c9 --- /dev/null +++ b/third_party/libwebrtc/common_audio/signal_processing/splitting_filter.c @@ -0,0 +1,211 @@ +/* + * 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); + } + +} |