Ring Modulation

Ring modulation (RM), introduced as the beat note waveform, occurs when modulation is applied directly to the amplitude input of the carrier modulator:

$$x(t) = \cos(2\pi f_\Delta t)\cos(2\pi f_ct).$$

Recall that this multiplication can also be expressed as the sum of sinusoids using the inverse of Euler's formula:

$$x(t) = \frac{1}{2}\cos(2\pi f_1t) + \frac{1}{2}\cos(2\pi f_2t),$$

where $f_1 = f_c-f_\Delta$ and $f_2 = f_c+f_\Delta$.

Figure 2: Spectrum of ring modulation.