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Modular Synthesizer Effects (Part 2)

Flora & Fauna of the Patch Cord Jungle

(In last issue's installment, Jim started off by giving some opinions about the current state of the synthesizer art, and why the synthesizer - which should be one of the most versatile instruments in existence - is often one of the least versatile. To recover that missing versatility, Jim delved into such subjects as the difference between imitative and non-imitative synthesis, percussive synthesis, animation of musical sounds, bell effects, and more. This installment concludes the article by covering additional examples of both imitative and non-imitative synthesis, as well as an extensive discussion on how to get the most out of LFOs.)

Other Examples of Imitative Synthesis

Imitative synthesis can involve sounds other than percussion. Crickets, for example, are easy to imitate. Because a cricket starts and stops its chirp suddenly, a square wave LFO is ideal for opening and shutting the filter or VCA. Use two oscillators in the 600 - 800 Hz range, tune them a half-step or so apart, and modulate them with a fast sine wave LFO. The modulation should be somewhat deeper than ordinary vibrato - a whole-step or so. Inverting the LFO on the way to one of the oscillators will help fatten up the sound, as will setting the two LFOs at slightly different speeds.

One other thing will help your crickets a lot: Use two or three of them at once, chirping at different speeds. (Multi-tracking becomes indispensable at this point.) Set the crickets at different volume levels, and give the quieter ones more reverb. Presto - instant summer night. Tricks like this will often give the listener the impression that the patch is very realistic, even if one of your "crickets" by itself isn't an especially good likeness. This is an important principle of imitative synthesis: If a sound is behaving like the acoustic sound it's intended to imitate, the ear will tend to assimilate it and identify it with that sound. If you have your bells strike the hour the way the tower bells at college do, they'll sound more realistic than if they just strike a note or two at random.

Another important point is this: Some of the things you try in the course of setting up an imitative sound patch might not take you in the direction of a realistic sound. But, bear in mind that the sound you discover just might be more useful musically than the realistic sound. Some of the most evocative sounds are the ones at the border of the known. They sound haunting and mysterious, yet elusively familiar. That is, they have an emotional meaning that communicates with the listener on an unconscious, pre-verbal level, even while the conscious mind is unable to exactly identify the nature of the sound.

Before leaving the subject of imitative synthesis, here's some advice for anybody who is tempted to imitate wind sounds: Don't. Wind (and its first cousin, surf) has become one of the instant cliches of electronic music. If, in spite of this caution, you feel you've got a valid artistic use for wind, it's not hard to make some. Just feed some white noise through a filter and modulate the filter with a slow sine wave LFO to simulate the rising and falling of the wind (see figure 4). A filter with voltage-controlled resonance would be especially useful for this patch, because as you raise the cutoff frequency you can increase the resonance with the same sine wave, giving the filter a slight shriek at the top of its rise. In addition to the noise, you might also want to mix in a couple of low-pitched oscillators at low levels for the wind's moan. Modulate these with the same slow sine wave so their pitches will rise slightly as the rest of the wind rises.

Figure 4: Wind

The other important characteristic of wind is that it's irregular in period. Rather than use a sine wave LFO at all, you might prefer to use a joystick or some other manual controller to modulate all these functions (filter cutoff, resonance, oscillator pitches) simultaneously. The wind sometimes has sudden surges, sometimes dies away into the distance, and sometimes rises to a sustained howl. If you do use an LFO, to avoid an overly predictable sound you could lay down several tracks of wind with different LFO speeds, or change the LFO speed and modulation depth by hand.

Basics of Non-Imitative Synthesis

The key to good-sounding non-imitative effects is really very simple: Just plug various things into one another and see what happens. When you find something that sounds promising, start thinking about ways to fatten it up. Generally, my non-imitative effects patches seem to use every function on the synthesizer and every patch cord in the house, because I can't help but wonder "now, what would happen if I hooked that up to it?" Of course, simple effects can be very effective too, maybe even more effective in the context of a whole arrangement. The point is just that you'll discover more if you indulge your curiosity and don't have too fixed an attitude about what is, or isn't, possible.

