Modular Analog Synthesizers

Looking through old documents, I found an article with which I started a passion for analogue modular sound synthesis. I want to inspire you too.

The article, unfortunately, was only kept locally, and the original is not opened. Thanks to the author - an unknown Ambush . The text is slightly adjusted and revised by me.
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Electronic music synthesizers can be divided into 4 classes.

1. Analog synthesizers
2. Digital synthesizers
3. Opto-electronic synthesizers
4. Mechanical or pneumatic synthesizers.

Today, dear friends, we will talk with you about analog synthesizers.
Analog synthesizers can also be divided into 4 types according to the method of formation

Subtractive

Subtractive means synthesizers with a rich spectral composition of the original oscillators (spectrum generators, noise generators). Spectral-frequency processing in these synthesizers is carried out by cutting out the excess spectrum using voltage-controlled filters, and the amplitude-time characteristics are changed by means of voltage-controlled amplifiers and time function generators.

Additive (harmonic synthesis)

Harmonic synthesis is the most accurate and subtle way to synthesize sound. This is done by summing sinusoidal functions, where each function can vary arbitrarily amplitude and frequency. To build such a synthesizer, an Nth number of generators of such functions is needed (from about 40 and more, on average, somewhere around 256 generators).

FM synthesis

I will write in brief, because I do not know how to enter here any formulas. Figuratively speaking, this is when one generator with an arbitrary function modulates the second generator also some functions, and it in turn can modulate the third generator, and that in turn the first generator, etc. You can roughly calculate the number of combinations of eight-band FM synthesis by yourself :) The generators there can be modulated in any order and sequence.

Any original and original methods of synthesis

Ways that due to certain circumstances have not found further application. There are so many of these methods that it probably does not make sense to consider them.

Subtractive synthesis

Subtractive synthesizers are also divided into 2 classes. These are concert synthesizers and studio synthesizers. But the principle of their construction is the same. This method was invented in 1964 by Robert Moog, although devices of this type existed long before its discovery. These devices were called analog electronic computers. Robert Mug only systematized and adapted this type of analog machines for musical use. Analog synthesizers (today we will consider only a studio analog synthesizer) as well as electronic computers consist of modules.

Keyboards, sequencers and joysticks ...

1. Keyboard is a keyboard :) It can be either polyphonic or monophonic. The keyboard is a source of calibrated control voltage and control pulses (“start”, “strobe”, in English GATE ). A short control pulse "start" appears at the moment of pressing the key. The control pulse "strobe" is equal to the time duration of pressing a key. These pulses are needed to synchronize and trigger control blocks in the synthesizer. There are keyboards that have an additional control output voltage, which is determined by the force of pressing the key. Such keyboards are called dynamic and are very expensive, but allow the musician to show all his performing skills.

2. Ribbon Controller is a strip of special material, by sliding your finger along which you can achieve a smooth glissando effect.

3. Sequencer is a sequencer. They are analog and digital.

Analog sequencers are software devices that allow the output to receive a control voltage multiplexed by an analog device with potentiometers. The position of the angle of rotation of the potentiometer knob determines the control voltage. With sequencers, not only the frequency (the scanning speed of the potentiometer matrices), but also the duty cycle (the ratio of the pause for the duration) can change. The number of scanned potentiometers can be arbitrary. The number of channels of these cells, too. It all depends on the free space on the front panel of the sequencer, i.e. its sizes:) As a rule, the memory capacity of such sequencers is not large and usually varies from 8 to 32 cells.

Digital sequencers are digital storage devices that memory code from a keyboard scan matrix. They can have a huge amount of memory and memorize the score of both polyphonic and monophonic music. Just as in analog sequencers, you can edit the tempo and randomly change the duration and frequency of the note.

4. Joystick is a joystick. As a rule, these are two potentiometers, which are at an angle of 90 degrees, mechanically designed in such a way that they allow one lever to move freely along two coordinates — X and Y, i.e. allow one movement to control two parameters at once. There is also a wheel called Pitch Bend. Serves in order to receive "suspenders".

