Representation of spectral envelope with warped frequency resolution for audio coder

We have devised a method for representing frequency spectral envelopes with warped frequency resolution based on sparse non-negative matrices aiming at its use for frequency domain audio coding. With optimally prepared matrices, we can selectively control the resolution of spectral envelopes and enhance the coding efficiency. We show that the devised method can enhance the subjective quality of the state-of-the-art wide-band coder at 16 kbit/s at a cost of minor additional complexity. The method is therefore, expected to be useful for low-bit-rate and low-delay audio coder for mobile communications.