Background (Updated October 2021)
Since version 4 Nyquist plug-ins, the global variable that passes the track audio from Audacity to Nyquist changed from S to *TRACK*.
For process and analyze plug-ins, audio is passed from audio tracks to Audacity as the value of *TRACK*.
*TRACK* is a global variable.
For mono tracks the value of *TRACK* is a sound object.
For stereo tracks the value of *TRACK* is an array with two elements. Each element is a sound object.
The first element of *TRACK* may be accessed with (aref *track* 0) and this is the sound from the left channel.
The second element, (aref *track* 1) is the right channel.
To return a stereo track to audacity, an array with two elements, where each element is a sound needs to be returned.
; create an array with noise as the first
; element and a 100 Hz tone as the second