Most audio coders developed in recent years make use of psychoacoustics to reduce the data rate required for transmitting or storing digital audio data. These coders are inherently nonlinear and do not pass all of the information applied to them on to their output. This makes evaluation with conventional test techniques difficult and makes the results a poor predictor of audible performance. The presentation will describe continuing work at developing methods for characterizing and comparing low bit-rate coders. A new test method which models the masking characteristics of the auditory system will be described and demonstrated. The technique is implemented on a digital signal processor which computes the masking effects of the test signals on the distortion products created by the coder. The results of measurements on several difference coders will be compared.
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