A data compression apparatus for compressing a digital input signal to provide a compressed digital output signal. In the apparatus, a circuit derives plural spectral coefficients from the digital input signal, and groups the spectral coefficients into bands. An adaptive bit allocation circuit adaptively allocates a number of spectrum-dependent quantizing bits among the bands to allocate to each band a number of spectrum-dependent quantizing bits for quantizing each of the spectral coefficients in the band. The number of spectrum-dependent quantizing bits allocated to each band by the adaptive bit allocation circuit is determined according to the band magnitude, weighted depending on the band frequency.