Backward-compatible integration of harmonic transposer for high frequency reconstruction of audio signals
A method for decoding an encoded audio bitstream is disclosed. The method includes receiving the encoded audio bitstream and decoding the audio data to generate a decoded lowband audio signal. The method further includes extracting high frequency reconstruction metadata and filtering the decoded lowband audio signal with an analysis filterbank to generate a filtered lowband audio signal. The method also includes extracting a flag indicating whether either spectral translation or harmonic transposition is to be performed on the audio data and regenerating a highband portion of the audio signal using the filtered lowband audio signal and the high frequency reconstruction metadata in accordance with the flag.
1. A method for decoding an encoded audio bitstream, the method comprising:
receiving the encoded audio bitstream, the encoded audio bitstream including audio data representing a lowband portion of an audio signal;
decoding the audio data to generate a decoded lowband audio signal;
extracting from the encoded audio bitstream high frequency reconstruction metadata, the high frequency reconstruction metadata including operating parameters for a high frequency reconstruction process that linearly translates a consecutive number of subbands from a lowband portion of the audio signal to a highband portion of the audio signal;
filtering the decoded lowband audio signal with an analysis filterbank to generate a filtered lowband audio signal;
extracting from the encoded audio bitstream a flag indicating whether either linear translation or harmonic transposition is to be performed on the audio data;
regenerating a highband portion of the audio signal using the filtered lowband audio signal and the high frequency reconstruction metadata in accordance with the flag; and
combining the filtered lowband audio signal and the regenerated highband portion to form a wideband audio signal,
wherein the analysis filterbank includes analysis filters, h k (n), that are modulated versions of a prototype filter, p 0 (n), according to:
h
k
(
n
)
=
p
0
(
n
)
exp
{
i
π
M
(
k
+
1
2
)
(
n
-
N
2
)
}
,
0
≤
n
≤
N
;
0
≤
k
<
M
where p 0 (n) is a real-valued symmetric or asymmetric prototype filter, M is a number of channels in the analysis filterbank and N is the prototype filter order.
2. The method of claim 1 wherein the high frequency reconstruction metadata includes an operating parameter selected from the group consisting of envelope scalefactors, noise floor scale factors, sinusoid addition information, time/frequency grid information, crossover frequency, and inverse filtering mode.
3. The method of claim 1 wherein the prototype filter, p 0 (n), is derived from coefficients of Table 4 below:
TABLE 4
n
p 0 (n)
0
0.0000000000
1
−0.0005525286
2
−0.0005617692
3
−0.0004947518
4
−0.0004875227
5
−0.0004893791
6
−0.0005040714
7
−0.0005226564
8
−0.0005466565
9
−0.0005677802
10
−0.0005870930
11
−0.0006132747
12
−0.0006312493
13
−0.0006540333
14
−0.0006777690
15
−0.0006941614
16
−0.0007157736
17
−0.0007255043
18
−0.0007440941
19
−0.0007490598
20
−0.0007681371
21
−0.0007724848
22
−0.0007834332
23
−0.0007779869
24
−0.0007803664
25
−0.0007801449
26
−0.0007757977
27
−0.0007630793
28
−0.0007530001
29
−0.0007319357
30
−0.0007215391
31
−0.0006917937
32
−0.0006650415
33
−0.0006341594
34
−0.0005946118
35
−0.0005564576
36
−0.0005145572
37
−0.0004606325
38
−0.0004095121
39
−0.0003501175
40
−0.0002896981
41
−0.0002098337
42
−0.0001446380
43
−0.0000617334
44
0.0000134949
45
0.0001094383
46
0.0002043017
47
0.0002949531
48
0.0004026540
49
0.0005107388
50
0.0006239376
51
0.0007458025
52
0.0008608443
53
0.0009885988
54
0.0011250155
55
0.0012577884
56
0.0013902494
57
0.0015443219
58
0.0016868083
59
0.0018348265
60
0.0019841140
61
0.0021461583
62
0.0023017254
63
0.0024625616
64
0.0026201758
65
0.0027870464
66
0.0029469447
67
0.0031125420
68
0.0032739613
69
0.0034418874
70
0.0036008268
71
0.0037603922
72
0.0039207432
73
0.0040819753
74
0.0042264269
75
0.0043730719
76
0.0045209852
77
0.0046606460
78
0.0047932560
79
0.0049137603
80
0.0050393022
81
0.0051407353
82
0.0052461166
83
0.0053471681
84
0.0054196775
85
0.0054876040
86
0.0055475714
87
0.0055938023
88
0.0056220643
89
0.0056455196
90
0.0056389199
91
0.0056266114
92
0.0055917128
93
0.0055404363
94
0.0054753783
95
0.0053838975
96
0.0052715758
97
0.0051382275
98
0.0049839687
99
0.0048109469
100
0.0046039530
101
0.0043801861
102
0.0041251642
103
0.0038456408
104
0.0035401246
105
0.0032091885
106
0.0028446757
107
0.0024508540
108
0.0020274176
109
0.0015784682
110
0.0010902329
111
0.0005832264
112
0.0000276045
113
−0.0005464280
114
−0.0011568135
115
−0.0018039472
116
−0.0024826723
117
−0.0031933778
118
−0.0039401124
119
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120
−0.0055337211
121
−0.0063792293
122
−0.0072615816
123
−0.0081798233
124
−0.0091325329
125
−0.0101150215
126
−0.0111315548
127
−0.0121849995
128
0.0132718220
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0.0143904666
130
0.0155405553
131
0.0167324712
132
0.0179433381
133
0.0191872431
134
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135
0.0217467550
136
0.0230680169
137
0.0244160992
138
0.0257875847
139
0.0271859429
140
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141
0.0300502657
142
0.0315017608
143
0.0329754081
144
0.0344620948
145
0.0359697560
146
0.0374812850
147
0.0390053679
148
0.0405349170
149
0.0420649094
150
0.0436097542
151
0.0451488405
152
0.0466843027
153
0.0482165720
154
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155
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0.0542452768
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159
0.0571616450
