Chatter: Craig Anderton - "Drumcoding" Guitar

September 5, 2013

A PREVIOUS COLUMN COVERED how to use drums with a noise gate to “gate” a guitar part, thus giving a super-rhythmic sound where you hear the guitar only when there’s a drum hit. Another way to interact with drums is with a vocoder, which most people use to create “talking guitar” effects. Unlike gating, which only affects level, vocoders split your voice into different frequency bands; signals in these bands trigger corresponding frequency bands for the guitar, so the guitar has the same frequency spectrum characteristics as your voice. But if you use drums instead of a mic, then the drums trigger these different frequencies, resulting in a complex, rhythmic, synched sound. Several programs have built-in vocoders; we’ll look at Ableton Live’s implementation, as well as Reason’s, for this application.


A vocoder has two filter banks and two inputs. The carrier input is the sound you want to modify (like guitar), and the modulator input provides the signal that does the modifying— in this case, drums. The modulator’s filter bank divides the signal into different frequency bands, generates
Fig. 1—Live’s Vocoder is inserted in the Drums track (which serves as the modulator), and processes the signal coming from the Guitar track.
a control signal from each band, and then uses these control signals to change the levels of corresponding bands in the carrier’s filter bank. For example, when a kick drum hits, the modulator’s bank will detect low frequencies and let through the corresponding low frequencies in the carrier’s filter bank. If it’s a cymbal hit, it will let through the corresponding high frequencies. This is how vocoders can “impress” speech on an instrument when a mic provides the modulation signal. The modulator’s filters identify the “ahh,” “eee,” “ooo,” and other frequencies, and open up corresponding filters in the carrier’s filter bank.


With Live, choosing the modulation input simply involves inserting the vocoder into the track providing the modulation signal (Fig. 1). For the carrier, you can select options within the vocoder, such as noise, selfmodulation, and pitch tracking. But we want an external signal—in this case, the one from the guitar track.

After selecting External as the carrier, an Audio From field becomes available. You can then select a track (like the guitar track), a send return, or the master. You can also choose whether the audio from this external source is pre- or post-effects.

Fig. 2—Patching into Reason’s BV512 Vocoder. The Vocoder is an insert effect in the Guitar track, while the Drums track provides the modulation input.
Figure 2
shows the patching needed to use Reason’s vocoder with a Drums and Guitar track. Follow the patch cords. The Drums track feeds the modulation input, while the vocoder gets its carrier from the Guitar track, then feeds the vocoded output back into the Guitar track.


All vocoders have additional controls to modify the sound further. With Live, Dry/Wet adjusts the ratio of the dry modulation sound to the vocoded sound. Formant sets an overall timbre, while Depth determines how much modulation occurs. Other controls include a Gate, where only modulation signals above a certain level have any effect; a selector for the number of bands in the filter banks (fewer bands give a less defined sound); and Level sliders for each band, which act like a graphic equalizer. Reason’s vocoder has a similar complement of controls, but also has a Hold control that “freezes” the vocoded sound when clicked.

The real fun with vocoders begins when you start playing around with these controls. Anything can happen, and often does!

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