Viennatone GmbH, Frobelgasse 26-32, A-1164 Wien, Austria
In the proposed compression algorithm, Hilbert transform and vector sum generator are used to obtain the Hilbert envelope AM which is the input signal of the following attack/release network (ARN). ARN is simulated by a first-order, low-pass filter with a variable time constant. Signal AM is also processed by a first-order high-pass filter (its time constant is about 10 ms) to provide a signal B for controlling the time constant of the ARN in such a way that the time constant is the attack time with the recommended range from 0.1 to 10 ms when B is positive, and the release time with the recommended range from 10 to 100 ms when B is negative. Finally, a voltage-controlled amplifier is used to amplify the original signal with the gain inversely proportional to the power function of the signal at the output of ARN. The desired compression ratio can be obtained by changing the power. Simulation results have shown that the proposed compression algorithm is simple and applicable for not only the wideband channel, but also multiband channels. In addition, the compression parameters can be adjusted according to the designer's requirement.