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0.0585915683
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0.0599837480
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0.0613455171
163
0.0626857808
164
0.0639715898
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0.0652247106
166
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167
0.0676075985
168
0.0687043828
169
0.0697630244
170
0.0707628710
171
0.0717002673
172
0.0725682583
173
0.0733620255
174
0.0741003642
175
0.0747452558
176
0.0753137336
177
0.0758008358
178
0.0761992479
179
0.0764992170
180
0.0767093490
181
0.0768173975
182
0.0768230011
183
0.0767204924
184
0.0765050718
185
0.0761748321
186
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0.0744664394
189
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190
0.0726774642
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194
0.0674525021
195
0.0657690668
196
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197
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199
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200
0.0550460034
201
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202
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204
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205
0.0401458278
206
0.0366418116
207
0.0329583930
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209
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211
0.0163701258
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216
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218
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221
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226
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227
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228
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229
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230
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232
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235
−0.1459766491
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−0.1549607071
237
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239
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240
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241
−0.2021250176
242
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244
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245
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246
−0.2526480309
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−0.2631053299
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−0.2736634040
249
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312
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313
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339
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380
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382
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384
−0.3611589903
385
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467
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468
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469
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470
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471
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472
0.0687043828
473
0.0676075985
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476
0.0639715898
477
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481
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482
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−0.0039401124
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533
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534
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0.0043730719
566
0.0042264269
567
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568
0.0039207432
569
0.0037603922
570
0.0036008268
571
0.0034418874
572
0.0032739613
573
0.0031125420
574
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0.0027870464
576
0.0026201758
577
0.0024625616
578
0.0023017254
579
0.0021461583
580
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581
0.0018348265
582
0.0016868083
583
0.0015443219
584
0.0013902494
585
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586
0.0011250155
587
0.0009885988
588
0.0008608443
589
0.0007458025
590
0.0006239376
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0.0005107388
592
0.0004026540
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599
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609
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610
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614
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615
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618
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619
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620
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621
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622
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623
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624
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625
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626
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627
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628
−0.0006312493
629
−0.0006132747
630
−0.0005870930
631
−0.0005677802
632
−0.0005466565
633
−0.0005226564
634
−0.0005040714
635
−0.0004893791
636
−0.0004875227
637
−0.0004947518
638
−0.0005617692
639
−0.0005525280.
.
4. The method of claim 3 wherein the prototype filter, p 0 (n), is derived from the coefficients of Table 4 by one or more mathematical operations selected from the group consisting of rounding, subsampling, interpolation, or decimation.