After you've been working with your synthesizer a while, you'll develop a feel for what connections are likely to lead to interesting results. But even then, you may still not know in advance what the patch will sound like when you've hooked it up. The fact that a modular synthesizer set-up retains its power to surprise the user with new sounds is one of its most important and enjoyable features. All the patches dealt with below are things I came up with in this seemingly haphazard intuitive fashion. They sound good to me, and they may give you some ideas of your own, but the only way you're really going to learn about synthesizer effects is to spend enough time with your equipment to develop an understanding of what sounds good to you, and how to go about getting it.

In the preceding discussion we've already touched on several ideas that are just as useful in non-imitative as in imitative synthesis. Perhaps the single most important idea is this: Oscillators can be modulated by an enormous variety of control voltages. What's more, these voltages can be processed in a variety of ways before they ever get to the oscillators. Oscillators can be modulated by other audio oscillators to produce complex tone colors (this technique is used a great deal in digital synthesis, where it is referred to as FM - frequency modulation). Two or three tone oscillators can be modulated by different voltages; by envelope voltages so that they rise or fall during the course of a note, by noise to turn them into pitched noise, and of course by the ubiquitous LFO - which we will now investigate in some detail.

LFO Techniques

Voltage controlled LFOs, which are unfortunately rare on "live performance" synthesizers, are a rich source of modulation. One of the simplest and most interesting things you can do with a modular-type synthesizer is to control an oscillator with an LFO and control the LFO with something else. Here's a simple example: Take the standard envelope that's triggered when you hit a key on the keyboard, and use that to modulate a sine wave LFO (see figure 5). Now you have a vibrato that instead of being static and mechanical—sounding speeds up at the beginning of the note and then slows down as the note dies away, more or less the way a violin player might impart vibrato to a string. Or, you could invert the envelope voltage so that the vibrato speeds up as the note dies away. If you're fortunate enough to have a velocity-sensitive keyboard and a voltage-controlled envelope generator, it's a simple matter to control the vibrato speed directly from the keyboard as you play.

Figure 5: Expressive Vibrato

Some other choices for modulating the LFO include another LFO to change the vibrato speed in a regular way, or a random sample-and-hold to change it in unpredictable ways. And, all this assumes that you're using the LFO's sine or triangle output to modulate a tone oscillator and generate vibrato. You can just as easily use the square wave output to create trills in the same variety of patterns, or the sawtooth output to create - well, sawteeth. Or you can apply the LFO voltage to some other module, such as the VCA, to produce volume swells.

Modulating the LFO with two other LFOs will give it a complex periodicity that hovers at the edge of being comprehensible, with results that can be either hilarious or somewhat disturbing. This will probably sound best when applied to a sustained oscillator tone rather than to a series of discrete notes. In other words, we're no longer talking about playing traditional music on a keyboard but pure electronic sounds. If we go on to route the LFO through a VCA before it gets to the tone oscillator, so that the vibrato will change in amplitude as well as in periodicity, things will start to get quite interesting.

This kind of patch seems to work well when the same LFO is also modulating the filter and there is enough resonance in the filter to give it response peaks corresponding to some of the formant frequencies of the human vocal tract (see figure 6). Don't worry if you don't know what these formant frequencies are - just nudge the filter cutoff frequency and the modulation amount until the filter starts to talk to you. If you've got the patch hooked up right, the filter should start to say, "Wow! Ooohhh, Wow!" No kidding. Last week I had a patch like this saying, "I want to be free! I want to be free!" Of course, much of this is in the ear of the listener; you might have heard the same patch saying something different. When it comes to non-imitative synthesis, subjectivity has a wide open field.

Figure 6: Talking Synthesizer

Okay, now that we have the LFO behaving in a fairly idiosyncratic way, let's use it for something besides modulation by tapping into the square or sawtooth output and using this is a clock to trigger the sample-and-hold (S/H). The S/H has become another of the cliches of electronic sound, but only in its simplest form (the only form accessible on most inexpensive synthesizers). When the S/H clock is ticking at a regular pace, usually fast, and sampling random noise at its input, what we get is the familiar random stepped voltage output. On a typical small synthesizer this can be applied to control the oscillator pitch or the filter cutoff frequency, and that's about it.

Let's hook the S/H to the oscillator (with any LFO disconnected for now) so that we'll hear the stepped voltage as pitches, but instead of using the regular S/H clock, let's trigger it with our syncopated LFO clock. The same clock should also be used to trigger the envelope that shapes the notes. The notes will have a more or less humorous effect as they bounce from one pitch to another at an unpredictable rate.

