Fourier Synthesis seen and heard
Read Instructions for this applet, particulary to turn off audio before quitting. The amplitude in the spectrum is given in a "logarithmic" scale of decibels, therefore you cannot directly apply the amplitudes given, say, in Table 4-1 to this scale. (Decibels are explained on page 153.) If you want to recreate the synthesis of Fig 4-6, for example, put the fundamental at 0 db (top of the scale) for A = 1. A = 1/2 for the next harmonic will then be at -3 db, A = 1/3 at -5 db, A = 1/4 at -6 db ... For all the spectra in table 4-1, where the amplitudes decrease as 1/(integer to some power), the amplitudes on the db scale will decrease in a linear fashion.
You can control the phases by clicking on the appropriate bars. As the figures of Chapter 4 show, all the standard waves have components that start in phase (phase 0), except the triangle wave, where alternate components have phase 180 (or -180).