Generator Modules

1. VCO is a voltage controlled generator, as a rule it generates 4 types of pulses - these are sawtooth, triangular, rectangular and sinusoidal voltages. Each pulse shape has its own specific spectral characteristic, which is why so many different forms are used for this. For example, a rectangular voltage may be able to change the pulse duty ratio (the ratio of the pause to the pulse duration) depending on the control voltage, which allows you to change the spectral composition of these pulses. All these pulses are usually mixed in a mixer and fed to a balanced modulator or voltage controlled filter.

2. Noise is a noise generator. Studio synthesizers typically use a white noise generator and a pink noise generator.

3. An LFO is a low-frequency generator designed to control VCO, VCF, and VCA units. As a rule, the output function of such a generator is quite complex and allows you to vary these output functions over a wide range, from a sinusoidal function to a triangular or rectangular, in a large low frequency range - 0.01-100 Hertz. These devices, in turn, can also be voltage controlled and modulated by the same generator as himself. But, as a rule, such a generator is triggered by a “strobe” or “start” signal, correlating with the functions of the keyboard, sequencer, and other devices. As an LFO, you can sometimes use ADSR, on which you can pre-build the necessary function.

4. ADSR is an envelope function generator.
A - ( attack ) - the initial phase, the rise
D - ( decay ) - phase of the transition of sound in a steady state
S - ( sustain ) - phase of "support"
R - ( release ) - after-sounding
It is used to control the VCO, VCF, VCA, as well as the LFO. There are ADSR blocks with a large number of elements approximating the function - from 4 to 8. Sometimes these modules are performed with a variable level of elements, i.e. Attack time can be set by voltage from some external time function generator, such as an LFO or a sequencer. It is also interesting to use a keyboard for this purpose. In this case, the attack time will vary along the entire length of the sound-height row of the keyboard. An ADSR is typically triggered by a “gate” signal from the keyboard or sequencer. It can also be triggered by a square wave with an LFO. The output function of ADSR is sometimes interesting to invert.

5. Sample & Hold - random sample generator. Together with two Noise and LFO generators, it is intended to create a random sequence of low-frequency pulses that are used to control other synthesizer functions. As a rule, it has a very colorful sound. Sometimes, instead of the Noise generator, you can use any other spectrum - VCO, VCF, VCA, another LFO. (I do not agree, the module strobe remembers the signal from the input and keeps it at the output, and the random sample generator is obtained from S & H just by connecting noise and LFO, but there may be other uses)

Voltage Controlled Modules

1. VCF is a voltage-controlled filter that serves to change the spectral-time functions depending on the control voltage. They are divided, as a rule, into 3 classes:

- LPF - low-pass filter (LPF).
The bandwidth of this filter defaults to the low frequency region of the spectrum. As the control voltage rises, the cutoff frequency of this filter moves to the high frequency range.
- HPF - high-pass filter (HPF).
The bandwidth of this filter defaults to the high frequency region of the spectrum. As the control voltage rises, the cutoff frequency of this filter moves to the low frequency range.
- BPF - bandpass filter (formed by the sequential inclusion of the two previous filters) (bandpass filter).
The bandwidth of this filter can be in an arbitrary region of the spectrum and is a bandwidth whose width depends on the quality factor of the filter. The quality of the filter (Q) can also be controlled by the control voltage.
As a rule, filters of studio synthesizers use filters from 2 to 8 orders of magnitude. One order is 6 db / okt. Usually, 4-order filters are used, i.e. 24 decibels per octave.

2. VCA - voltage controlled amplifier. Used to control the function of amplitude-time characteristics. Usually works together with an ADSR generator and LFO. The noise parameters of such an amplifier are very important. The components used to make such an amplifier must be very high quality and have a very low noise figure.

3. RM is a balanced modulator (usually a simple 4 quadrant multiplier). Used to give the sound of originality and color.

Auxiliary modules

1. Mixer is a mixer. Required to mix the Nth number of sound or control signals. As a rule, these are small mixers with 4 to 8 channels. There are mixers that perform summation and subtraction functions simultaneously. In the middle position of the potentiometer, the channel output voltage is 0. When turning from 0 to the left, the signal is added to another channel, and when turning to the right it is subtracted from it, which gives more variety.

