Increases the dynamic range of the input audio signal by further reducing (by an adjustable factor) the amplitude of all signals which are below a specified threshold, thereby "expanding" the dynamic range between the low and high amplitude components. A delay buffer is incorporated to give the expander a "look-ahead" capability, improving its effectiveness in some situations. The behaviour of the expander can be adjusted via its Parameter Window as summarised in the following table. Parameter Purpose "Threshold" slider Sets the expander threshold. The purpose of the expander is to modify the amplitude of all signals which are below this threshold. "Ratio" slider Sets the expansion ratio. If the signal amplitude is below the expander threshold, it will be further reduced by this factor (in the dB scale). "Averaging" slider Sets the averaging time for the mean-square level measurement. "Attack" slider Sets the Attack Time for the expander's gain smoother. "Release" slider Sets the Release Time for the expander's gain smoother. "Delay" slider Sets the delay length for the "look-ahead" buffer. "Output Gain" slider Adjusts the amplitude of the output signal, after the expansion has been applied.
The look-ahead expander is implemented by measuring the mean-square level of the audio signal and applying an automatic gain control to a delayed version of the raw signal, where the gain is based on the relative values of the mean-square measurement and the specified threshold and expansion ratio. See [Zo] chapter 7 for a detailed explanation.
