Waveguide filtering

The input source signal for the delay line and the type of modification applied by the waveguide chain play a key role in determining the characteristics of the instrument. Waves 

Waveguide synthesis is largely compatible with most available sound synthesis programing languages standard unit generators can often be used as the building blocks for waveguide networks. 

More sophisticated waveguide examples implemented in Nyquist are available on the CD-ROM in the folder nyquist use a Web browser to open the file example-home.htm for explanations. 

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Boriskina, S.V., Berrsorr, T.M., SeweU, P., Nosich, A.I., 2003, Tuning of elliptic whispering-gallery-mode microdisk waveguide filters, J. Lightwave Technol. 21(9) 1987-1995. 

Stockermans, R. J., and Rochon, P. L. Narrow-band resonant grating waveguide filters con-strueted with azobenzene polymers. Appl. Opt. 1999, 38, pp. 3714-3719. 

This chapter will focus on one-dimensional physical models, and on the techniques known as waveguide filters for constracting very simple models that yield expressive soimd synthesis. First weTl look at the simple ideal string, and then refine the model to make it more reahstic and flexible. At the end we will have developed models that are capable of simnlating an interesting variety of one-dimensional vibrating objects, inclnding stiff stmctures such as bars and beams. 

The two delay lines taken together are called a waveguide filter. The sum of the contents of the two delay lines is the displacement of the string, and the difference of the contents of the two delay lines is the velocity of the string (check this yourself using the methods and equations given in Appendix B). If we wish to pluck the string, we simply need to load one-half... 

Amersfoort, M. R., Soole, J. B. D., LeBlanc, H. R, Andreadakis, N. C., Rajhei, A., and Caneau, C. (1996). Passband broadening of integrated arrayed waveguide filters using multimode interference couplers, Electron. Lett. 32, 449-451. 

The implementation of a source model is not straightforward. However, once the model is implemented, it is not complicated to interpret the role of their synthesis parameters. Take, for example, a singing voice-like instrument. A loose model using FM, for instance, would provide relatively complex synthesis parameters, such as modulation index and frequency ratio. Conversely, a source model using waveguide filtering, for instance, would provide more easily interpreted synthesis parameters, such as air pressure, vocal tract shape and throat radiation output. 

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