As yet there are no official instructions for the Easy Vocoder effect (the author Edgar Franke has it on his “To Do” list).
Here’s some information that the author posted on the forum:
The “Easy Vocoder” needs no special stereo audio tracks with “carrier” and “modulator” channels, it can be applied to an ordinary Audacity mono or stereo audio track like any other Audacity effect. The “Easy Vocoder” works best if applied to voice recordings, but also works with any other audio tracks.
Technical details: Instead of using “carrier” and “modulator” channels of an Audacity stereo audio track the “Easy Vocoder” uses built-in “sinewave” &optional “noise” and “pulse” carriers for each vocoder band and then adds the amplitude-modulated carriers together to produce the vocoder sound.
Advantage: No “split stereo track” / “make stereo track” fiddling any more like with the original Audacity “Vocoder” effect.
Disadvantage: The “Easy Vocoder” cannot modulate a “voice” onto a music track, it can only make a voice recording sound like an alienatic robot.
and
I agree, the “Vocoder” is a fundamentally different effect than the “Easy Vocoder”, even if both names sound very similar.
The main internal difference and the main reason why combining both effects is not as easy as it sounds is that the “Vocoder” uses one single carrier for all vocoder bands, while the “Easy Vocoder” uses many different carriers with different frequencies, i.e. one carrier per vocoder band.
The “Vocoder” uses one single carrier for all vocoder bands. The carrier as well as the modulator are spitted into frequency-limited “bands”, then the “carrier” band is modulated by the respective “modulator” band, the resulting signals are bandpass-filtered again to remove the aliasing, and in the end all bands are summed together to produce the vocoder sound.
The “Easy Vocoder” doesn’t use a bandpass-filtered “carrier”, instead it uses one sinewave oscillator per vocoder band. The oscillators are modulated by bandpass-filtered “modulator” bands (produced from the Audacity audio track) with the same mid-frequency as the respective oscillator frequency. The modulated oscillator signals then are bandpass-filtered again to remove the aliasing, and finally summed together to produce the vocoder sound.
You will find the full discussion here: New/improved plug-ins for potential inclusion in Audacity