Adding the Initial Bow Scrape
Drawing a bow across a string creates a brief scraping noise that can be heard before the string’s oscillation becomes stable. Our model now has sustained bow noise, but not the initial scraping sound.
Advanced physical models have been developed that produce noisy sounds naturally, and are based on techniques such as modeling the bow’s width, and the torsional twisting of the string under the bow. But they’re too DSP-intensive for our use. We’ll have to settle for something that fits into our patch limit.
So, on this page, we’ll temporarily depart from physical modeling, and synthesize our scrape.
Our technique will be to synchronize two sawtooth oscillators together, and then apply filtered noise to the synchronized oscillator. We’ll shape the output amplitude into a short pulse with an AHD envelope, and apply the result to the model, at the output of the bow/string junction.
Credit for developing this technique goes to Ken Elhardt, who has created some amazing bowed string emulations on the Nord Modular.
The bow scrape in action
Below is a patch that demonstrates this technique. Two oscillators are synchronized together, and both track the keyboard pitch. The pitch of the synchronized oscillator is also modulated by filtered noise, whose amplitude can be varied. The result is shaped into a burst with an AHD envelope.
Since the scrape is created at the point where the bow meets the string, we’ll inject the scrape into the model at the output of the bow driver.
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A side benefit:
Plucking the string
Now that we have a noisy percussive source feeding the string, we can think about plucking it. When we do that, we find that the Friedlander-Keller bow driver gets in the way. But if we can turn off the output of the bow driver, we can use our bow scrape generator to “pluck” the string.
Below is a patch that does this. A switch has been added at the output of the Friedlander-Keller bow driver, which disables the output. Now, the string can be plucked by our bow scrape generator.
When plucking the string, the length of it’s sustain can be controlled by the “Bridge Gain” knob. Also, the “Bow Position” knob controls the pluck point.
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