An Open Source Stereo Widening Plugin
Stereo widening algorithms aim to extend the stereo image width and thereby, increase the perceived spaciousness of a mix. Here, we present the design and implementation of a stereo widening plugin that is computationally efficient. First, a stereo signal is decorrelated by convolving with a velvet noise sequence, or alternately, by passing through a cascade of allpass filters with randomised phase. Both the original and decorrelated signals are passed through perfect reconstruction filterbanks to get a set of lowpassed and highpassed signals. Then, the original and decorrelated filtered signals are combined through a mixer and summed to produce the final stereo output. Two separate parameters control the perceived width of the lower frequencies and higher frequencies respectively. A transient detection block prevents the smearing of percussive signals caused by the decorrelation filters. The stereo widener has been released as an open-source plugin.