More additive synthesis

The major triad (page ) is one example showing how to combine several sinusoids together by summing. Here we will show two more examples. Patch A07.fusion.pd (Figure 1.13) shows four oscillators, whose frequencies are tuned in the ratio 1:2:3:4, with relative amplitudes 1, 0.1, 0.2, and 0.5. The amplitudes are set by multiplying the outputs of the oscillators (the *~ objects below the oscillators).

Tthe second, third, and fourth oscillator are turned on and off using a toggle switch. This is a graphical control, like the number box introduced earlier. The toggle switch puts out values of 1 and 0 alternately when clicked on with the mouse. This value is multiplied by the sum of the second, third, and fourth oscillators, effectively turning them on and off.

Even when all four oscillators are combined (with the toggle switch in the ``1" position), the result fuses into a single tone, heard at the pitch of the leftmost oscillator. In effect this patch sums a four-term Fourier series to generate a complex, periodic waveform.

Figure 1.13: Additive synthesis using harmonically tuned oscillators.

Patch A08.beating.pd (Figure 1.14) shows another possiblity, in which six oscillators are tuned into three pairs of neighbors, for instalnce 330 and 330.2 Hertz. These paris slip into and out of phase with each other, so that the ampltude of the sum changes over time. This is called beating.

Figure 1.14: Additive synthesis: six oscillators arranged into three beating pairs.

Oscillators may be combined in other ways besides simply summing their output, and a wide range of resulting sounds is available. Patch A09.frequency.mod.pd (not shown here) demonstrates Frequency Modulation synthesis, in which one oscillator controls another's frequency. This will be more fully described in chapter 5.