Vocoding is a fantastic effect, used in many genres of music over the past 50 years. Popularised in the seventies, it uses the voice as a way to filter the sound of an instrument. By modulating an instrument with a human voice, you can get complex, robotic and ethereal sounds which are otherwise extremely complex to program into a synth. Here is a list of tricks for using vocoders, both as they were originally intended and some cool alternative uses to make the most out of your music.
Vocoders work by having a carrier signal, which is modulated by a modulator signal. The carrier, typically a synth has a full spectrum of sound, often over most octaves. By modulating it with a voice, the frequencies expressed will match the frequencies of your voice.
Imagine looking into the spectrum analysis of your voice as you speak, you will see peaks at the frequencies being made.
this frequency response of the voice, is applied to the carrier
signal and modulates it as the voice changes.
What if you were to make an EQ curve on the synth that matched the frequencies of the voice, in real time as they are expressed? This is equivalent to what a vocoder does. It follows the vowels of speech and places them on a synth to make the synth talk.
So beyond the traditional use, what can you do with a vocoder? One of my favourites it to add it to the reverbs of an instrument. Create a reverb send, and vocode the reverb tails of the instruments gently. This means there is a nice "following" effect where the reverbs follow the vocals.
This works quite nicely with the reverb tails on a drum kit, though keep the levels controlled as it can be quite overpowering.
A Korg Microkorg XL vocoder synth
You could use your drums as the modulator on a synth, this means the synth will only play when the drums play and only at the frequencies expressed by the drums. This creates a tuned gating effect which can be pulled off successfully with both the correct drums and the correct synth. You will want a synth that can cover the whole frequency range nicely (though high pass it so the sub frequencies don't blast through).
If you have a hard bass line, try pitching the vocals/vocal sample down to the octave of the bass notes and using it to express the note. This works well for dubstep, and drum and bass productions. Remember, to pitch the vocals to the frequency range though as only the upper harmonics of the bass will be let through otherwise.
Skrillex has been known to do this alongside other acts, combining strange gritty sounds and modulating his bass with them to create harder more aggressive basses.
If you have a voice and the main synth playing the melody, you could duplicate the synth and vocode the duplicate track, turning it all the way down and mixing it back up to taste. You will keep the essence of the main, unmodulated synth while adding a bit more complexity that follows both the synth and the vocals.
A great technique is to make the voice "morph" into the synth. Have a vocal track and a synth track in one bus and duplicate, vocoding the duplicate bus, leaving the original untouched. Cross-fade between busses for the vocals to gain a morphing effect into the synth and have them combine nicely.
If you modulate this cross-fade, you can have the vocals dip in and out of the robotic sound as desired. This again is a very obvious effect but it works very smoothly and can sound like very complex vocal processing if done right.
Remember the volumes add up, so use careful limiting on your carriers and modulators so you don't overdo the volume when the peaks line up.