Encoder for encoding an input audio signal comprising signal frames into quantized bits , the encoder comprising: - at least one matrix generation module configured to generate, for each frame of the input audio signal , a signal matrix (103, 203, CovM#1, ..., CovM#N) comprising matrix coefficients obtained from that frame, wherein the signal matrix comprises amplitudes of a frame of the audio signal or is computed based on the amplitudes of the frame of the audio signal; - at least one quantizer module comprising: - a partition module (105, 205, M2V#1, ..., M2V#N) configured to group the matrix coefficients of each signal matrix into a plurality of partition vectors (106, 206, v 1 1 ,... , v L 1 ) , and - a vector quantization module comprising a plurality of vector quantization schemes ( VQ 1 1 , ... , VQ L 1 ) and configured to, for each partition vector (106, 206 , v 1 1 , ... , v L 1 ) , select one of the vector quantization schemes ( VQ 1 1 , ... , VQ L 1 ) and quantize that partition vector according to the selected vector quantization scheme to obtain the quantized bits , wherein, in an adaptive mode, the partition module is able to group differently the matrix coefficients obtained from different frames, and/or the vector quantization module is able to select different vector quantization schemes for partition vectors obtained from different frames. - at least one matrix generation module configured to generate, for each frame of the input audio signal , a signal matrix (103, 203, CovM#1, ..., CovM#N) comprising matrix coefficients obtained from that frame, wherein the signal matrix comprises amplitudes of a frame of the audio signal or is computed based on the amplitudes of the frame of the audio signal; - at least one quantizer module comprising: - a partition module (105, 205, M2V#1, ..., M2V#N) configured to group the matrix coefficients of each signal matrix into a plurality of partition vectors (106, 206, v 1 1 ,... , v L 1 ) , and - a vector quantization module comprising a plurality of vector quantization schemes ( VQ 1 1 , ... , VQ L 1 ) and configured to, for each partition vector (106, 206 , v 1 1 , ... , v L 1 ) , select one of the vector quantization schemes ( VQ 1 1 , ... , VQ L 1 ) and quantize that partition vector according to the selected vector quantization scheme to obtain the quantized bits , wherein, in an adaptive mode, the partition module is able to group differently the matrix coefficients obtained from different frames, and/or the vector quantization module is able to select different vector quantization schemes for partition vectors obtained from different frames. - a partition module (105, 205, M2V#1, ..., M2V#N) configured to group the matrix coefficients of each signal matrix into a plurality of partition vectors (106, 206, v 1 1 ,... , v L 1 ) , and - a vector quantization module comprising a plurality of vector quantization schemes ( VQ 1 1 , ... , VQ L 1 ) and configured to, for each partition vector (106, 206 , v 1 1 , ... , v L 1 ) , select one of the vector quantization schemes ( VQ 1 1 , ... , VQ L 1 ) and quantize that partition vector according to the selected vector quantization scheme to obtain the quantized bits , <EOS>