Physical Outputs

Physical variables (force, pressure, velocity, ...) are obtained by summing traveling-wave components, as shown in Fig. 1.11.

Figure: Extracting a physical signal from a digital waveguide using delay-line taps (defined in §1.5).

It is important to understand that the two traveling waves in a digital waveguide are now components of a more general acoustic vibration. The physical wave vibration is obtained by summing the left- and right-going traveling waves. A traveling wave by itself in one of the delay lines is no longer regarded as ``physical'' unless the signal in the opposite-going delay line is zero. Traveling waves are efficient for simulation, but they are not easily measured directly in the physical world [453], except when the traveling-wave component in one direction can be arranged to be zero [401].

For a full derivation of digital waveguide theory starting with the basic wave equation for ideal strings, see Appendix G.