Construction kit

SOME MUSICIANS WERE MADE for the geekier, visually barren yet audibly amazing DIY programs such as Cycling '74 Max/MSP or AudioMulch. These are often
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SOME MUSICIANS WERE MADE for the geekier, visually barren yet audibly amazing DIY programs such as Cycling '74 Max/MSP or AudioMulch. These are often the same people who happen to know a thing or two about writing complex computer code. If you, on the other hand, are a complete beginner to modular synthesis, prefer a bit of eye candy with your synthesizers or simply love classic synths, then this article is for you. Here, you will explore the basics of building synthesizer patches from scratch using Arturia's exquisite software rendering of the legendary ARP 2600.


It should be mentioned that unlike some other modular synths that rely on patch cables to produce sound, the original ARP 2600s (as well as the 2600 V emulation) are semimodular. That means that, like nonmodular synths (such as the Sequential Circuits Prophet-5, Korg Polysix or Roland Jupiter-8), they contain an internal matrix that connects their different modules in a pre-determined sequence. But they also contain audio and modulation patch points that can override this matrix. Therefore, like its forebear, 2600 V can generate sound with or without the use of cables. Because the topic at hand is programming modular synths, for the sake of clarity, I will (mostly) treat the ARP as though it were fully modular.


As a starting point, you will need a patch that produces no sound. The points of origin of sound with most synths is their oscillators. In the case of 2600 V, these are the three VCOs, or voltage-controlled oscillators. Each is capable of producing tone, so start by turning them off and clearing all cable connections if any are present. Then, position all vertical potentiometers all the way down, paying particular attention to the 14 sliders in the oscillator sections (VCO1, VCO2 and VCO3) and the eight in the filter section (VCF, or voltage-controlled filter). If a MIDI controller's keys are now pressed, no sound is made.

To become familiar with the different sounds of the oscillators in their most naked forms, set all three five-position range switches (marked 4, 8, 16, 32, LF) in the oscillator sections to the same value; use 16 as a starting point. In the case of 2600 V, VCO1 can create sound with sawtooth and square waves while VCOs 2 and 3 can be set to triangle, sawtooth, sinusoid (or sin) and PWM (pulse width modulation). By connecting a cable from the Saw output of any of the three VCOs to the Pan input (situated between the left in and right in on the far right), you can hear the uninterrupted raw tones of the oscillators' saw waves. The sound from each oscillator is identical, as long as the range, Init(ial) Osc(illator) Frequency, Fine Tune and Pulse Width controls are set to the same relative positions. By connecting any of the other VCO audio outputs (Square, Triang, Sin, Pulse PWM), you can hear their respective raw tones and notice that they, too, sound identical to one another (with one exception — VCO1 is the only oscillator that sports a square wave).

Performing just this initial patch is not very useful, as the tone produced is a steady single pitch that is unaffected by keys pressed on the keyboard (or MIDI controller). That is the next step. Starting with VCO1, if you connect the Square output to the Pan, then connect a cable from the Keyb CV Out X1 (on the keyboard module) to the Kbd CV input on VCO1 and raise the corresponding linear pot, you will hear the pitch gradually go up or down (depending on the range setting) until you reach the top. Then, when the keys are pressed, they will play in pitch. If, instead, you connect the Keyb CV Out X4, each half step played on the keyboard will sound a note that is four semitones higher than the last note played. Still, this is not much of a useful patch, given that it's a bland and continuous tone.

Now, the filter (VCF) and envelopes (ADSR and AR) come into play. First, move the VCO1 Square output from the Pan to the VCO1 input in the VCF section, and connect the VCF Out to the Pan input. Then, set the filter-type switch (denoted by five settings — LP 24, LP 12, HP 12, BP 12 and Notch) to HP 12. Without any other changes, no sound will be heard until the VCO1 level fader on the VCF is raised. If it is raised to max and the Init(ial) Filter Frequency pots are all set to the far left, the sound should be nearly identical to what was previously heard when the VCO1 was connected directly to the Pan. Next, connect the ADSR Out to the VCF's ADSR input and raise its fader to max. If the ADSR faders are set to their lowest values, this won't affect the sound, but as soon as you start moving them around, an effect on the sound will be heard. Then, switch the filter type from HP 12 to LP 12 or LP 24. This will dampen the sound quite a bit, or you may hear silence depending upon the current ADSR settings. Now, you can begin to shape the tone with attack, decay, sustain and release (ADSR) times and hear a playable keyboard tone instead of a steady, monotonous signal.

