Method and encoder for bit-rate saving encoding of audio signals

摘要

MPEG 1 Audio data compression is based on subband coding. A quantization is performed using a psychoacoustic model which is adapted to the masking behaviour of the human hearing. Each subband signal is quantized in such a way that the quantization noise introduced by the coding will not exceed the masking curve for that subband. In ISO/IEC 11172-3 two independent psychoacoustic models are defined. The output from these psychoacoustic models is a set of Signal-to-Masking Ratios, SMRn, for every subband n. In order to calculate the SMRn for the psychoacoustic model 2 according to the invention a Fast Fourier Transformation (FFT) is performed with a length of L=1152 samples by calculating k subtransformations (ST1,..., ST9) over 2 samples with k*2=L and fitting together (A) the results of the k subtransformations.