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Music Modules for NON-Keyboardists

Article from Polyphony, April/May 1978


Walk into a room full of musicians and mention the word synthesizer. Chances are that you will meet with about as many opinions as there are people in the room. Obviously, the keyboard artists are going to be pretty much in favor of the device. And why not?! Most of the synthesis equipment rolling off the assembly lines is aimed directly at the keyboardist. With the widespread use of synthesizers in bands, many of the other musicians have developed an interest in the possibility of using synthesizer equipment with their own instrument. However, in many cases the musician gets a bit confused when confronted with all the new terminology. But even worse, he doesn't know where to turn when he walks into his local music store, heads to the synthesizer department, and only sees row after row of keyboards staring at him. Well, let's take a look at some of the effects that are available to non-keyboard musicians, and how to use them.

The body of musicians which would most easily be initiated to the world of synthesis are probably the guitarists. Actually, guitarists were probably the first modern synthesists due to the barrage of effects boxes which were created for them back in the '60s. Fuzz boxes, wa-was, treble boosters, octave boxes, and talk boxes were all available before the turn of the decade for the adventurous experimental guitarists. And in recent years, even more effects units have become available. Therefore, it should be relatively easy to introduce the guitarist to a modular, patchable effects console which would eliminate most of the standalone effects gadgets he has lying at his feet. Using synthesizer modules will offer the guitarist increased flexibility, future expansion capabilities, and possibilities for increased complexity of effects.

A closely related group of instruments includes the instruments which can have contact mikes or pickups installed to convert them to electric instruments. These include violin, saxophone, banjo, autoharp, acoustic guitars, trumpet and many more. The module system array for these instruments would be the same as for guitar, and would operate in the same manner, but the musicians would probably require a bit of introduction to the techniques of signal processing.

A third group of potential synthesists is drummers. Drum sensor systems are actually rather easy to build, and can consist of custom built "drum-type" sensor pads or they could actually be converted acoustic drums with some type of pickup mounted on them. The module array for a drum package would be slightly different from a guitar-type system, and it would be operated in a different manner also.

Let's take a look at the types of modules which are particularly suited to use as processing elements for external signals. First of all, the audio processor modules such as VCFs, VCAs, reverb, and balanced modulators are immediately applicable to external signals. All that is involved is patching your external signal into the module rather than the typical synthesizer signal source such as VCOs, or noise sources. The VCFs can be used to do wa-wa effects, pseudo-phasing, treble or bass boosting, and much more. A VCA acts like a voltage controlled volume control, and lends itself to effects such as volume pedals, attack delay units, generation of new percussive or soft envelope timing structures, noise gating, and tremelo or amplitude modulation effects. Initially, you may feel that a reverb unit in an effects system may be a redundancy if you have a reverb unit built into your amp. Not so! With a separate reverb unit which can be patched into various points throughout the effects unit, a myriad of effects can be obtained which are absolutely impossible with a standard guitar amp reverb. Balanced Modulators can do a number of jobs from giving your instrument a "metallic" sound, to making the strings of your guitar sound like rubber bands, and so on. One of the biggest problems with balanced modulators is that they so drastically alter the input signal that a great deal of time and patience must be spent on trying to use the effect artistically — and not overdoing it.

