Karplus-Strong synthesis

The Evolver manual has a brief and cryptic note about “Karplus-Strong synthesis” in the manual.

Karplus-Strong synthesis (named for its 2 “inventors”) is a method used to simulate plucked strings involving a simple feedback loop with a lowpass filter.

The Karplus-Strong model is functionally the same thing as the Resonator model we just made, with one key difference. In Karplus-Strong synthesis, we only want to hear the sound of the delay feeding back on itself. The sound that feeds (or “excites”) the delay is unimportant.

There are 2 ways to implement it using Evolver, each providing different timbres. One uses the digital delay, the other uses the feedback channels.

In both cases, you need to use MIDI note number to modulate either the delay time (if using the digital delay) or the feedback pitch (if using the feedback channels). As we have noted in a few exercises, this requires the use of 2 modulation slots to enable keyboard tracking of pitches.

Let’s start with the MIDI-tracking feedback resonator we made earlier:

• OSC 1, 2, 3, 4 level = 0

• Feedback Level = 60

• Modulation Slot 1 Source = MIDI note number

• Modulation Slot 1 Destination = Feedback Frequency

• Modulation Slot 1 Amount = +99

• Modulation Slot 2 Source = MIDI note number

• Modulation Slot 2 Destination = Feedback Frequency

• Modulation Slot 2 Amount = +99

We’ve cranked feedback up, and have set things up so that MIDI notes determine the delay line’s pitch.

Now all we need is an “impulse” to get the delay going.

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Дата добавления: 2015-08-20