5.2 Linear prediction analysis and quantization

26.0903GPPAdaptive Multi-Rate (AMR) speech codecMandatory speech CODEC speech processing functionsRelease 17Transcoding functionsTS

12.2 kbit/s mode

Short‑term prediction, or linear prediction (LP), analysis is performed twice per speech frame using the auto‑correlation approach with 30 ms asymmetric windows. No lookahead is used in the auto‑correlation computation.

The auto‑correlations of windowed speech are converted to the LP coefficients using the Levinson‑Durbin algorithm. Then the LP coefficients are transformed to the Line Spectral Pair (LSP) domain for quantization and interpolation purposes. The interpolated quantified and unquantized filter coefficients are converted back to the LP filter coefficients (to construct the synthesis and weighting filters at each subframe).

10.2, 7.95, 7.40, 6.70, 5.90, 5.15, 4.75 kbit/s modes

Short‑term prediction, or linear prediction (LP), analysis is performed once per speech frame using the auto‑correlation approach with 30 ms asymmetric windows. A lookahead of 40 samples (5 ms) is used in the auto‑correlation computation.

The auto‑correlations of windowed speech are converted to the LP coefficients using the Levinson‑Durbin algorithm. Then the LP coefficients are transformed to the Line Spectral Pair (LSP) domain for quantization and interpolation purposes. The interpolated quantified and unquantized filter coefficients are converted back to the LP filter coefficients (to construct the synthesis and weighting filters at each subframe).