KDFX Reference
KDFX Algorithm Specifications
10-161
907 Ring Modulator
A configurable ring modulator
PAUs: 1
Ring modulation is a simple effect in which two signals are multiplied together. Typically, an input signal
is modulated with a simple carrier waveform such as a sine wave or a sawtooth. Since the modulation is
symmetric (a*b = b*a), deciding which signal is the carrier and which is the modulation signal is a question
of perspective. A simple, unchanging waveform is generally considered the carrier.
To see how the ring modulator works, we’ll have to go through a little high school math and trigonometry.
If you like, you can skip the how’s and why’s and go straight to the discussion of controlling the
algorithm. Let’s look at the simple case of two equal amplitude sine waves modulating each other. Real
signals will be more complex, but they will be much more difficult to analyse. The two sine waves
generally will be oscillating at different frequencies. A sine wave signal at any time t having a frequency f
is represented as sin(ft + φ) where φ is constant phase angle to correct for the sine wave not being 0 at t = 0.
The sine wave could also be represented with a cosine function which is a sine function with a 90° phase
shift. To simply matters, we will write A = f
1
t + φ
1
for one of the sine waves and B = f
2
t + φ
2
for the other
sine wave. The ring modulator multiplies the two signals to produce sin A sin B. We can try to find a
trigometric identity for this, or we can just look up in a trigonometry book:
2 sin A sin B = cos(A - B) - cos(A + B).
This equation tells us that multiplying two sine waves produces two new sine waves (or cosine waves) at
the sum and difference of the original frequencies. The following figure shows the output frequencies
(solid lines) for a given input signal pair (dashed lines):
Figure 10-74 Result of Modulating Two Sine Waves A and B
This algorithm has two operating modes which is set with the Mod Mode parameter. In “L*R” mode, you
supply the modulation and carrier signals as two mono signals on the left and right inputs. The output in
“L*R” mode is also mono and you may use the L*R Pan parameter to pan the output. The oscillator
Frequency
Magnitude
A B A+BB-A
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