Now, disconnect all the other modulation inputs to the LFO, so it's pulsing regularly again, and then hook the random stepped voltage output of the S/H back up to control the LFO (see figure 7). This will have an immediate and perceptible effect: The higher the random step, the faster the LFO will hurry to its next tick - and thus, the higher the note sounded by the tone oscillator, the shorter the note will be, while the lower the note, the longer it will last. This is a psycho-acoustically powerful patch, because the high/fast - low/slow priority is found in much of traditional music. Think how many sixteenth-notes the violins in an orchestra play, as opposed to how many the double basses play.

Figure 7: Syncopated Sample and Hold

Now that you've heard this effect, hook the LFO's sine wave output back up to the same oscillator. If all goes well, it should begin to moan and hiccough in a positively eerie fashion.

The S/H is capable of some other tricks that you may find useful if you're tired of the same old synthesizer sounds. So far, we've only had it sampling noise to create a randomly stepped output. But if it has an appropriate patch point on the front panel, it can just as easily sample any other voltage we feed it. One of the most musically useful inputs turns out to be a sawtooth LFO. When the sawtooth is somewhat slower than the S/H clock (we're back to the normal regular-pulse clock ticking again now), the S/H output can feed a tone oscillator to create a scale-like staircase pattern. A sawtooth below 1 Hz and an S/H clock around 20 Hz will give us a flutelike flourish that has the advantage of not suggesting any specific tonality. Fed through an echo machine, such a flourish might be just the thing to lead into a higher-energy section of a piece.

As we speed the sawtooth LFO up, the steps of the staircase get further apart in pitch, and there are fewer of them in each rising (or falling) cycle (see related article in this issue - Ed). When the frequency of the sawtooth is less than twice the frequency of the clock, the staircase disappears, to be replaced by a phase interference pattern that is the aural equivalent of a moire pattern (or, a complex version of a Mozart alberti bass pattern). The finishing touch on this patch is to modulate the sawtooth LFO with a very slow sine wave LFO, causing it to change speed while the S/H clock stays steady (see figure 8). Now the alberti bass pattern, instead of repeating, will constantly shift, adding notes to make longer and longer arpeggios, then breaking into a microtonal scale that swoops down and back up, and so on. All by itself, the synthesizer is playing notes that seem to fall into meaningful patterns - though, as in the case of the "speaking" filter, it's the listener who creates the meaning by grouping or interpreting these sounds. I've always thought that three or four tracks of this kind of shifting pattern would be great for a fadeout on a fast, happy tune, but if you try it out, you might find some better use for it.

Figure 8: Sawtooth S/H with Evolving Phase

Non-imitative Percussive Techniques

Just about any combination of oscillators, ring modulation, and noise can be fed into a filter with a cymbal-like envelope to create an ugly mechanical burst. Or you can leave the filter's initial level high enough that sound always comes through, and modulate it with a repeating envelope for a nerve-wracking machine drone.

For something not quite so bizarre, turn the resonance on a filter up until it almost feeds back, and use an LFO square or sawtooth wave as an audio (not a control) input to the filter. The sharp edge of the LFO wave will make an audible click, which the filter resonance will draw out into a kind of metallic tap or woodblock-like knock. Tune it by adjusting the filter cutoff frequency, and change the rhythmic pattern by modulating the LFO. An LFO that has been randomized by modulation from the S/H (or three LFOs all modulating one another) makes a truly crazed percussionist. Alternatively, you could modulate the LFO you're listening to with another, slower square wave LFO. If you adjust the levels properly, the clicks will seem to be grouped as eighth-notes and triplets, because the LFO you're feeding through the filter will operate at two different speeds, one when the LFO modulating it is in the "up" portion of its cycle and the other when it's in the "down" portion. Be warned, however: Once in a while, this programmed percussionist will drop a beat, because the two LFOs won't be precisely synchronized.

Here's another idea: Use the square wave output from the second LFO (the one you're not listening to) to open and close the VCA, so that you'll get bursts of percussion followed by bursts of silence. Then take the sine or sawtooth output of this LFO and modulate the first LFO with it to make each burst of percussion change speed. Use a lot of sine or saw modulation in this patch, so the LFO going into the filter will rise from a slow clicking almost into the audio range before it's abruptly cut off. If all goes well, this patch should sound quite machine-like and ominous.

