Open either a new or existing Logic session file in which you wish to create a vocoder track. Choose a modulator for your vocoder. This will function as the voice of the synthesizer. Create a new vocal track or select an existing vocal track for this purpose. Create one new software instrument and set the track input to Logic Pro 8's included vocoder synthesizer, the EVOC PS 20.
Mute or assign your vocal track to no output if you wish for it to be heard only through the synthesizer; otherwise balance as desired. Open the EVOC 20 PS vocoder synthesizer and in the top-right corner, set the side chain of the synthesizer to your vocal track. Ensure the input on the synthesizer is set to "VOC." Your vocal track now modulates the synthesizer. Play the new track and set the sensitivity setting on the synthesizer so that it captures the vocal track fully. Use the U/V slider to control the mix of synthesized and natural sounds. Consider selecting a preset sound of the synthesizer to begin.
Record a MIDI performance on your vocoder track by ensuring it is record-enabled and then proceed to record as usual. This will save your performance and allow for editing. Play back the session, and you'll hear the synthesized sound modulated by the vocal track.
During playback, set the synthesizer to the desired sound by moving the knobs and sliders featured on the EVOC 20 PS. Choose the frequency range of the track by shortening or widening the large blue slider. Lengthen the attack and release times of the synthesizer to soften attacks and sustain of notes or shorten them to produce a sharp, short sound. Shift the sound of the vocal by using the Format Shift and Stretch knobs. You may add distortion with the noise control, and control the low-frequency oscillator by selecting the desired wave form button and setting the frequency. If you are unsure of what a control does, listen carefully during playback and change the settings to your liking.