You can think of a vocoder as a morphing multiband equalizer, in which the morphing is controlled by a spectral analyzer. Typically, speech (called the modulator) is analyzed and matching equalization is applied to a pitched, harmonically rich source (called the carrier). Lightning-fast personal computers have allowed the quality of analysis and the number of bands to increase radically, and the uses for vocoding have expanded accordingly. In this column, I'll discuss an unusual approach to vocoding that has broad application: using the same signal as modulator and carrier.
FIG. 1: This is the simplest routing for using the output of Dr:rex as both the modulator and carrier for the BV512 vocoder.
Using the same signal as modulator and carrier may seem pointless, but it can be very effective used with other signal processing, either inside the vocoder or applied prevocoder to the carrier or modulator. I'll use Propellerhead Reason's BV512 vocoder for my examples, but any high-end vocoder can produce similar results.
The BV512 gives you four ways to manipulate the relationship between the analyzer and the equalizer frequency bands: you can shift all equalizer bands up or down, emphasize the high- or the low-frequency bands, boost or attenuate individual bands, or completely remap the band dependencies (that is, change which analysis band controls which equalizer band). In each case, the frequencies that are prominent in the modulator control different frequency bands of the equalizer.
In addition to the BV512 vocoder, you'll need a sound source; for my examples, I've used Reason's Dr:rex. Use a Spider Audio module to route the stereo output of Dr:rex to the carrier inputs of the BV512 as well as to one of the Spider's merge channels. Then route the output of the merge channel to the modulator input of the BV512, which is mono (see Fig. 1).
Load a harmonically interesting loop into Dr:rex, press the Preview button, and use the BV512's Dry/Wet knob to hear the difference between the raw loop (dry) and the vocoded loop (wet). With the default BV512 settings, the wet version will sound a little pinched, with the highs and lows rolled off a bit. Turning the Decay knob all the way up and the HF Emph knob to about 7 will produce the closest match, but the BV512's presence will always make itself known.
Start by manually adjusting some of the BV512 frequency band levels. Switch between Equalizer and Vocoder modes to hear the difference between fixed and dynamic equalization. Also experiment with the number of bands; more is not always better. I find 16 and 32 bands to be the most usable in this context, but even 4 and 8 bands produce interesting results.
Next, experiment with the other BV512 controls. The Shift control has the greatest impact, and you can automate it by cabling Dr:rex's LFO output to the BV512's Shift input. That produces an effect reminiscent of phasing or flanging (see Web Clip 1). Now flip to the back of the rack, disconnect the Shift automation, and draw some cables between different outputs and inputs in the Individual Band Levels section. You can use a Spider CV module to connect one output to several inputs, as well as to combine several outputs.
Betwixt and Between
Effects inserted in either the modulator or the carrier signal path often have a subtler impact than usual. Delay lines work especially well, and you can use high feedback in the modulator path. (Ensure that the delay is panned fully to the side that feeds the modulator's mono input.) Try a 16th-note delay in the modulator path, with a 10 to 50 ms delay in the carrier path. Try a delay of a few 16th notes in the modulator path, with a longer delay in the carrier path (see Web Clip 2). Modulator delay will have more impact with short BV512 decay settings.
The distortion and destruction effect Scream also works well in the modulator path. If you put Scream inside of a Combinator, you can automate its Damage and Body Type selectors by assigning them to Combinator rotaries and automating those. That works particularly well with percussion loops (see Web Clip 3). Web Clip 4 is a Reason song that contains all the examples in this article.
Len Sasso is an associate editor of EM. Visit his Web site atwww.swiftkick.com.