1 /******************************************************************************
2  *
3  *  Copyright 2022 Google LLC
4  *
5  *  Licensed under the Apache License, Version 2.0 (the "License");
6  *  you may not use this file except in compliance with the License.
7  *  You may obtain a copy of the License at:
8  *
9  *  http://www.apache.org/licenses/LICENSE-2.0
10  *
11  *  Unless required by applicable law or agreed to in writing, software
12  *  distributed under the License is distributed on an "AS IS" BASIS,
13  *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14  *  See the License for the specific language governing permissions and
15  *  limitations under the License.
16  *
17  ******************************************************************************/
18 
19 /**
20  * LC3 - Long Term Postfilter
21  *
22  * Reference : Low Complexity Communication Codec (LC3)
23  *             Bluetooth Specification v1.0
24  */
25 
26 #ifndef __LC3_LTPF_H
27 #define __LC3_LTPF_H
28 
29 #include "common.h"
30 #include "bits.h"
31 
32 
33 /**
34  * LTPF data
35  */
36 
37 typedef struct lc3_ltpf_data {
38     bool active;
39     int pitch_index;
40 } lc3_ltpf_data_t;
41 
42 
43 /* ----------------------------------------------------------------------------
44  *  Encoding
45  * -------------------------------------------------------------------------- */
46 
47 /**
48  * LTPF analysis
49  * dt, sr          Duration and samplerate of the frame
50  * ltpf            Context of analysis
51  * allowed         True when activation of LTPF is allowed
52  * x               [-d..-1] Previous, [0..ns-1] Current samples
53  * data            Return bitstream data
54  * return          True when pitch present, False otherwise
55  *
56  * The `x` vector is aligned on 32 bits
57  * The number of previous samples `d` accessed on `x` is :
58  *   d: { 10, 20, 30, 40, 60 } - 1 for samplerates from 8KHz to 48KHz
59  */
60 bool lc3_ltpf_analyse(enum lc3_dt dt, enum lc3_srate sr,
61     lc3_ltpf_analysis_t *ltpf, const int16_t *x, lc3_ltpf_data_t *data);
62 
63 /**
64  * LTPF disable
65  * data            LTPF data, disabled activation on return
66  */
67 void lc3_ltpf_disable(lc3_ltpf_data_t *data);
68 
69 /**
70  * Return number of bits coding the bitstream data
71  * pitch           True when pitch present, False otherwise
72  * return          Bit consumption, including the pitch present flag
73  */
74 int lc3_ltpf_get_nbits(bool pitch);
75 
76 /**
77  * Put bitstream data
78  * bits            Bitstream context
79  * data            LTPF data
80  */
81 void lc3_ltpf_put_data(lc3_bits_t *bits, const lc3_ltpf_data_t *data);
82 
83 
84 /* ----------------------------------------------------------------------------
85  *  Decoding
86  * -------------------------------------------------------------------------- */
87 /**
88  * Get bitstream data
89  * bits            Bitstream context
90  * data            Return bitstream data
91  */
92 void lc3_ltpf_get_data(lc3_bits_t *bits, lc3_ltpf_data_t *data);
93 
94 /**
95  * LTPF synthesis
96  * dt, sr          Duration and samplerate of the frame
97  * nbytes          Size in bytes of the frame
98  * ltpf            Context of synthesis
99  * data            Bitstream data, NULL when pitch not present
100  * xr              Base address of ring buffer of decoded samples
101  * x               Samples to proceed in the ring buffer, filtered as output
102  *
103  * The size of the ring buffer is `nh + ns`.
104  * The filtering needs an history of at least 18 ms.
105  */
106 void lc3_ltpf_synthesize(enum lc3_dt dt, enum lc3_srate sr, int nbytes,
107     lc3_ltpf_synthesis_t *ltpf, const lc3_ltpf_data_t *data,
108     const float *xr, float *x);
109 
110 
111 #endif /* __LC3_LTPF_H */
112