lc3_codec/encoder/
attack_detector.rs

1use crate::common::{
2    complex::Scaler,
3    config::{FrameDuration, Lc3Config},
4};
5const MAX_NUM_DOWNSAMPLED: usize = 160;
6
7// checked against spec
8
9pub struct AttackDetector {
10    // static
11    config: Lc3Config,
12    num_downsampled: usize,
13    num_blocks: usize,
14    attack_pos_limit: i32,
15
16    // mutating state
17    energy_last: Scaler,
18    max_energy_last: Scaler, // last delayed long time temporal envelope
19    attack_pos_last: i32,    // last attack position
20    downsampled_tminus1: i32,
21    downsampled_tminus2: i32,
22}
23
24impl AttackDetector {
25    pub fn new(config: Lc3Config) -> Self {
26        let (num_downsampled, num_blocks, attack_pos_limit) = match config.n_ms {
27            FrameDuration::TenMs => (160, 4, 2),
28            FrameDuration::SevenPointFiveMs => (120, 3, 1),
29        };
30
31        Self {
32            config,
33            max_energy_last: 0.0,
34            energy_last: 0.0,
35            num_downsampled,
36            num_blocks,
37            attack_pos_limit,
38            attack_pos_last: -1,
39            downsampled_tminus1: 0,
40            downsampled_tminus2: 0,
41        }
42    }
43
44    // NOTE that nbytes is the number of bytes of the end compressed audio (not the input audio x_s)
45    pub fn run(&mut self, x_s: &[i16], nbytes: usize) -> bool {
46        assert_eq!(x_s.len(), self.config.nf);
47        if !self.is_active(nbytes) {
48            self.energy_last = 0.0;
49            self.max_energy_last = 0.0;
50            self.attack_pos_last = -1;
51            return false;
52        }
53
54        // downsample into smaller buffer
55        let mut downsampled_buf = [0; MAX_NUM_DOWNSAMPLED];
56        let downsampled = &mut downsampled_buf[..self.num_downsampled];
57        self.downsample(x_s, downsampled);
58
59        // apply highpass filter
60        let mut highpass_buf = [0.0; MAX_NUM_DOWNSAMPLED];
61        let highpass = &mut highpass_buf[..self.num_downsampled];
62        self.filter(downsampled, highpass);
63
64        // record the last 2 downsampled entries for the next frame
65        self.downsampled_tminus1 = downsampled[downsampled.len() - 1];
66        self.downsampled_tminus2 = downsampled[downsampled.len() - 2];
67
68        // energy calculation
69        let mut attack_position = -1;
70        for n in 0..self.num_blocks {
71            let mut energy = 0.0;
72            for hp in highpass[(40 * n)..(40 * n + 40)].iter() {
73                energy += *hp * *hp;
74            }
75            let max_energy = (0.25 * self.max_energy_last).max(self.energy_last);
76
77            // attack detection
78            if energy > 8.5 * max_energy {
79                attack_position = n as i32;
80            }
81
82            self.energy_last = energy;
83            self.max_energy_last = max_energy;
84        }
85
86        let attack_detected = attack_position >= 0 || self.attack_pos_last >= self.attack_pos_limit;
87        self.attack_pos_last = attack_position;
88        attack_detected
89    }
90
91    fn is_active(&self, nbytes: usize) -> bool {
92        if self.config.fs < 32000 {
93            return false;
94        }
95
96        match self.config.n_ms {
97            FrameDuration::SevenPointFiveMs => {
98                (self.config.fs == 32000 && nbytes >= 61 && nbytes < 150)
99                    || (self.config.fs >= 44100 && nbytes >= 75 && nbytes < 150)
100            }
101            FrameDuration::TenMs => {
102                (self.config.fs == 32000 && nbytes > 80) || (self.config.fs >= 41000 && nbytes >= 100)
103            }
104        }
105    }
106
107    fn downsample(&self, input: &[i16], output: &mut [i32]) {
108        let block_len = self.config.nf / self.num_downsampled;
109        for (n, out) in output.iter_mut().enumerate() {
110            // sum all samples in range
111            let from = block_len * n;
112            for input in &input[from..from + block_len] {
113                *out += *input as i32;
114            }
115        }
116    }
117
118    fn filter(&self, input: &[i32], output: &mut [Scaler]) {
119        // note that the first two samples come from the previous frame
120        let tminus1 = self.downsampled_tminus1 as Scaler;
121        let tminus2 = self.downsampled_tminus2 as Scaler;
122        output[0] = 0.375 * input[0] as Scaler - 0.5 * tminus1 + 0.125 * tminus2;