5. A non-transitory computer readable medium containing instructions that when executed by a processor perform the method of claim 1 .
6. A decoder for decoding an encoded audio bitstream, the decoder comprising:
an input interface for receiving the encoded audio bitstream, the encoded audio bitstream including audio data representing a lowband portion of an audio signal;
a core decoder for decoding the audio data to generate a decoded lowband audio signal;
a deformatter for extracting from the encoded audio bitstream high frequency reconstruction metadata, the high frequency reconstruction metadata including operating parameters for a high frequency reconstruction process that linearly translates a consecutive number of subbands from a lowband portion of the audio signal to a highband portion of the audio signal;
an analysis filterbank for filtering the decoded lowband audio signal to generate a filtered lowband audio signal;
a deformatter for extracting from the encoded audio bitstream a flag indicating whether either linear translation or harmonic transposition is to be performed on the audio data;
a high frequency regenerator for regenerating a highband portion of the audio signal using the filtered lowband audio signal and the high frequency reconstruction metadata in accordance with the flag; and
a synthesis filterbank for combining the filtered lowband audio signal and the regenerated highband portion to form a wideband audio signal,
wherein the analysis filterbank includes analysis filters, h k (n), that are modulated versions of a prototype filter, p 0 (n), according to:
h
k
(
n
)
=
p
0
(
n
)
exp
{
i
π
M
(
k
+
1
2
)
(
n
-
n
2
)
}
,
0
≤
n
≤
N
;
0
≤
k
<
M
where p 0 (n) is a real-valued symmetric or asymmetric prototype filter, M is a number of channels in the analysis filterbank and N is the prototype filter order.
7. The decoder of claim 6 wherein wherein the high frequency reconstruction metadata includes an operating parameter selected from the group consisting of envelope scalefactors, noise floor scale factors, sinusoid addition information, time/frequency grid information, crossover frequency, and inverse filtering mode.
8. The decoder of claim 6 wherein the prototype filter, p 0 (n), is derived from coefficients of Table 4 below:
TABLE 4
n
p 0 (n)
0
0.0000000000
1
−0.0005525286
2
−0.0005617692
3
−0.0004947518
4
−0.0004875227
5
−0.0004893791
6
−0.0005040714
7
−0.0005226564
8
−0.0005466565
9
−0.0005677802
10
−0.0005870930
11
−0.0006132747
12
−0.0006312493
13
−0.0006540333
14
−0.0006777690
15
−0.0006941614
16
−0.0007157736
17
−0.0007255043
18
−0.0007440941
19
−0.0007490598
20
−0.0007681371
21
−0.0007724848
22
−0.0007834332
23
−0.0007779869
24
−0.0007803664
25
−0.0007801449
26
−0.0007757977
27
−0.0007630793
28
−0.0007530001
29
−0.0007319357
30
−0.0007215391
31
−0.0006917937
32
−0.0006650415
33
−0.0006341594
34
−0.0005946118
35
−0.0005564576
36
−0.0005145572
37
−0.0004606325
38
−0.0004095121
39
−0.0003501175
40
−0.0002896981
41
−0.0002098337
42
−0.0001446380
43
−0.0000617334
44
0.0000134949
45
0.0001094383
46
0.0002043017
47
0.0002949531
48
0.0004026540
49
0.0005107388
50
0.0006239376
51
0.0007458025
52
0.0008608443
53
0.0009885988
54
0.0011250155
55
0.0012577884
56
0.0013902494
57
0.0015443219
58
0.0016868083
59
0.0018348265
60
0.0019841140
61
0.0021461583
62
0.0023017254
63
0.0024625616
64
0.0026201758
65
