084 SECTION ELEVEN: PREAMP, ENVELOPE FOLLOWER, RING MODULATOR

Perhaps the most important thing to learn about distortion is not so much if it is a good thing or a bad thing, but rather when it is appropriate and when it is not. For instance, if one is trying to make a recording of Beethoven’s fifth symphony, distortion is probably a bad thing. If one is trying to create hard-core or industrial music, distortion is probably a good thing. The presence or absence of distortion is often times determined by the genre of music being produced.

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The preamplifier is generally used when interfacing the ARP 2600 with other equipment. Specifically, the preamp is used to bring the output levels of other devices up to the level required by the 2600. This opens the door to hundreds of new possibilities, far too numerous to list here. A few possibilities include: connecting a microphone for adding distortion, filtering with the VCF, or shaping with the VCA. One could also connect other synthesizers to make use of the ARP’s filter and/or VCA. One could feed the ARP’s own signals (either control or audio) into the preamp for amplification and/or distortion. Audio from a CD player could be input for distortion or filtering (this works particularly well with drum loops!) While these are just a few ideas, the important thing to understand is that most external equipment can be connected to the ARP using the preamplifier.

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Nothing is normalled to the preamplifier’s input, but the preamp’s output is nor- malled to something: the input of the envelope follower. The envelope follower is located on the left most position on the cabinet. Like the preamp, the envelope fol- lower performs a fairly straightforward job. Looking at the module (Figure 11-6) one can see that it has a single input, an output, and a single fader.

The envelope follower turns incoming audio-range waveforms into a steady control voltage up to +10 volts which can then be sent to other modules. For instance, if one connected a sawtooth waveform from an oscillator, the envelope follower analyzes the amplitude of the incoming waveform. In Figure 11-6, the saw wave coming into the envelope follower’s input is shown in red, while the output is shown in purple. The amplitude of the incoming waveform can be attenuated using the single fader on the envelope follower.

The envelope follower is used to create an envelope which matches the volume envelope of the incoming waveform. Thus, one must already have changes in amplitude if one wants to make effective use of the envelope follower. Most of the time, it is used with external devices, hence the fact that the preamp’s output is normalled to its input. One way the envelope follower is commonly used is to track the amplitude of a signal coming into a microphone. As

Figure 11-6: The envelope follower Figure 11-7: The output of the envelope follower

a person speaks more loudly into the microphone, the more control voltage exits the envelope follower. It is important to remember that the envelope follower is not able to sense changes in frequency, and thus, changes in pitch will have no effect on the signal it puts out. It will only detect and react to the volume of the incoming signal. The envelope follower can be used in place of an EG whenever an external signal is available for use. The envelope follower can thus be used to modulate the VCO’s, VCF, or VCA in a fashion very similar to the way the EG’s modulate them. CD track 60

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The ring modulator is the most complex of the three modules presented in this section. Many modern synthesizers claim to have a ring modulator when they actually have a balanced modulator. The difference between the two is actually in the design and construction of the circuit. This point is beyond the scope of this book, but it is important to understand that they are really two different modules. Many synthesizers today have modules which produce ring modulator-like effects and claim to have ring modulators, when the truth is that these modules are not ring modulators at all. Synthesizer companies real- ize that musicians will be more comfortable working with something which is familiar, and thus continue to use the term “ring modulator.”

The ARP 2600’s manual gives a succinct, but mostly useless definition of the way the ring modulator works: “The ring modulator is essentially a voltage multiplier; from two inputs A and B it produces the output function A x B/5.” The ring modulator is much easier to understand when the kind of modulation it allows is understood. The ring modulator allows a new kind of modulation which has not been experienced up to this point. Amplitude Modulation or

AM is a process in which the amplitude of one waveform is used to modulate

the amplitude of a second waveform.

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Essentially, many new harmonics are added to a sound, and the original sound is then removed from the signal using cancellation. To accomplish this, two different signals are input to the ring modulator’s inputs which can be seen in

Figure 11-8. Each incoming waveform has its own frequency content. (Frequency content is defined as all of the harmonics of a particular waveform. This is also sometimes referred to as harmonic content.) The ring modulator adds the entire harmonic content of the two waveforms, and subtracts the harmonic content of the two waves. The ring modulator comes up with a sum and a difference of these two incoming waves. For instance, a 210 Hz fundamental would be added to a 441 Hz fundamental to give a 651 Hz fundamental. Similarly, an 255 Hz fundamental could be subtracted from an 880 Hz harmonic to give a 625 Hz harmonic. The ring modulator causes every harmonic of one incoming waveform (including the fundamental) to be added to every harmonic (including the fundamental) of the second incoming waveform and every harmonic of one incoming waveform to be subtracted from every har- monic of the second incoming waveform. The results are difficult to predict.

Figure 11-8: The ring modulator