Comodulation masking release in bit‐rate reduction systems

It has been suggested that the level dependence of the upper masking slope be utilized in perceptual models in bit‐rate reduction systems. However, comodulation masking release (CMR) phenomena lead to a reduction of the masking effect when a masker and a probe signal are amplitude modulated with the same frequency. In bit‐rate reduction systems the masker would be the audio signal and the probe signal would represent the quantization noise. Masking curves have been determined for sinusoids and 1‐Bark‐wide noise maskers in order to investigate the risk of CMR, when quantizing depths are fixed in accordance with psycho‐acoustical principles. Masker frequencies of 500 Hz, 1 kHz, and 2 kHz have been investigated, and the masking of pure tone probes has been determined in the first four 1/3 octaves above the masker. Modulation frequencies between 6 and 20 Hz were used with a modulation depth of 0.75. A CMR of up to 10 dB was obtained at a distance of 6 Bark above the masker. The amount of CMR was found to depe...