Audio encoder and decoder

Abstract

The present document relates an audio encoding and decoding system (referred to as an audio codec system). In particular, the present document relates to a transform-based audio codec system which is particularly well suited for voice encoding/decoding. A transform-based speech encoder () configured to encode a speech signal into a bitstream is described. The encoder () comprises a framing unit () configured to receive a set () of blocks; wherein the set () of blocks comprises a plurality of sequential blocks () of transform coefficients; wherein the plurality of blocks () is indicative of samples of the speech signal; wherein a block () of transform coefficients comprises a plurality of transform coefficients for a corresponding plurality of frequency bins (). Furthermore, the encoder () comprises an envelope estimation unit () configured to determine a current envelope () based on the plurality of sequential blocks () of transform coefficients; wherein the current envelope () is indicative of a plurality of spectral energy values () for the corresponding plurality of frequency bins (). In addition, the encoder () comprises an envelope interpolation unit () configured to determine a plurality of interpolated envelopes () for the plurality of blocks () of transform coefficients, respectively, based on the current envelope (); Furthermore, the encoder () comprises a flattening unit () configured to determine a plurality of blocks () of flattened transform coefficients by flattening the corresponding plurality of blocks () of transform coefficients using the corresponding plurality of interpolated envelopes (), respectively; wherein the bitstream is determined based on the plurality of blocks () of flattened transform coefficients.