0.0027870464
66
0.0029469447
67
0.0031125420
68
0.0032739613
69
0.0034418874
70
0.0036008268
71
0.0037603922
72
0.0039207432
73
0.0040819753
74
0.0042264269
75
0.0043730719
76
0.0045209852
77
0.0046606460
78
0.0047932560
79
0.0049137603
80
0.0050393022
81
0.0051407353
82
0.0052461166
83
0.0053471681
84
0.0054196775
85
0.0054876040
86
0.0055475714
87
0.0055938023
88
0.0056220643
89
0.0056455196
90
0.0056389199
91
0.0056266114
92
0.0055917128
93
0.0055404363
94
0.0054753783
95
0.0053838975
96
0.0052715758
97
0.0051382275
98
0.0049839687
99
0.0048109469
100
0.0046039530
101
0.0043801861
102
0.0041251642
103
0.0038456408
104
0.0035401246
105
0.0032091885
106
0.0028446757
107
0.0024508540
108
0.0020274176
109
0.0015784682
110
0.0010902329
111
0.0005832264
112
0.0000276045
113
−0.0005464280
114
−0.0011568135
115
−0.0018039472
116
−0.0024826723
117
−0.0031933778
118
−0.0039401124
119
−0.0047222596
120
−0.0055337211
121
−0.0063792293
122
−0.0072615816
123
−0.0081798233
124
−0.0091325329
125
−0.0101150215
126
−0.0111315548
127
−0.0121849995
128
0.0132718220
129
0.0143904666
130
0.0155405553
131
0.0167324712
132
0.0179433381
133
0.0191872431
134
0.0204531793
135
0.0217467550
136
0.0230680169
137
0.0244160992
138
0.0257875847
139
0.0271859429
140
0.0286072173
141
0.0300502657
142
0.0315017608
143
0.0329754081
144
0.0344620948
145
0.0359697560
146
0.0374812850
147
0.0390053679
148
0.0405349170
149
0.0420649094
150
0.0436097542
151
0.0451488405
152
0.0466843027
153
0.0482165720
154
0.0497385755
155
0.0512556155
156
0.0527630746
157
0.0542452768
158
0.0557173648
159
0.0571616450
160
0.0585915683
161
0.0599837480
162
0.0613455171
163
0.0626857808
164
0.0639715898
165
0.0652247106
166
0.0664367512
167
0.0676075985
168
0.0687043828
169
0.0697630244
170
0.0707628710
171
0.0717002673
172
0.0725682583
173
0.0733620255
174
0.0741003642
175
0.0747452558
176
0.0753137336
177
0.0758008358
178
0.0761992479
179
0.0764992170
180
0.0767093490
181
0.0768173975
182
0.0768230011
183
0.0767204924
184
0.0765050718
185
0.0761748321
186
0.0757305756
187
0.0751576255
188
0.0744664394
189
0.0736406005
190
0.0726774642
191
0.0715826364
192
0.0703533073
193
0.0689664013
194
0.0674525021
195
0.0657690668
196
0.0639444805
197
0.0619602779
198
0.0598166570
199
0.0575152691
200
0.0550460034
201
0.0524093821
202
0.0495978676
203
0.0466303305
204
0.0434768782
205
0.0401458278
206
0.0366418116
207
0.0329583930
208
0.0290824006
209
0.0250307561
210
0.0207997072
211
0.0163701258
212
0.0117623832
213
0.0069636862
214
0.0019765601
215
−0.0032086896
216
−0.0085711749
217
−0.0141288827
218
−0.0198834129
219
−0.0258227288
220
−0.0319531274
221
−0.0382776572
222
−0.0447806821
223
−0.0514804176
224
−0.0583705326
225
−0.0654409853
226
−0.0726943300
227
−0.0801372934
228
−0.0877547536
229
−0.0955533352
230
−0.1035329531
231
−0.1116826931
232
−0.1200077984
233
−0.1285002850
234
−0.1371551761
235
−0.1459766491
236
−0.1549607071
237
−0.1640958855
238
−0.1733808172
239
−0.1828172548
240
−0.1923966745
241
−0.2021250176
242
−0.2119735853
243
−0.2219652696
244
−0.2320690870
245
−0.2423016884
246
−0.2526480309
247
−0.2631053299
248
−0.2736634040
249
−0.2843214189
250
−0.2950716717
251
−0.3059098575
252
−0.3168278913
253
−0.3278113727
254
−0.3388722693
255
−0.3499914122
256
0.3611589903
257
0.3723795546
258
0.3836350013
259
0.3949211761
260
0.4062317676
261
0.4175696896
262
0.4289119920