123        output[1] = 0.375 * input[1] as Scaler - 0.5 * input[0] as Scaler + 0.125 * tminus1;
124
125        for (n, output) in output.iter_mut().enumerate().skip(2) {
126            *output = 0.375 * input[n] as Scaler - 0.5 * input[n - 1] as Scaler + 0.125 * input[n - 2] as Scaler;
127        }
128    }
129}
130
131#[cfg(test)]
132mod tests {
133    extern crate std;
134    use super::*;
135    use crate::common::config::{FrameDuration, SamplingFrequency};
136
137    #[test]
138    fn attack_detector_run() {
139        let x_s = [
140            836, 739, 638, 510, 352, 200, 72, -56, -177, -297, -416, -520, -623, -709, -791, -911, -1062, -1199, -1298,
141            -1375, -1433, -1484, -1548, -1603, -1648, -1687, -1724, -1744, -1730, -1699, -1650, -1613, -1594, -1563,
142            -1532, -1501, -1473, -1441, -1409, -1393, -1355, -1280, -1201, -1118, -1032, -953, -860, -741, -613, -477,
143            -355, -261, -168, -80, -8, 57, 127, 217, 296, 347, 385, 413, 456, 517, 575, 640, 718, 806, 888, 963, 1041,
144            1080, 1081, 1083, 1072, 1062, 1067, 1056, 1035, 1019, 999, 964, 934, 909, 876, 854, 835, 813, 795, 781,
145            783, 772, 750, 747, 728, 713, 726, 716, 680, 638, 580, 516, 451, 393, 351, 307, 244, 161, 79, 18, -45,
146            -123, -215, -301, -389, -512, -644, -764, -888, -1006, -1126, -1253, -1378, -1500, -1614, -1716, -1813,
147            -1926, -2051, -2176, -2301, -2416, -2514, -2595, -2680, -2783, -2883, -2977, -3068, -3163, -3262, -3341,
148            -3381, -3392, -3392, -3379, -3368, -3353, -3318, -3292, -3244, -3169, -3109, -3049, -2989, -2922, -2844,
149            -2790, -2743, -2672, -2588, -2490, -2371, -2222, -2046, -1861, -1695, -1546, -1384, -1214, -1058, -913,
150            -761, -602, -441, -280, -124, 24, 169, 302, 421, 546, 661, 738, 796, 851, 924, 1055, 1227, 1412, 1588,
151            1707, 1787, 1853, 1905, 1963, 2015, 2048, 2072, 2082, 2093, 2099, 2095, 2097, 2086, 2063, 2060, 2069, 2052,
152            2012, 1977, 1956, 1948, 1918, 1843, 1748, 1641, 1533, 1435, 1342, 1252, 1163, 1081, 1024, 989, 962, 937,
153            911, 879, 841, 769, 657, 541, 445, 365, 289, 202, 104, -4, -119, -245, -381, -523, -655, -770, -874, -957,
154            -1017, -1069, -1118, -1173, -1256, -1370, -1497, -1629, -1745, -1827, -1882, -1934, -2021, -2115, -2165,
155            -2196, -2230, -2258, -2282, -2302, -2320, -2332, -2340, -2344, -2338, -2313, -2269, -2215, -2152, -2072,
156            -1978, -1885, -1793, -1704, -1621, -1528, -1419, -1310, -1213, -1116, -1014, -914, -820, -736, -656, -578,
157            -514, -445, -358, -276, -206, -136, -62, 0, 56, 124, 190, 253, 316, 379, 458, 552, 630, 686, 725, 735, 709,
158            661, 612, 572, 538, 507, 476, 453, 448, 453, 444, 415, 370, 316, 257, 203, 159, 125, 107, 114, 137, 162,
159            181, 189, 186, 166, 145, 145, 154, 154, 161, 184, 200, 217, 254, 294, 325, 332, 320, 302, 286, 273, 260,
160            266, 294, 297, 274, 251, 221, 170, 100, 29, -31, -82, -134, -187, -232, -278, -347, -426, -490, -548, -613,
161            -677, -727, -755, -769, -770, -757, -741, -729, -713, -684, -659, -647, -631, -606, -588, -585, -577, -555,
162            -534, -527, -528, -513, -480, -456, -440, -415, -382, -333, -244, -132, -32, 47, 130, 225, 308, 383, 460,
163            533, 607, 687, 757, 817, 889, 977, 1038, 1064, 1100, 1165, 1250, 1349, 1456, 1563, 1665, 1755, 1829, 1890,
164            1935, 1973, 2008, 2033, 2044, 2054, 2076, 2106, 2125, 2115, 2097, 2092, 2093, 2082, 2067, 2068, 2095, 2135,
165            2169, 2193, 2213, 2219, 2202, 2163, 2101, 2033, 1992, 1985, 1990, 1986, 1978, 1977, 1976, 1969, 1959, 1956,
166            1960, 1955, 1930, 1907, 1884, 1844, 1790, 1733, 1687, 1649, 1611, 1586,
167        ];
168        let config = Lc3Config::new(SamplingFrequency::Hz48000, FrameDuration::TenMs);
169        let mut detector = AttackDetector::new(config);
170
171        let attack_detected = detector.run(&x_s, 150);
172
173        assert_eq!(detector.max_energy_last, 905588.875);
174        assert_eq!(detector.energy_last, 549861.5);
175        assert_eq!(detector.num_downsampled, 160);
176        assert_eq!(detector.attack_pos_last, 0);
177        assert_eq!(detector.downsampled_tminus1, 4846);
178        assert_eq!(detector.downsampled_tminus2, 5210);
179        assert_eq!(attack_detected, true);
180    }
181}
lc3_codec/encoder/attack_detector.rs

lc3_codec/encoder/
attack_detector.rs
