The EM Poll

Shifting Timbres

Oct 1, 2006 12:00 PM, By Len Sasso

           

In 1958, songwriter Ross Bagdasarian made history of a sort by recording a vocal and playing it back at double speed in “The Chipmunk Song.” The novelty of radically pitch-shifted vocals has long gone, but pitch-shifting can still produce useful changes of timbre, and in the digital domain, it's a piece of cake.

FIG. 1: Set the Shift and Transpose parameters in Dimension Pro’s Multisample window to equal but opposite values to create pitch-shifted timbres.

Classic, speedup-style pitch-shifting changes the timbre as well as the pitch of natural sounds because the timbres of those sounds are shaped by the physical objects that create them. When a vocalist sings notes an octave apart, the vocal tract, which acts as a filter, doesn't magically halve or double in size. But when you pitch-shift a sung note, you do shift the resonances that characterize the singer's voice, which roughly correlates to changing the size of the vocal tract. The same holds true for acoustic instruments: a note played on a cello sounds different than the same note played on a violin.

Another Dimension

For this article, I'll use the Cakewalk Dimension Pro sample-based synthesizer in my examples. Dimension Pro makes it especially easy to pitch-shift the samples in a multisample map, and then transpose the map to preserve the original MIDI Note Number to pitch relationships. If you don't have a sample player that automatically does that, you can pitch-shift each of the samples in a sample editor or retune them in the sample player, and then remap them manually. But bear in mind that that technique requires classic pitch-shifting, not granular or other methods that preserve timbre.

Start by initializing Dimension Pro, and then load the factory preset Grand Piano 1v 4th. Doing so places a grand-piano multisample in Element 1, leaving the remaining Elements empty. Copy Element 1 to Elements 2, 3, and 4, and set their Shift parameters to 12, 24, and -12, respectively. Play a note, and you'll hear a 4-octave layer with the lowest octave having a dark timbre and the higher 3 octaves getting progressively tinnier.

Now set the Transpose parameters for those same Elements to -12, -24, and 12 (see Fig. 1). That places all four Elements at the same pitch but preserves their differing timbres. Open the VectorMixer and move its cursor around as you play to better hear the individual timbres and to mix them to taste (see Web Clips 1 and 2). The transposed Elements no longer cover the entire keyboard; you'll need to take that into account when using the Elements in other patches. To use them in other patches, you'll need to save each Element to disk.

I've chosen octave shifts for this example to make the effect painfully obvious, but shifts of a few semitones often produce more subtle and usable results. For instance, start with the Full Acoustic (f) bass preset, and try different small shifts to produce a variety of acoustic-bass timbres (see Web Clip 3). On the other hand, large shifts can yield interesting radical results.

More Is More

This technique is useful only with multisamples. If you need convincing, load any single sample you like into an Element and try offsetting Shift and Transpose settings — the sound doesn't change. There's nothing magical about multisamples, but multisamples are needed only when pitch-shifting affects timbre.

A good way to search for useful pitch-shifting candidates is to load Dimension Pro multisamples into individual Elements; the more key zones in the multisample, the better. The Hammond Soul multisample, which samples every note, works well, whereas the fm1 electric-piano preset, which has only two samples per octave, doesn't. That rule is not absolute, though. The Hard Sync multisample has only 13 zones but is great for pitch-shifting (see Web Clip 4).

Pitch-shifting is also useful for unpitched sounds, such as percussion. Load the one-Element preset called Acoustic Kicks and Snares. Copy Element 1 to Element 2, set Element 1's Hi Key parameter to 59, and set Element 2's Lo Key parameter to 60. That places the kicks and snares in separate Elements. Next, set the Element 1 and 2 Shift parameters to 5 and -5, respectively. The kicks will now all be a little thinner, and the snares will be a little darker. With unpitched sounds, you generally don't want to use an offsetting Transpose; instead you want to preserve the key-to-sound relationship.

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