Sound Design Workshop: Klangumwandler Redux

MULTIBAND FREQUENCY SHIFTING WITH VIRSYN PRISM
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Frequency shifting, which linearly shifts the entire frequency spectrum of a sound, has long been used for turning pitched sounds into inharmonic, bell-like timbres. These sounds, often produced by the Bode Frequency Shifter (designed by Harold Bode and marketed by Moog Music), feature prominently in early electronic music.

Pitch-shifting, which is more common and usually involves granular or FFT processing, preserves timbre by exponentially shifting the spectrum — in effect, stretching the spectrum as it is shifted so that the ratios between the spectral elements are preserved. For instance, if you start with two sine waves an octave apart (say, 220 and 440 Hz) and frequency shift them by 110 Hz, their ratio (330 to 550 Hz) is no longer 1:2 (an octave). On the other hand, if you pitch-shift them by 50 percent, they remain an octave apart (330 and 660 Hz).

Color Separation

VirSyn Prism (Mac/Win, virsyn.com) takes a novel, multiband approach to frequency shifting, first breaking the signal into 27 frequency bands and then letting you frequency shift each band independently. The results don't measure up to high-quality pitch-shifting, but that's not the point — you can create effects with Prism that you can't create with anything else. I'll give three examples, using Prism to add color to electric piano, drum, and bass clips without mangling their timbre beyond recognition.

The frequency spectrum area at the top right of Prism's control panel has three tabs: Level, Shift, and LFO. The Level tab works like a graphic equalizer, and that's a good place to start with an electric piano sound. To add some bite, raise the bands between 1 and 5 kHz by around 9 dB and lower the bands below 350 kHz by about 3 dB. That may be a little extreme with a full-wet mix, but it's fine at about 50 percent, which works better for the frequency shifting and LFO in this case.

On the Shift tab, set all bands to maximum. That produces a phased pitch-shifting effect when you manipulate the F-Shift knob with a 50 percent mix and the Range knob set to 1 Semi (a ±1-semitone range). On the LFO tab, set the lowest band around 4 Hz and click on the Flat button, and all bands will be set to the same frequency. LFO knob settings of around 25 percent with a slight F-Shift produce a nice phasing-vibrato effect (see Web Clip 1).

Although Prism doesn't have a built-in MIDI Learn capability, many hosts let you map MIDI continuous controllers to the parameters that the plug-in presents to the host for automation. With Prism you can access all the front-panel knobs, and for the electric piano settings just described, I map the MIDI Mod Wheel to the LFO knob and the MIDI Pitch Bend controller to F-Shift.

Drum and Bass

Prism is a great tool for retuning one drum in a mixed drum track. For instance, when the kick drum doesn't sit well with the bass or another track, use Prism to shift the bottom two or three bands. At the same time, you can use the Level tab to EQ the drums. For kick drum pitch-shifting, set the affected bands to maximum shift and use a full-wet mix, then use the F-Shift knob to dial in the desired kick drum pitch (see Web Clip 2). For tom tracks, try using the Envelope and Release knobs to add a level-tracking pitch-bend.

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FIG. 1: This acoustic bass setup shifts bands 750 through 1,100 Hz down by varying amounts within a 7-semitone range.

With acoustic bass, I like to boost the bands between 750 and 1,100 Hz and then shift them down by varying amounts within a 7-semitone range (see Fig. 1). That affects the bass harmonics without altering the fundamental pitch. I map the MIDI Mod Wheel to the Dry/Wet knob and map the Pitch Bend controller to the Envelope knob. Mixes that are between 25 and 50 percent, together with small, positive envelope settings, produce a subtle scat-singing effect over the bass line (see Web Clips 3 and 4).

Although these examples have emphasized coloration rather than mutilation, Prism can easily mangle your sounds beyond recognition. It's a great tool for creating sound effects, adding texture and motion to pads and ambient tracks, and processing speech. For instance, try processing a speech clip with the lower and upper bands shifted in opposite directions (see Web Clip 5).

Len Sasso is an associate editor of EM. For an earful, visit his Web site atswiftkick.com.

ONLINE LINKS

Frequency shifter or klangumwandler as defined by the Audio Engineering Society (AES)
www.aes.org/e-lib/browse.cfm?elib=155

Sound Design Workshop from the Feb. 2005 issue of EM on frequency shifting drums using the frequency shifter in the Arturia Moog Modular V
emusician.com/mag/emusic_frequency_shifting_tips/