1/*
2 *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
3 *
4 *  Use of this source code is governed by a BSD-style license
5 *  that can be found in the LICENSE file in the root of the source
6 *  tree. An additional intellectual property rights grant can be found
7 *  in the file PATENTS.  All contributing project authors may
8 *  be found in the AUTHORS file in the root of the source tree.
9 */
10
11/*
12 * This file contains the splitting filter functions.
13 *
14 */
15
16#include "signal_processing_library.h"
17
18// Number of samples in a low/high-band frame.
19enum
20{
21    kBandFrameLength = 160
22};
23
24// QMF filter coefficients in Q16.
25static const WebRtc_UWord16 WebRtcSpl_kAllPassFilter1[3] = {6418, 36982, 57261};
26static const WebRtc_UWord16 WebRtcSpl_kAllPassFilter2[3] = {21333, 49062, 63010};
27
28///////////////////////////////////////////////////////////////////////////////////////////////
29// WebRtcSpl_AllPassQMF(...)
30//
31// Allpass filter used by the analysis and synthesis parts of the QMF filter.
32//
33// Input:
34//    - in_data             : Input data sequence (Q10)
35//    - data_length         : Length of data sequence (>2)
36//    - filter_coefficients : Filter coefficients (length 3, Q16)
37//
38// Input & Output:
39//    - filter_state        : Filter state (length 6, Q10).
40//
41// Output:
42//    - out_data            : Output data sequence (Q10), length equal to
43//                            |data_length|
44//
45
46void WebRtcSpl_AllPassQMF(WebRtc_Word32* in_data, const WebRtc_Word16 data_length,
47                          WebRtc_Word32* out_data, const WebRtc_UWord16* filter_coefficients,
48                          WebRtc_Word32* filter_state)
49{
50    // The procedure is to filter the input with three first order all pass filters
51    // (cascade operations).
52    //
53    //         a_3 + q^-1    a_2 + q^-1    a_1 + q^-1
54    // y[n] =  -----------   -----------   -----------   x[n]
55    //         1 + a_3q^-1   1 + a_2q^-1   1 + a_1q^-1
56    //
57    // The input vector |filter_coefficients| includes these three filter coefficients.
58    // The filter state contains the in_data state, in_data[-1], followed by
59    // the out_data state, out_data[-1]. This is repeated for each cascade.
60    // The first cascade filter will filter the |in_data| and store the output in
61    // |out_data|. The second will the take the |out_data| as input and make an
62    // intermediate storage in |in_data|, to save memory. The third, and final, cascade
63    // filter operation takes the |in_data| (which is the output from the previous cascade
64    // filter) and store the output in |out_data|.
65    // Note that the input vector values are changed during the process.
66    WebRtc_Word16 k;
67    WebRtc_Word32 diff;
68    // First all-pass cascade; filter from in_data to out_data.
69
70    // Let y_i[n] indicate the output of cascade filter i (with filter coefficient a_i) at
71    // vector position n. Then the final output will be y[n] = y_3[n]
72
73    // First loop, use the states stored in memory.
74    // "diff" should be safe from wrap around since max values are 2^25
75    diff = WEBRTC_SPL_SUB_SAT_W32(in_data[0], filter_state[1]); // = (x[0] - y_1[-1])
76    // y_1[0] =  x[-1] + a_1 * (x[0] - y_1[-1])
77    out_data[0] = WEBRTC_SPL_SCALEDIFF32(filter_coefficients[0], diff, filter_state[0]);
78
79    // For the remaining loops, use previous values.
80    for (k = 1; k < data_length; k++)
81    {
82        diff = WEBRTC_SPL_SUB_SAT_W32(in_data[k], out_data[k - 1]); // = (x[n] - y_1[n-1])
83        // y_1[n] =  x[n-1] + a_1 * (x[n] - y_1[n-1])
84        out_data[k] = WEBRTC_SPL_SCALEDIFF32(filter_coefficients[0], diff, in_data[k - 1]);
85    }
86
87    // Update states.
88    filter_state[0] = in_data[data_length - 1]; // x[N-1], becomes x[-1] next time
89    filter_state[1] = out_data[data_length - 1]; // y_1[N-1], becomes y_1[-1] next time
90
91    // Second all-pass cascade; filter from out_data to in_data.
92    diff = WEBRTC_SPL_SUB_SAT_W32(out_data[0], filter_state[3]); // = (y_1[0] - y_2[-1])
93    // y_2[0] =  y_1[-1] + a_2 * (y_1[0] - y_2[-1])
94    in_data[0] = WEBRTC_SPL_SCALEDIFF32(filter_coefficients[1], diff, filter_state[2]);
95    for (k = 1; k < data_length; k++)
96    {
97        diff = WEBRTC_SPL_SUB_SAT_W32(out_data[k], in_data[k - 1]); // =(y_1[n] - y_2[n-1])
98        // y_2[0] =  y_1[-1] + a_2 * (y_1[0] - y_2[-1])
99        in_data[k] = WEBRTC_SPL_SCALEDIFF32(filter_coefficients[1], diff, out_data[k-1]);
100    }
101
102    filter_state[2] = out_data[data_length - 1]; // y_1[N-1], becomes y_1[-1] next time
103    filter_state[3] = in_data[data_length - 1]; // y_2[N-1], becomes y_2[-1] next time
104
105    // Third all-pass cascade; filter from in_data to out_data.
