1. A method of operating a decoder comprising: obtaining a vector d comprising quantized MDCT domain coefficients of a time segment of an audio signal; deriving a processed vector {circumflex over (d)} by applying a post-filter directly on the vector d, the post-filter being configured to have a transfer function H which is a compressed version of an envelope of the vector d; deriving a signal waveform by performing an inverse MDCT transform on the processed vector {circumflex over (d)}.