To begin hearing the vast potential inherent in modular synthesis, connect another cable from the Keyb CV Out X1 to the Kbd CV in on VCO2 and raise its linear pot, but switch the VCO2 range switch to 4 and its Init. Osc. Frequency to -5 semitones. Now, connect the VCO2's Sin output to the VCF's VCO2 input and the VCO2's Saw output to the VCF's VCO3 input. By raising the corresponding linear pots for VCO2 and VCO3 in the filter section, you will now hear a three-voice tone. By switching the VCO1 range switch from 16 to 32, a wider harmonic separation between the tones is heard.


Although you may now have a playable tone, there is still nothing especially striking about it. So it's time to add some modulation. Note that audio and modulation connections are interchangeable; the main difference is that modulation sources are typically too low for the human ear to hear. For this example, oscillator 3 will be used as a modulation source. By connecting the Pulse PWM output of VCO3 to the Control VCO2 input in the Filter section and raising the corresponding linear pot, you will use the PWM as a modulation source and impart a fluttering sound to the tone. VCO3's Range switch should be set to LF (low frequency); the Init. Osc. Frequency should be set to max (30.0 Hz); and the Pulse Width should be set to 50 percent. If the VCF's VCO2 input level is set all the way up, after a note has reached its perceived full decay, a resonant hum will still be heard at a very low level. This can be tamed by lowering the VCO2 level. Testing out various Init. Osc. Frequency and Pulse Width settings on VCO3 can create interesting varieties of modulation.

Another simple example of added modulation is FM (frequency modulation). By connecting any of the oscillators' outputs to any of the other oscillators' inputs, the sending VCO's source modulates the receiving VCO. For example, if you connect the Saw of VCO1 to the ADSR inputs on VCO2 and VCO3 and raise their corresponding pots, an interesting blend of roughness enters the sound.


Up to this point, you have been dealing mainly with three fundamental modules of synthesizer sound creation (the oscillators, the filter and the ADSR envelope), bypassing one of the other basic components of synths: the amplifier (the VCA in 2600 V). This section allows for volume balancing among different sources. If you move the VCF Out connection from the Pan to the VCA section's VCF input, move the ADSR Out connection from the VCF section to the VCA's Lin ADSR input and finally connect the VCA Out to the Mixer section's VCA input, you will essentially have the same sound available, but you can now mix the different incoming signals and add to them. If you raise the pots in the VCA section for VCF and Lin ADSR to maximum and do the same for the VCA in the Mixer section, you have the same tone and volume as before adding the amplifier to the chain. As an example of radically altering that mix, raise both linear pots in the Ring Mod section to max, connect VCO2's Sin output to the VCO1 input of the Ring Mod, and connect VCO2's Saw output to the VCO2 input of the Ring Mod. Then, connect the Ring Mod Out to the VCA's Ring Mod input and raise its corresponding pot. What you end up with is a whistling sound that modulates in and out of the mix for some added character.

LFOs (low-frequency oscillators) are integral to many synthesizers, both modular and nonmodular. LFOs are typically used as a source of modulation, due to their extremely low frequency output. Although all three VCOs in ARP2600 V are capable of low-frequency oscillation, the LFO section is dedicated to that task. To hear its powerful effect, first raise the LFO Speed and Vibrato Depth pots. Because the LFO is hard-wired, you will hear its effect on the entire patch without connecting cables. Next, connect the LFO's square output to oscillator 1's VCO2 input and the LFO's saw output to oscillator 2's VCO1 input. By then raising both corresponding linear pots on the oscillators, the resulting patch now sounds like some sort of futuristic helicopter hovering in space.

This piece has barely scratched the surface of what you can do with modular synthesizers, Arturia's ARP2600 V included. The purpose here is to present some of the foundations of building modular patches using oscillators, filters, envelopes and amplifiers. Certainly, a bit of logically applied know-how is the foundation for this endeavor, but experimentation is truly at the heart of modular synthesis. If you already own one of these beasts yourself, then take your time and get to it! And if you don't, perhaps it's time to change that.