263
0.4402553754
264
0.4515996535
265
0.4629308085
266
0.4742453214
267
0.4855253091
268
0.4967708254
269
0.5079817500
270
0.5191234970
271
0.5302240895
272
0.5412553448
273
0.5522051258
274
0.5630789140
275
0.5738524131
276
0.5845403235
277
0.5951123086
278
0.6055783538
279
0.6159109932
280
0.6261242695
281
0.6361980107
282
0.6461269695
283
0.6559016302
284
0.6655139880
285
0.6749663190
286
0.6842353293
287
0.6933282376
288
0.7022388719
289
0.7109410426
290
0.7194462634
291
0.7277448900
292
0.7358211758
293
0.7436827863
294
0.7513137456
295
0.7587080760
296
0.7658674865
297
0.7727780881
298
0.7794287519
299
0.7858353120
300
0.7919735841
301
0.7978466413
302
0.8034485751
303
0.8087695004
304
0.8138191270
305
0.8185776004
306
0.8230419890
307
0.8272275347
308
0.8311038457
309
0.8346937361
310
0.8379717337
311
0.8409541392
312
0.8436238281
313
0.8459818469
314
0.8480315777
315
0.8497805198
316
0.8511971524
317
0.8523047035
318
0.8531020949
319
0.8535720573
320
0.8537385600
321
0.8535720573
322
0.8531020949
323
0.8523047035
324
0.8511971524
325
0.8497805198
326
0.8480315777
327
0.8459818469
328
0.8436238281
329
0.8409541392
330
0.8379717337
331
0.8346937361
332
0.8311038457
333
0.8272275347
334
0.8230419890
335
0.8185776004
336
0.8138191270
337
0.8087695004
338
0.8034485751
339
0.7978466413
340
0.7919735841
341
0.7858353120
342
0.7794287519
343
0.7727780881
344
0.7658674865
345
0.7587080760
346
0.7513137456
347
0.7436827863
348
0.7358211758
349
0.7277448900
350
0.7194462634
351
0.7109410426
352
0.7022388719
353
0.6933282376
354
0.6842353293
355
0.6749663190
356
0.6655139880
357
0.6559016302
358
0.6461269695
359
0.6361980107
360
0.6261242695
361
0.6159109932
362
0.6055783538
363
0.5951123086
364
0.5845403235
365
0.5738524131
366
0.5630789140
367
0.5522051258
368
0.5412553448
369
0.5302240895
370
0.5191234970
371
0.5079817500
372
0.4967708254
373
0.4855253091
374
0.4742453214
375
0.4629308085
376
0.4515996535
377
0.4402553754
378
0.4289119920
379
0.4175696896
380
0.4062317676
381
0.3949211761
382
0.3836350013
383
0.3723795546
384
−0.3611589903
385
−0.3499914122
386
−0.3388722693
387
−0.3278113727
388
−0.3168278913
389
−0.3059098575
390
−0.2950716717
391
−0.2843214189
392
−0.2736634040
393
−0.2631053299
394
−0.2526480309
395
−0.2423016884
396
−0.2320690870
397
−0.2219652696
398
−0.2119735853
399
−0.2021250176
400
−0.1923966745
401
−0.1828172548
402
−0.1733808172
403
−0.1640958855
404
−0.1549607071
405
−0.1459766491
406
−0.1371551761
407
−0.1285002850
408
−0.1200077984
409
−0.1116826931
410
−0.1035329531
411
−0.0955533352
412
−0.0877547536
413
−0.0801372934
414
−0.0726943300
415
−0.0654409853
416
−0.0583705326
417
−0.0514804176
418
−0.0447806821
419
−0.0382776572
420
−0.0319531274
421
−0.0258227288
422
−0.0198834129
423
−0.0141288827
424
−0.0085711749
425
−0.0032086896
426
0.0019765601
427
0.0069636862
428
0.0117623832
429
0.0163701258
430
0.0207997072
431
0.0250307561
432
0.0290824006
433
0.0329583930
434
0.0366418116
435
0.0401458278
436
0.0434768782
437
0.0466303305
438
0.0495978676
439
0.0524093821
440
0.0550460034
441
0.0575152691
442
0.0598166570
443
0.0619602779
444
0.0639444805
445
0.0657690668
446
0.0674525021
447
0.0689664013
448
0.0703533073
449
0.0715826364
450
0.0726774642
451
0.0736406005
452
0.0744664394
453
0.0751576255
454
0.0757305756
455
0.0761748321
456
0.0765050718
457
0.0767204924
458
0.0768230011
