Abstract: Methods and apparatus are disclosed for demonstrating sound quality differences between two sound samples by negatively filtering a first of two signal samples and subsequently representing the negatively filtered signal sample as a first level of sound quality. The second signal sample is represented as a second level of sound quality, typically of higher quality than the first sound sample. The negative filtering is inverse to the enhancement to be demonstrated. In an exemplary embodiment of the invention, negative filtering techniques are used to demonstrate the differences between an "ordinary" voice sample and an "enhanced" voice sample to be broadcast over television or radio facilities. Negative filtering is limited to a selected frequency or range of frequencies such that there is a demonstrable difference in sound quality between the ordinary voice sample and the enhanced voice sample.

Abstract: To prevent particular transmission equipment from artificially increasing low level audio signals to a predetermined allowable level, such signals are first summed with a stabilization signal having a predetermined frequency to form a composite audio signal. Moreover, the stabilization signal has a level that prevents any increase in signal level that may be artificially imposed on the composite signal during the processing of the composite signal by the transmission equipment. Once the composite signal has been so processed, then the stabilization signal is removed therefrom and the original audio signal is outputted to associated transmission media.