Perceptual Entropy

The term Perceptual Entropy (PE, see [Johnston, 1988]) is used to define the lowest data rate which is needed to encode some audio signal without any perceptual difference to the original. An estimate of the PE (there is not enough theory yet to calculate a real PE) can be used to determine how easy or how difficult it is to encode a given music item using a perceptual coder. 

Brandenburg et al., 1991] Brandenburg, K., Herre, J., Johnston, J. D., Mahieux, Y., and Schroeder, E. F. (1991). ASPEC Adaptive spectral perceptual entropy coding of high quality music signals. In Proc of the 90th. AES-Convention. Preprint 3011. 

Johnston, 1988] Johnston, J. D. (1988). Estimation of perceptual entropy using noise masking criteria. In Proc. IEEE Int. Conf. Acoust., Speech and Signal Proc, pages 2524-2527. 

ASPEC Adaptive spectral perceptual entropy coding. 

In statistical terms, a perceptual improvement is therefore obtained if the amplitude distribution in the filtered signal (image) is more concentrated around zero than in the raw data (contrast enhancement). A more concentrated amplitude distribution generally means smaller entropy. Thus, from an operator perception point of view, interesting results should be obtained if the raw data can be filtered to yield low entropy amplitude distributions. However, one should note that the entropy can be minimized by means of a (pathological) filter which always outputs zero or another constant value. Thus, appropriate restrictions must be imposed on the filter construction process. 

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