Connect a microphone to one of the audio inputs and set the level switch of the input to "Mic". Different microphones will have different effects on your voice. With vocoders, it is not necessary to use the highest quality microphones or cables, since the voice is so substantially altered. Try experimenting with different microphones.
Navigate to Global Page P0: Basic Setup-Audio. You will make some basic adjustments in this section, which controls the audio routings of the OASYS.
Set the Bus Select to "L/R" for the audio input which you have connected the microphone to. This routes the audio input to the main output of the OASYS, so you can monitor the signal coming from the microphone while you are setting up.
Adjust the "Level" control as high as you can until you can speak into the microphone without your voice distorting. Different microphones and voices will require different level settings.
For whichever audio input you are using with the microphone, set "Bus Select" to the Off position and set the "FX Control Bus Select" to 1. This routes the microphone to an FX bus, which you then can route wherever you like. You will route it to the vocoder.
In the Vocoder effect section, change the "Modulator" source to FX Control Bus 1. This will route the microphone into the Modulator input of the Vocoder. Now your voice will affect whatever synth sound you route into the Carrier input.
Select a synth sound to use as the Carrier input. This will determine the basic timbre quality of the vocoded sound. Good sounds to use are timbrally rich, such as sawtooth or pulse width-modulated waves.
Speak into the microphone and play the keyboard at the same time. Play chords to get the sound of a synthetic choir, and monophonic melodies for a solo electronic voice. Play a single, unchanging note while speaking to create a talking, droning note.