Controller modules are required to "tell" the processing modules what you want them to do. There are a wide variety of controller modules available, and when used in conjunction with each other, some incredibly complex control functions can be programmed. One of the simplest controller devices is a bias supply such as in the Paia 2720-7 Power Supply. A bias supply is used to set a fixed voltage output which you won't need to change. For example, you could use a bias supply to control a VCF. The result would be like a tone control — set the bias control to get the desired amount of "sharpness" in your tone, and then leave it. Another type of controller which should be familiar and easily implemented by the guitarist is a Foot Pedal control. These are most commonly seen as volume pedals and wa-was. Minimal parts and labor are required to convert a basic volume pedal into a multi-purpose pedal which can process audio or control voltages, or can be used as a variable source of control voltage with the pedal supplying it's own voltage source. For more information on this easy modification see issue #2-76 of Polyphony, page 9. It is highly recommended that the prospective "guitar synthesist" invest in one of these goodies as well as the following item. These two devices are going to be the most important in the entire modular system. An Envelope Follower is the one module which is directly responsible for allowing the guitar or other external signal to trigger and control the various parameters of the effect you have programmed. Let's initially take a few lines to define our terms. An Envelope Follower is a circuit which senses the "volume" of an input signal and puts out a varying DC voltage which is proportional to the "volume" changes at the input. Most envelope followers will also put out a trigger gate or pulse which can trigger external equipment whenever a signal is present at the input. When the signal drops below a certain level, the trigger output will then disappear. NOTE that the envelope output is a variable fluctuating voltage from 0 to about positive 5 or 6 volts, while the trigger output is always a fixed voltage jumping from 0 volts to positive 5 volts or more. One point of frequent confusion is the commercial availability of certain types of sound modifier products which are also called envelope followers. These are filter devices in which the filter (or wa effect) is variably swept as the input signal is changed in amplitude. In actuality, these devices are envelope followers which are driving VCFs. They are NOT just the basic envelope follower, and in most cases they don't make the variable voltage and trigger available at the rear for use with external voltage controlled equipment. Another point of importance is the frequent confusion between envelope followers and pitch (or frequency) followers. Recent (so-called) guitar synthesizers frequently feature pitch followers and circuitry which allows the machine to determine which note is being played by the guitarist, converting it to an appropriate control voltage, and using the voltage to drive a VCO to a pitch identical to what the guitarist originally played. For the purposes of this article, we need not get into how this works — or whether it even works at all. This would take an entire article in itself. The important point is that the Envelope Follower does not sense pitch changes at all, only changes in amplitude.

FIG. 1: ENVELOPE DRIVEN FILTER


Using only the envelope follower variable output in conjunction with the previously mentioned audio processing modules, several interesting effects are available. With the envelope output feeding a control input on a VCF, the envelope controlled filter effects which are currently so popular can be easily obtained. Every time a guitar string is played, the envelope follower will detect the sudden increase and gradual decay of the guitar output and will output a voltage which will cause the filter to suddenly jump to a "sharp" high frequency setting and gradually fall to a mellow, bassy filtered tone. See figure 1. This is basically the effect which the commercial "envelope follower" devices create, however, we can already begin to appreciate the added power of a modular effects system by realizing that not only the standard bandpass filter type of wa-wa is available, but also low pass and high pass outputs if you are using a multimode filter. Additionally, most filters will have adjustments available for filter "Q" or resonance. This is something you won't find on most of the inexpensive envelope-filter units! And the versatility has only begun. Note that most modules have multiple control voltage inputs so you can sum together several independent control sources. With this in mind, you can use your control voltage pedal to operate the VCF as a wide-range, multimode wa-wa pedal... perhaps even in conjunction with the envelope follower. Another variation could be used to get pseudo-phasing effects. Through the use of an external mixing circuit, the low pass and highpass outputs of a multimode filter can be combined to create a NOTCH filter which will sound very much like a simple phaser. Using your foot pedal, you can achieve manually controlled phaser effects rather than the fixed periodic sweep of most commercial phasers. Or, how about using the envelope follower to get phasing sweeps which are proportional to how loud or how hard you are picking. I always think it makes an effect seem much more like an integral part of the music when it is directly related to the dynamics of the music such as in this set-up. Give it a try. I think you'll find it a bit more appealing than the repetitive sweeping of a phaser over its entire range.

When the VCA is substituted for the VCF above, the two primary modes of operation are as an expander and a volume pedal. When the foot pedal is used to provide the control voltage required to vary the VCA level, it looks like a waste of equipment since the pedal itself can be used as a volume control. The primary advantage would be that rather than feeding an audio signal across the stage (perhaps alongside power, lines or lighting equipment lines, which are notorious for inducing noise in audio lines), you are feeding only a slowly varying DC voltage. Your audio signal remains inside your little box of modules, safe and sound. An expander is generated by using the envelope output to vary the VCA level (See figure 2) in proportion to the input signal, causing the original dynamic range to be increased by a factor of two. This gives the signal added punch and definition. Using the envelope follower step trigger output to control a properly calibrated VCA will act as a simple noise gate device. NOTE that the VCA must be properly calibrated, otherwise the fast switching of the step trigger being fed into the VCA control input may cause a pop. If you are using a number of signal processing devices which are adding to your noise level, a noise gate could be the answer to your quest for silence between songs!