106    diff = WEBRTC_SPL_SUB_SAT_W32(in_data[0], filter_state[5]); // = (y_2[0] - y[-1])
107    // y[0] =  y_2[-1] + a_3 * (y_2[0] - y[-1])
108    out_data[0] = WEBRTC_SPL_SCALEDIFF32(filter_coefficients[2], diff, filter_state[4]);
109    for (k = 1; k < data_length; k++)
110    {
111        diff = WEBRTC_SPL_SUB_SAT_W32(in_data[k], out_data[k - 1]); // = (y_2[n] - y[n-1])
112        // y[n] =  y_2[n-1] + a_3 * (y_2[n] - y[n-1])
113        out_data[k] = WEBRTC_SPL_SCALEDIFF32(filter_coefficients[2], diff, in_data[k-1]);
114    }
115    filter_state[4] = in_data[data_length - 1]; // y_2[N-1], becomes y_2[-1] next time
116    filter_state[5] = out_data[data_length - 1]; // y[N-1], becomes y[-1] next time
117}
118
119void WebRtcSpl_AnalysisQMF(const WebRtc_Word16* in_data, WebRtc_Word16* low_band,
120                           WebRtc_Word16* high_band, WebRtc_Word32* filter_state1,
121                           WebRtc_Word32* filter_state2)
122{
123    WebRtc_Word16 i;
124    WebRtc_Word16 k;
125    WebRtc_Word32 tmp;
126    WebRtc_Word32 half_in1[kBandFrameLength];
127    WebRtc_Word32 half_in2[kBandFrameLength];
128    WebRtc_Word32 filter1[kBandFrameLength];
129    WebRtc_Word32 filter2[kBandFrameLength];
130
131    // Split even and odd samples. Also shift them to Q10.
132    for (i = 0, k = 0; i < kBandFrameLength; i++, k += 2)
133    {
134        half_in2[i] = WEBRTC_SPL_LSHIFT_W32((WebRtc_Word32)in_data[k], 10);
135        half_in1[i] = WEBRTC_SPL_LSHIFT_W32((WebRtc_Word32)in_data[k + 1], 10);
136    }
137
138    // All pass filter even and odd samples, independently.
139    WebRtcSpl_AllPassQMF(half_in1, kBandFrameLength, filter1, WebRtcSpl_kAllPassFilter1,
140                         filter_state1);
141    WebRtcSpl_AllPassQMF(half_in2, kBandFrameLength, filter2, WebRtcSpl_kAllPassFilter2,
142                         filter_state2);
143
144    // Take the sum and difference of filtered version of odd and even
145    // branches to get upper & lower band.
146    for (i = 0; i < kBandFrameLength; i++)
147    {
148        tmp = filter1[i] + filter2[i] + 1024;
149        tmp = WEBRTC_SPL_RSHIFT_W32(tmp, 11);
150        low_band[i] = WebRtcSpl_SatW32ToW16(tmp);
151
152        tmp = filter1[i] - filter2[i] + 1024;
153        tmp = WEBRTC_SPL_RSHIFT_W32(tmp, 11);
154        high_band[i] = WebRtcSpl_SatW32ToW16(tmp);
155    }
156}
157
158void WebRtcSpl_SynthesisQMF(const WebRtc_Word16* low_band, const WebRtc_Word16* high_band,
159                            WebRtc_Word16* out_data, WebRtc_Word32* filter_state1,
160                            WebRtc_Word32* filter_state2)
161{
162    WebRtc_Word32 tmp;
163    WebRtc_Word32 half_in1[kBandFrameLength];
164    WebRtc_Word32 half_in2[kBandFrameLength];
165    WebRtc_Word32 filter1[kBandFrameLength];
166    WebRtc_Word32 filter2[kBandFrameLength];
167    WebRtc_Word16 i;
168    WebRtc_Word16 k;
169
170    // Obtain the sum and difference channels out of upper and lower-band channels.
171    // Also shift to Q10 domain.
172    for (i = 0; i < kBandFrameLength; i++)
173    {
174        tmp = (WebRtc_Word32)low_band[i] + (WebRtc_Word32)high_band[i];
175        half_in1[i] = WEBRTC_SPL_LSHIFT_W32(tmp, 10);
176        tmp = (WebRtc_Word32)low_band[i] - (WebRtc_Word32)high_band[i];
177        half_in2[i] = WEBRTC_SPL_LSHIFT_W32(tmp, 10);
178    }
179
180    // all-pass filter the sum and difference channels
181    WebRtcSpl_AllPassQMF(half_in1, kBandFrameLength, filter1, WebRtcSpl_kAllPassFilter2,
182                         filter_state1);
183    WebRtcSpl_AllPassQMF(half_in2, kBandFrameLength, filter2, WebRtcSpl_kAllPassFilter1,
184                         filter_state2);
185
186    // The filtered signals are even and odd samples of the output. Combine
187    // them. The signals are Q10 should shift them back to Q0 and take care of
188    // saturation.
189    for (i = 0, k = 0; i < kBandFrameLength; i++)
190    {
191        tmp = WEBRTC_SPL_RSHIFT_W32(filter2[i] + 512, 10);
192        out_data[k++] = WebRtcSpl_SatW32ToW16(tmp);
193
194        tmp = WEBRTC_SPL_RSHIFT_W32(filter1[i] + 512, 10);
195        out_data[k++] = WebRtcSpl_SatW32ToW16(tmp);
196    }
197
198}
199