459
0.0768173975
460
0.0767093490
461
0.0764992170
462
0.0761992479
463
0.0758008358
464
0.0753137336
465
0.0747452558
466
0.0741003642
467
0.0733620255
468
0.0725682583
469
0.0717002673
470
0.0707628710
471
0.0697630244
472
0.0687043828
473
0.0676075985
474
0.0664367512
475
0.0652247106
476
0.0639715898
477
0.0626857808
478
0.0613455171
479
0.0599837480
480
0.0585915683
481
0.0571616450
482
0.0557173648
483
0.0542452768
484
0.0527630746
485
0.0512556155
486
0.0497385755
487
0.0482165720
488
0.0466843027
489
0.0451488405
490
0.0436097542
491
0.0420649094
492
0.0405349170
493
0.0390053679
494
0.0374812850
495
0.0359697560
496
0.0344620948
497
0.0329754081
498
0.0315017608
499
0.0300502657
500
0.0286072173
501
0.0271859429
502
0.0257875847
503
0.0244160992
504
0.0230680169
505
0.0217467550
506
0.0204531793
507
0.0191872431
508
0.0179433381
509
0.0167324712
510
0.0155405553
511
0.0143904666
512
−0.0132718220
513
−0.0121849995
514
−0.0111315548
515
−0.0101150215
516
−0.0091325329
517
−0.0081798233
518
−0.0072615816
519
−0.0063792293
520
−0.0055337211
521
−0.0047222596
522
−0.0039401124
523
−0.0031933778
524
−0.0024826723
525
−0.0018039472
526
−0.0011568135
527
−0.0005464280
528
0.0000276045
529
0.0005832264
530
0.0010902329
531
0.0015784682
532
0.0020274176
533
0.0024508540
534
0.0028446757
535
0.0032091885
536
0.0035401246
537
0.0038456408
538
0.0041251642
539
0.0043801861
540
0.0046039530
541
0.0048109469
542
0.0049839687
543
0.0051382275
544
0.0052715758
545
0.0053838975
546
0.0054753783
547
0.0055404363
548
0.0055917128
549
0.0056266114
550
0.0056389199
551
0.0056455196
552
0.0056220643
553
0.0055938023
554
0.0055475714
555
0.0054876040
556
0.0054196775
557
0.0053471681
558
0.0052461166
559
0.0051407353
560
0.0050393022
561
0.0049137603
562
0.0047932560
563
0.0046606460
564
0.0045209852
565
0.0043730719
566
0.0042264269
567
0.0040819753
568
0.0039207432
569
0.0037603922
570
0.0036008268
571
0.0034418874
572
0.0032739613
573
0.0031125420
574
0.0029469447
575
0.0027870464
576
0.0026201758
577
0.0024625616
578
0.0023017254
579
0.0021461583
580
0.0019841140
581
0.0018348265
582
0.0016868083
583
0.0015443219
584
0.0013902494
585
0.0012577884
586
0.0011250155
587
0.0009885988
588
0.0008608443
589
0.0007458025
590
0.0006239376
591
0.0005107388
592
0.0004026540
593
0.0002949531
594
0.0002043017
595
0.0001094383
596
0.0000134949
597
−0.0000617334
598
−0.0001446380
599
−0.0002098337
600
−0.0002896981
601
−0.0003501175
602
−0.0004095121
603
−0.0004606325
604
−0.0005145572
605
−0.0005564576
606
−0.0005946118
607
−0.0006341594
608
−0.0006650415
609
−0.0006917937
610
−0.0007215391
611
−0.0007319357
612
−0.0007530001
613
−0.0007630793
614
−0.0007757977
615
−0.0007801449
616
−0.0007803664
617
−0.0007779869
618
−0.0007834332
619
−0.0007724848
620
−0.0007681371
621
−0.0007490598
622
−0.0007440941
623
−0.0007255043
624
−0.0007157736
625
−0.0006941614
626
−0.0006777690
627
−0.0006540333
628
−0.0006312493
629
−0.0006132747
630
−0.0005870930
631
−0.0005677802
632
−0.0005466565
633
−0.0005226564
634
−0.0005040714
635
−0.0004893791
636
−0.0004875227
637
−0.0004947518
638
−0.0005617692
639
−0.0005525280.
.
9. The decoder of claim 8 wherein the prototype filter, p 0 (n), is derived from the coefficients of Table 4 by one or more mathematical operations selected from the group consisting of rounding, subsampling, interpolation, or decimation.