16th June 2005
Wahwactor is a two-input and one-output system. Out of the two input tracks, one of the tracks may be considered a control rather than a proper input since it is the one in charge of driving the transformations to be applied to the audio signal. In the context of the Wahwactor, the audio signal is typically a guitar signal and the control signal is a voice saying "wa-wa".
First, the voice signal is analyzed to pick up a meaningful descriptor that, after a simple conversion (shift, scale and smooth), is used as the centre frequency of the wah-wah filter, through which the guitar signal is sent to be mixed with the original.
To work in real-time, the Wahwactor uses a frame-by-frame algorithm (described by this diagram). The voice signal is sampled at 44100 Hz and analyzed using a 2100 sample Hamming window and a 2048 point Fast Fourier Transform. The guitar signal is sampled at 44100 Hz and filtered using 2100 sample length buffers. The algorithm uses a 1050 sample hop size so that we have a 50% overlap in synthesis. This overlap is necessary to smooth the filter phase frame to frame variations.
Apart from the wah-wah, other effects have been implemented including filter based effects such as phaser or flanger, and envelope based effects such as tremolo. None of them has proven to be as intuitive or show a relevant phonetic-sound linkage as in the wah-wah.
Wahwactor v0.1 is available as a VST effect plug-in for Windows and it is free, although feedback will be appreciated.