Abstract
This paper describes a new design method of dynamic range controllers, such as compressor, limiter, expander and noise gate, on a DSP for digital audio systems. For the compressor, we have previously proposed an efficient implementing method on DSP by calculating the polynomial expression to approximate the power transformation. Based on the approximation algorithm, we extend the positive compression ratio to the negative compression ratio for the compressor. Then, we design an expander based on the facts that the ideal compression characteristic could be obtained by application of a polynomial expression. By defining an expansion (downward expansion) characteristic with two threshold levels, the gain for getting the expansion may be decomposed into a gain of an upward expansion with an integer expansion ratio, a gain of a compression and gain shift. By this method, the ideal input-output characteristic can be achieved by using seven-order polynomial expression for dynamic range control of 50dB. The digital signal processing on DSP is about 130 steps for the compressor, and 120 steps for the expander with a given expansion ratio equal to or smaller than 15.