LFOs are also extremely useful for slowly altering the tone color of an ongoing event. Let's say you've set up a chord sequence on a three-stage, 16 step analog sequencer, with each stage controlling a different oscillator to give a sequence consisting of three note chords. The simplest patch is just to listen to all three oscillators all the time, but this can lead to aural fatigue pretty quickly. Fortunately, there are some easy solutions to this problem. You can route one of the oscillators through a VCA before it mixes with the other oscillators, and modulate the VCA with a slow sine or triangle wave, thus altering the amount of OSC 3 in the mix. If at the same time you use another LFO to modulate the waveform of OSC 2, and a third LFO to shift the cutoff frequency of the filter just slightly, while taking care to set these three LFOs at different speeds, your chord sequence will begin to take on a great deal of life. It will be hypnotically repeated and at the same time it will be continually varying in tone color, which paradoxically adds to the hypnotic effect.

As long as we're on the subject of sequencers, don't forget that a sequencer clock doesn't have to tick at a steady rate. With a three-stage sequencer, it's easy to use two of the stages to play pitches on the oscillators and the third to control the speed of a voltage-controlled clock. Syncopation and odd time signatures are one possible result. Even more intriguing is the possibility of setting up a riff whose metrical values are slightly off. On a digital sequencer, this is even easier to manage - just play something with a lurching syncopation, and hit the repeat button. You'll have a hypnotically repeating pattern that you can't quite tap your feet to, like a broken record. Improvising a solo over such a riff can lead your melodic thinking into entirely new areas.


We could go on listing patches, but the basic concepts should be clear by now. However, there's still the question of how to use these new sounds musically. While this could take another article in itself, here are a few random suggestions that you might find useful.

Synthesizers are so clean-sounding they sometimes don't blend in well with other instruments when recording. Echo will usually help this - or you might want to run the synthesizer through a guitar amp and mike the amp. Basically, anything that will introduce a touch of distortion and a physical quality to the tone will help a lot.

Concerning where to put effects in a piece of music, it's always a temptation with any new toy to use it everywhere you possibly can. But if you're not careful, your arrangement might end up sounding like a Christmas tree. The solution here is probably to treat the synthesizer the way you would any other supporting instrument. If it's an adjunct to the drum kit on a particular tune, listen to how the drummer is developing his or her part, and cue in your synthetic rachet or cowbell at a point that will make sense in conjunction with the snare drum and hi-hat. When a new section of the tune arrives, the drum part will usually change, and the synthesized percussion should change in response.

Like any other instrument, an effects synthesizer should be applied tastefully, with an awareness of how the whole arrangement fits together. Unless the effects are the focus of the tune, the synthesizer should probably be used for no more than three or four different types of events in any one tune. One of these events might be a major hook - a beeping that makes the chorus so unsettling, for example - while others might be purely supportive and very much in the background. The same principle applies to classical music synthesis; only the terms need to be changed. Synthesizer effects can be extremely complex and alien, or they can be very simple, but in either case it's important to remember that they aren't an end in themselves. They're a means to the end of creating good music.

When it comes to music that's played entirely on synthesizers, you obviously have more latitude for the lavish application of effects. But even here, you'll need to consider what the character of a given piece of music is, and which patches will further enhance that character. Is the mood insistent and urgent? Is it murky, misty and mysterious? Is it placid and pleasant? Each mood calls for different effects. In fact, a good exercise might be to decide on an emotional meaning first and then try to set up a patch to convey it.

In the last analysis, only a thorough familiarity with the capabilities of your own equipment will tell you how to achieve the effects you want; you may not have equipment comparable to what I used to set up the effects described in this article. But no matter how limited your equipment, by applying the principles I've outlined that equipment will probably be capable of more than you're using it for currently. So start messing with those knobs and switches. And don't forget to keep your ears open.

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Polyphony - Copyright: Polyphony Publishing Company


Polyphony - Jul/Aug 1981

Donated & scanned by: Mike Gorman


Synthesis & Sound Design


Modular Synthesizer Effects

This is the only part of this series active so far.

Feature by Jim Aikin

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