Owner`s manual

40
CHAPTER 4 -
Modular Components of the TimewARP 2600
CHAPTER 4 -
4.9
Ring Modulator
The
Ring Modulator
is essentially a multiplier; from its two inputs A and B it produces the
Ring Modulator is essentially a multiplier; from its two inputs A and B it produces the Ring Modulator
output function A x B / 5. The kind of transformation this effects on input signals depends
to a large extent on what they are and on whether the modulator is AC or DC coupled to
them. This is selected by the
Audio/DC
switch at the bottom of the modulator.
Audio/DC switch at the bottom of the modulator.Audio/DC
When the inputs are AC coupled (
Audio
When the inputs are AC coupled (Audio When the inputs are AC coupled (
position of the switch), any DC component
present in them is canceled before they are fed to the modulator. Thus a sawtooth that
starts from zero and goes to+l0vV will instead start at -5vV and move to +5vV so that
its overall positive and negative deviation cancels to zero. Under these conditions the
modulator will generate from any two periodic signals an output signal consisting of the
sum and difference frequencies that can be generated from the frequencies of the two
inputs. The input frequencies themselves will be suppressed.
If both signals are audio-frequency, a large variety of harmonic and inharmonic timbres
can be produced from the modulator, depending on the ratio of the input frequencies
and on their own harmonic content. If A is a sine wave and we represent its frequency by
Fa, and B is a complex waveform of frequency Fb with overtones 2Fb, 3Fb, 4Fb, etc., then
the output of the modulator will be a complex waveform with frequency components
Fb + Fa, Fb - Fa, 2Fb±Fa, 3Fb ± Fa, 4Fb ± Fa, etc. A moment’s experimentation with the
prewired sawtooth and sine inputs to the modulator will demonstrate the complexity of
the timbres that can be generated by this simple means.
If, still with AC coupling, one input is subsonic and the other at some audio frequency,
there will be an output from the modulator only when the value of the subsonic input
is changing, and the output will be roughly proportional to the rate of change. If, for
example, the subsonic input is a square wave, the modulator output will be a series of
short, decaying tonebursts – one at each rise or fall in the input signal.
When the inputs are DC coupled, any DC component in either one of the inputs will
pass into the modulator and affect the modulating process. The effect when both
inputs are at audio frequency is to allow into the output waveform some of the input
frequencies in addition to the sum and difference frequencies. The effect when one of
the inputs is subsonic is that the modulator operates as a voltage-controlled ampli er:
the output amplitude will be in direct proportion to the instantaneous amplitude of the
low-frequency input and will vary as its absolute value varies. Also, the output phase will
reverse when the low-frequency input signal changes from positive to negative or vice
versa.
The AC-coupling time constants are 235 msec, for the left input and 90 msec, for the right
input.