Plucking and Striking

In Chapter 4 we talked some about how the point of excitation of a plucked string determines which harmonics are present, and how strongly, in the spectrum. We also talked about this in Chapter 12 for square membranes. In these cases of systems with simple geometry, we can predict what the modes of the system should be, and then use Fourier methods to compute the amplitude of each of the modes. 

Hgnie 14.4. Strikes on a wooden bar with a hard stick (left) and soft mallet (right). 

We could continue plucking and banging on all kinds of objects, with all sorts of striking and plucking devices, for many more pages. Indeed, I encourage you to do so in your own experiments. For now we ll skip plates and 

To conclude our discussion of plucking and striking, two models of impulsive excitation will be introduced. The first model is simple, and fits well within our signal-processing framework of source/filter residual extraction. In general, we know we can inject the residual back into a filter designed using LPC or 

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Dennis s rap drew on the theory of sound. If you pluck a string, it will sound in the octave in which it is struck, but it will also sound in octaves above and below its key. It has what are called harmonic overtones. If you strike the chord and then squelch it, you can still hear the harmonic overtones, a phenomenon that had fascinated Pythagoras. Dennis pointed out to us that one can use two sounds to cancel each other if the two sounds are exactly the same in relation to each other. 

A wide variety of sounds can be synthesized using modal synthesis. Any object which exhibits a few modes and is excited by striking or plucking is a likely candidate for modal modeling. Such objects might include metal pots and pans, glasses, etc. Modal synthesis can also work well for simple wooden objects such as blocks, boards, etc. 

Track 14] Direct and Discrete Mass/Spring/Damper Oscillations. [Track 15] Guitar Pluck Edge versus Center, Playing Overtones. [Track 16] Coffee Mug Strike and Residual. 

Chapter 14 deals with plucking, striking, bowing, and rubbing excitations for physical models. Friction is discussed at length. MIDI and other protocols for controlling physical models are discussed. Finally, some custom-built physical modeling synthesis controllers are shown. 

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