Making Music
  Computer Music Software and Hardware

Carry on singing

Note that it's the voice characteristics that are imposed upon the carrier, not the voice pitch, so to make your voice 'sing' you talk into the vocoder and generate the required notes by changing the pitch of the carrier, perhaps by playing a keyboard. With software vocoders you'll probably prerecord the pitches you need for the carrier and then apply the vocal modulator to this.

The best carriers are those that are harmonically rich so pads, strings and brass are good starting points. The carrier should contain frequencies that are present in the vocal range being used. Our full vocal range runs from around 80Hz to 1kHz although the range used in normal speech will be much less. The frequency range will also be different for men, women and children. Note also that both sources are usually required in order to produce an output. If you stop talking or stop playing, the vocoder output will stop, too.

Computer power has meant that software vocoders don't have to follow the format of their hardware forefathers and many have far more controls. These may include an adjustable number of frequency bands (the more bands, the higher the definition of the audio), bandwidth (narrow bands will produce a thinner sound), filter and resonance controls, envelope settings (which determine how quickly the modulator triggers the carrier) and more.

The trouble with fricatives

Fricatives are high-pitched noise-like sounds such as S, T, K, F and P produced by the mouth rather than the vocal tract, and they often don't reproduce well on a vocoder. Some devices, therefore, add noise to duplicate the sound while others use a low pass filter to remove problem frequencies from the modulator.

If your particular vocoder isn't playing ball, try compressing the vocal on the way into it or compress the audio track.

Pitch and carry

The range of effects you can create with a vocoder is vast. Although naturally associated with voice effects, vocoders can be used with all sorts of sounds and, indeed, they can create many unique sounds suitable for a wide range of music.  Here are a few ways of using a vocoder with mainly non-vocal sounds.

Drums are a firm favourite for vocoder processing. Run a drum loop through a vocoder using a pad for the carrier. Adjust the balance between the original signal and the modulated signal to determine how much of a processed sound you get. Adjust the filter settings so it lets through more high frequencies to accentuate the hi hats and mix these in with the original sound.

Try turning this around - use a drum loop as the carrier and your voice as the modulator. Try speaking individual words and phrases and then take a deep breath and roll out a whole load of words in one breath. Interesting...

We've said the carrier should match the modulator for frequency content and although most vocoders rely on a handful of tried and tested waveforms, it's worth experimenting with other carrier sounds such as wind, surf, rushing water, crowd noises and so on. Run a drum loop through this to produce a 'natural' drum sound.

Try reversing modulator and carrier signals. Knowing how vocoders work, you'll realise that a static modulator (such as a pad sound) will probably not produce interesting results. Dynamic natural sounds, on the other hand, may produce some interesting and musical surprises.

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