GDAM: scratching

Scratching in GDAM is based on the Bender plugin - an inline filter which keeps a large buffer of audio and allows playback at any speed, backward or forward, from any point in the buffer. If you are familiar with the Buffer Override VST filter, I am told it uses this technique.

Bender plugin can manage the input to the buffer in various ways; it can keep the input at full speed, advance only when needed, or even drop bars of music to keep playing in beat, without making progress through the song.

Scratching in GDAM allows the user to set certain cuepoints in the audio stream, and jump to them, while playing backward or forward at any pitch. The ability to teleport between point in the audio stream breaks a major limitation of vinyl scratching: to get from one part of a sample to another, the vinyl DJ has to move the needle along the groove. To get there fast, the record spins fast and the sample plays at a higher pitch. The scratch DJ may selectively mute parts of the scratch to obscure some of the "incidental" pitch, but there is noneless a very rigid relationship between where in the sample you can be, how fast you are moving through the sample and what the pitch is at any moment.

GDAM's ability to jump to marks within the sample allows different parts of a sample to be played back-to-back in a way that is impossible in vinyls. On top of Bender, it is even possible to switch seamlessly into timestretching and pitch shifting, breaking the speed/pitch relationship. In theory a bit like going from pushing a car on a flat track to flying uninhibited through 3d space.

Another technique is to take timestretching to the extreme that position does not progress forward or backward on its own. It plays a microloop of the current position, and you can drag the playhead back and forth while changing the pitch independently. You can do a record stall in place by fading pitch down to 0, scratch back and forth at any consistent pitch, and all kinds of other tricks impossible with vinyl.

For MIDI control for scratching I like to use the pitchbend wheel - pulling it towards me to rewing and pushing it away from me to play > 100% speed. A nice thing about the pitch bend wheel is that it returns to its detente position when you remove your hand, in the same way that a record returns to full turntable speed when you remove your hand from it.

So of course pitchbend 0 always mapped to 100% speed. But I have a number of different mappings for the rest of pitchbend range. The two most common are 1) pulling back from detent slows from 100% to stalled then increases to -200% or -400% at pitchwheel full back 2) pulling back from detente instantly trigger 0% and from there increases to -400%. 1) gives a snappier scratch, 2) is useful if you want to stall a record but GDAM also offers plugins which do this perfectly so it didn't get as much use.

Although I've often dropped a bit of scratching into sets and demos, I never really spent time developing routines and pushing the limits of what is possible.