AMR is a code-excited linear prediction speech codec, and each 20 ms frame is split into four subframes of 5 ms. A frame’s speech bits hold a small set of parameters. The parameters are not stored in the order listed here: the codec’s encoder sorts bits by perceptual importance (the class A, B and C bits of the frame types) and the order is set by bit tables in 3GPP TS 26.101 and TS 26.201, which are not reproduced here.
AMR
Total bits in each frame, by parameter (summed over all subframes). These add up to each mode’s bit count.
| Mode | Spectral (LSF) | Pitch lag | Fixed codebook | Gains | Total |
|---|---|---|---|---|---|
| 4.75 | 23 | 20 | 36 | 16 | 95 |
| 5.15 | 23 | 20 | 36 | 24 | 103 |
| 5.90 | 26 | 24 | 44 | 24 | 118 |
| 6.70 | 26 | 24 | 56 | 28 | 134 |
| 7.40 | 26 | 26 | 68 | 28 | 148 |
| 7.95 | 27 | 28 | 68 | 36 (16 adaptive + 20 fixed) | 159 |
| 10.2 | 26 | 26 | 124 | 28 | 204 |
| 12.2 | 38 | 30 | 140 | 36 (16 adaptive + 20 fixed) | 244 |
| Parameter | Meaning |
|---|---|
| Spectral | the indices that describe the frame’s line spectral frequencies; 12.2 has five indices for two sets, the others three for one |
| Pitch lag | the adaptive codebook lag, per subframe. The first subframe (and in the higher modes the third) carries an absolute lag; the others are coded relative to it |
| Fixed codebook | the innovation pulses for each subframe |
| Gains | the adaptive and fixed codebook gains; at 12.2 and 7.95 these are separate, and elsewhere they are coded jointly |
AMR-WB
| Mode | VAD | Spectral (ISP) | Pitch lag | LTP filter | Fixed codebook | Gains | High-band gain | Total |
|---|---|---|---|---|---|---|---|---|
| 6.60 | 1 | 36 | 23 | 0 | 48 | 24 | 0 | 132 |
| 8.85 | 1 | 46 | 26 | 0 | 80 | 24 | 0 | 177 |
| 12.65 | 1 | 46 | 30 | 4 | 144 | 28 | 0 | 253 |
| 14.25 | 1 | 46 | 30 | 4 | 176 | 28 | 0 | 285 |
| 15.85 | 1 | 46 | 30 | 4 | 208 | 28 | 0 | 317 |
| 18.25 | 1 | 46 | 30 | 4 | 256 | 28 | 0 | 365 |
| 19.85 | 1 | 46 | 30 | 4 | 288 | 28 | 0 | 397 |
| 23.05 | 1 | 46 | 30 | 4 | 352 | 28 | 0 | 461 |
| 23.85 | 1 | 46 | 30 | 4 | 352 | 28 | 16 | 477 |
| Parameter | Meaning |
|---|---|
| VAD | one bit: voice activity |
| Spectral | the indices of the immittance spectral pair quantiser, seven for most modes and five for 6.60 |
| Pitch lag | the adaptive codebook lag per subframe, with the same relative scheme |
| LTP filter | from 12.65 up: one bit per subframe choosing whether to filter the prediction |
| Fixed codebook | the innovation pulses per subframe |
| Gains | the jointly coded adaptive and innovative gains per subframe |
| High-band gain | only in the 23.85 mode, one 4-bit index per subframe |