Patent ID: 7797155

Claim:
A method of computing perceptual noise in an audio signal, comprising: pre-computing noise values for each critical band within a frame of the audio signal, before entering the quantization loop, as a function of original spectral coefficient values associated with that critical band; pre-computing an excitation value for each critical band before entering the quantization loop, wherein pre-computing the excitation value for each critical band comprises: zeroing out original spectral coefficient values of a current critical band and other critical bands in the frame with spectral coefficient energy less than or equal to spectral coefficient energy of the current critical band; and computing the excitation value of the current critical band as a function of original spectral coefficient values of remaining non-zero critical bands in the frame; and computing an overall perceptual distortion of the frame in the quantization loop, wherein computing the overall perceptual distortion of the frame in the quantization loop comprises: performing quantization on the original spectral coefficients associated with each of the critical bands within the frame to obtain quantized spectral coefficients; performing inverse quantization on the quantized spectral coefficients for each of the critical bands within the frame to obtain reconstructed spectral coefficients; computing a noise to excitation ratio (NER) of each critical band, wherein computing the NER of each critical band comprises: determining whether all the reconstructed spectral coefficients in a critical band are zeroed out due to quantization; if so, computing the NER of that critical band using the pre-computed noise and excitation values associated with that critical band; and if not, computing a new noise value of that critical band as a function of difference between the original spectral coefficient values and reconstructed spectral coefficient values and computing the NER of that critical band using the new noise value and original excitation value associated with the critical band; and computing an overall perceptual distortion of the frame as a sum of NERs of all the critical bands in the frame.