FIG. 2: EXPANDER


From this basic starting point, additional controller modules can be added to make your special effects unit a bit more 'super'. Adding an ADSR Envelope Generator will allow you to preset a timed sequence of sweeping voltage which can be used to control any of the modules which are voltage controlled. When an ADSR is triggered, the output begins rising from 0 volts towards 5 volts at a rate that is set with the Attack control. When the Attack peak is reached, the voltage Decays at the same rate you selected until the present Sustain level is reached. At this point, the output holds until the trigger voltage is removed from the input. The output voltage then falls through the Release period until the (output is again 0 volts. Using these characteristics, the step or pulse trigger output of the envelope follower can be used to trigger the Envelope Generator, which will in turn sweep a filter, vary the level of a VCA, and so on. The effects achieved with these types of patches are similar to the use of the 'envelope' output from the Envelope Follower, except you no longer have the "randomness" related to the varying input amplitude. Each generated envelope will have exactly the same timings, dynamics, and characteristics. Using the Envelope Generator to control a VGA can produce some good "bowed" string effects or reverse tape simulation if you set the Attack for a moderate to long timing. See figure 3. This patch also tends to work best if the Release is set to minimum. This way, the Envelope Generator will reset immediately after the input signal has been damped or removed, and the system will be ready for the next note. The ADSR/VCA combination will also generate a noise gate which is much less prone to popping as mentioned earlier. This would be the recommended noise gate configuration.

FIG. 3: ATTACK DECAY OR "BOWED" ENVELOPE SHAPING


Adding a Low Frequency Oscillator to the system will allow any of the voltage controlled parameters to be periodically swept at various rates and with various waveforms. We could go back to the NOTCH filter which we discussed earlier, and use a LFO to continuously sweep the effect, just like the commercial phasors. Alternatively, the LFO could be used to automatically sweep the VCF or control the VCA for tremelo effects. By itself, the LFO as a controller tends to be a bit (dare I say it) boring. BUT, when summed with or processed by additional modules, this can be one of the most useful circuits. To get an unending variety of low frequency waveforms, the LFO output can be used to repeatedly trigger an Envelope Generator. With minimum Attack and medium to long Release, a falling ramp wave can be generated. Conversely, an upward ramp is easily generated. These techniques can be used to also generate triangle-type waves and square waves for control purposes. And I haven't even mentioned repeating ADSR shape waveforms yet! There's a lot of fun to be had with this patch! See figure 4.

FIG. 4: MULTI-WAVEFORM FILTER SWEEPS


Adding the Inverter will greatly increase the possibilities from any given set of modules, as you will now have not only the original audio and control waveforms available, but also their inversions. Instead of upward deflections of the filter with an Envelope Follower or Envelope Generator, you will now be able to achieve downward sweeps. Using any of the controller devices, you can feed the original controller output to one effect module (let's say a VCA), and feed the inverted control signal to an identical effects module which is connected to a second output amplifier. In the case of VCAs, this will cause a panning effect as the controller output changes. See figure 5. If the controller is an Envelope Follower or Envelope Generator, you will get one "pan" for each note. With a LFO, you will get continuous panning, and so on. This same patch could be used to route the signal between two different effects or to manually select the effect "depth" with a foot pedal control voltage.

FIG. 5: AUTO-PANNING


Another interesting mode of operation is to use the input signal (guitar, mike, or whatever) to control some other signal. As an example, we can use the white noise source which is built in to the Paia LFO to augment the basic input signal. If the input is detected by an envelope follower, the trigger output (pulse trigger this time) can be used to trigger an ADSR which is set for minimum attack, minimum decay, maximum sustain, and 25% to 50% release. The resulting envelope can be used to control a VCA which has the noise source as an input. The VCA output is then fed to the external amp along with the input signal. The result? Every time a note is played on the instrument, it will sound as if a cymbal was played simultaneously. There will be a short decaying burst of "hissing". To use this technique in a more interesting patch, substitute the noise source for a reverb unit. Set the reverb output mix so you get ALL reverb and no normal signal. Feed the input of the reverb with the input signal which is feeding the Envelope Follower. The input signal should also be fed to the final amp as usual. Now, every time a note is played, there will be a sudden burst of reverb which will shortly die away. See figure 6. This patch can give a kind of spooky effect, because it sounds as if the size of the room is changing as you are playing. One more variation of this patch would be to delete the ADSR, and use the variable envelope output to directly control the gain of the VCA. This gives the same basic effect as before, except the effect depth is now responsive to your playing technique, breath inflections, and dynamic variations. Don't forget the use of the inverter for applications such as these, also. The inverter could be used to invert the envelope control signal (whether it is from the envelope follower output, or from the envelope generator makes no difference) such that there would be NO reverb when an input signal was present and the reverb would then fade in as the input signal got softer or was removed. Bizarre, to say the least!