2. Signal Selector is a switch. It performs the function of a tee:) In the event that the number of inputs or outputs is insufficient, use this module.

3. FCV - frequency converter to voltage. Another interesting module that can be used to convert the frequency of sound into voltage, which in turn can be used to control the synthesizer blocks. If you connect a microphone amplifier to its input, and the output of this device to a VCO, then you can easily control the sound-height row of the synthesizer with your voice, flute, or some other external musical instrument.

4. Lost modules - it can be any variety of modules that do not yet exist in nature :) Everything depends only on your creative invention :) For example, it can be a highly sensitive encephalograph, which allows you to take all sorts of alpha, veta, gamma from your brain or bioelectric activity with the muscles of the body and convert it into a control voltage, which, in my opinion, will give interesting results when studying the feedback man-machine, machine-man. Ultimately, it will provide an opportunity to integrate more deeply into the world of "silicone monsters" :) Or, for example, the Termenvox, which is rather scanty in sound, can be easily integrated into a synthesizer, which in turn will allow you to use additional features to control this synthesizer. Well, etc. In essence, such a studio synthesizer is an electronic-acoustic laboratory in which you can explore and use your creative ideas ...

Now we come to the most interesting part - switching the blocks between themselves.

The more degrees of freedom in commutation, the more freedom in the practice of sound extraction we have. Do not be afraid to switch the blocks together. The only thing you need to remember is not to combine the two outputs together. For switching in the modules on the front panel, it is best to bring out the jacks for microjacks. They are more compact. Who does not like the "beard" of the wires, they can make yourself a type-setting field. The x-axis outputs control outputs, the y-axis controlled inputs, or you can make an electronic analog switch and the N / M keyboard field. On average, about 40x40 buttons, depending on the complexity and number of modules in an analog studio synthesizer. That's why I say that the “beard” of wires will probably still be better :) Simple and reliable.

Typically, studio analog synthesizers use from 8 to 16-32 VCO generators, 4-16 VCF and as many VCA. I would put the LFO on each managed module one at a time, i.e. VCO + LFO, VCF + LFO, VCA + LFO. What is there a trifle there:) I would do the same with the ADSR, i.e., in simple terms, there are two control units for one controlled unit. It is very convenient to place all these modules in a shallow drawer, cabinet in an upright position of the Mini-Rack standard, or who can make a rack for them on their own, or purchase one and fill it with mini-Rekov modules.

It turns out very beautiful, especially if the panels are painted in matt black. Pens best to pick one company and one model. You can use handles of different diameters. For example, I really liked the gray plastic knobs that are commonly used in professional mixers. Yes, and they are relatively inexpensive - 3 rubles thing (in bulk). Potentiometers are best used rotary, not strip. Dust gets very often dusty, so they deteriorate quickly, and rotary potentiometers are much more compact, so the module panel can also be quite compact. If someone worked at the big console of the mixer, they probably understand me. Climbing on a very large perimeter is very tiring:) It is also a good idea to display LED bulbs on the control module panel. Then immediately you can visually determine which unit is currently running.
Constructive studio synthesizer can be very diverse. The main thing is to stick to the modular design. This will increase the device to infinity :)

by Ambush 04/16/2008

Well, now personally from me

Emulators

Not many large studio modular analog synthesizers are available. But if you really want, you can understand the principle using software emulation.

VSTi Moog Modular - www.arturia.com/evolution/en/products/moogmodularv/intro.html
Emulators of real-life synthesizers. To study can be difficult. The structure is rigid (the number of modules does not change).

There are other synths of varying degrees of modularity.

Arturia

ARP

SynthMaker www.synthmaker.co.uk
Environment to create your own synthesizers and its interface.

Simulator synthesizer emulating analog synthesis NordModular :)

VOID Modular System - www.psoft.co.jp/en/product/void

VSTi, which I would recommend for studying modular synthesis. You can assemble the synthesizer yourself from an arbitrary number of modules.