FIG. 6: ENVELOPE DRIVEN REVERB


All of these effects could be achieved with what I would consider to be a basic processing package. For starting your experiments in signal processing synthesis you should get a 4761 wing cabinet, a 2720-7 power supply (so you'll have the bias supplies for fixed parameters), a 2720-11 envelope follower, a 2720-12 inverter, a 2720-1 VCA, a 4712 reverb, a 2720-5 LFO/noise source, a 4740 ADSR, and a 4730 multi-mode filter. Also remember that a foot pedal should be included as an important part of the system even though it is not part of the module cabinet. With this system, you should be able to blow away most of the people who are attempting processing synthesis using an array of foot pedal effects devices.

Another common question from people interested in signal processing concerns an easy way to use footswitches to turn an effect on and off. The best way involves using the footswitch to actually supply a control voltage or logic signal rather than actually switching the audio signal. The reasons for this are the same as when we were discussing use of a pedal and VCA for a volume pedal. Rather than get into all the details of analog switches and how to build a footswitch system, I refer you to Craig Anderton's book, "Electronic Projects for Musicians" ($6.95 from Guiter Player Productions, (Contact Details)) in which Craig describes an electronic footswitch system. This would perfectly suit the experimenters needs, and a kit is even available for the project.

Drummers interested in expanding the capabilities of their "skins" have recently taken to drum triggered signal synthesis systems. For this type of application, the package described previously is still valid with the exception of the requirement of a VCO. For drum type sounds, the VCO is required to produce the drum "strike tone". Further, the two waveforms most likely to be used to approximate traditional drum sounds would be sine and triangle waves. These waves are nearly pure (meaning that they have little or no harmonic content) and should need no filtering, so we can exchange a 4720 VCO for the 4730 VCF mentioned in the package outlined previously.

The most requested electronic drum patch is the "bending" conga drum effect. To achieve this effect, a drum sensor is used to trigger the ADSR which has been preset for minimum attack, minimum decay, maximum sustain, and moderate release times. The variable ADSR output should be summed into the VCO control inputs along with a fixed bias voltage from the power supply. See figure 7. The bias supply is used to initially tune the VCO, while the ADSR variable output sets the "bend" range. The sine wave output of the VCO is fed to a VCA which is being controlled by the full-range output of the ADSR. The VCA output goes to the external amp.

FIG. 7: "BENDING" CONGA DRUM


To backtrack a few lines, we need some type of trigger input from the drum sensors. There are several ways to get "solid-state" drum sensors which don't generate any sound of their own. However, for the initial experimentation of a drummer who already has a trap set, probably the best route to take would be to detect triggers from your existing drums. For our purposes, you could use an inexpensive contact mike, or a small mike like you can get to use with portable cassette recorders, etc. This can just be taped to make contact with the shell or bottom head of the drum which you wish to make a sensor. The mike can then be run through an envelope follower to generate one output proportional to the drum dynamics, and another straight trigger signal. In most cases, you will need to work with the sensitivity control on the envelope follower to make sure that the vibration caused by playing nearby drums will not falsely trigger the electronics array. If you have a particularly sensitive microphone, you may even wish to wrap it in a rag or place a thin piece of foam rubber between the mike and drum to make it less sensitive. With the sensor problem out of the way, you have a clear road to the latest in drum effects units.

On the commercial Syndrums, a switch is provided to cause the drum to bend up or down. In our system, we can use the inverter module to change the ADSR output from a falling VCO bend to a rising bend. The LFO can also be summed into the VCO to give your drum vibrato. The noise source can be processed through an envelope controlled VCA to add a "snare" effect to any of your drums. You could perhaps use the pulse waveform output of the VCO, with the drum triggered ADSR causing a sweep of the pulse-width modulation. This would give a raspy, phased drum effect. And the tricks with the reverb unit mentioned earlier are equally as useful on the drum system as on the processing system. There is a lot of power to be discovered in a modular drum synthesizer. As usual, if one drum sensor and module package is neat, an array of two, three, or more could be... hazardous to your sanity?... lethal?... Well, at least interesting, wouldn't you say?!


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Previous Article in this issue

Modify Your "Phlanger"

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To Phase or to Flange


Publisher: Polyphony - Polyphony Publishing Company

The current copyright owner/s of this content may differ from the originally published copyright notice.
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Polyphony - Apr/May 1978

Donated & scanned by: Mike Gorman

Feature by Marvin Jones

Previous article in this issue:

> Modify Your "Phlanger"

Next article in this issue:

> To Phase or to Flange


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