UA3MQJ September 13, 2014 at 22:20

Modular Analog Synthesizers

Going through old documents, I found an article with which I began to have a passion for analog modular sound synthesis. I want to inspire you too.

The article, unfortunately, has been preserved only locally, and the original does not open. Thanks to the author - Unknown Ambush . The text is slightly adjusted and revised by me.

Electronic musical 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

By subtractive we mean synthesizers with a rich spectral composition of the initial generators (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 voltage-controlled amplifiers and time function generators.

Additive (harmonic synthesis)

Harmonic synthesis is the most accurate and subtle way to synthesize sound. This is carried out by the method of summing sinusoidal functions, where each function can arbitrarily change the amplitude and frequency. To build such a synthesizer, the Nth number of generators of such functions is necessary (from about 40 and above, on average, about 256 generators).

FM synthesis

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

Any original and original synthesis methods

Methods that, due to some circumstances, could not be further applied. There are so many of these methods that it probably makes no 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 Mug, although devices of this type existed long before its discovery. These devices were called analog electronic computers. Robert Mug just systematized and adapted this type of analog machine 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 one-voice. The keyboard is a source of calibrated control voltage and control pulses ("start", "strobe", in English GATE ). A short “start” control pulse appears when a key is pressed. 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 a key. Such keyboards are called dynamic and are very expensive, but allow the musician to show all his performing skills.

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

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

Analog sequencers- These are software devices that allow the output to receive a control voltage multiplexed by an analog device from potentiometers. The position of the angle of rotation of the potentiometer knob determines the control voltage. Sequencers can change not only the frequency (scanning speed of the potentiometer matrices), but also the duty cycle (ratio of pause to duration). 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 size:) 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 store code from the scanning matrix of the keyboard into memory. They can have a huge amount of memory and memorize the score, both polyphonic and single-voice musical works. As in analog sequencers, you can edit the tempo there and arbitrarily change the duration and frequency of the notes.

4. Joystick is a joystick. Typically, these are two potentiometers located 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 motion to control two parameters at once. There is also a wheel called Pitch Bend. Serves to receive "braces".

Generator Modules

1. VCO is a voltage controlled oscillator, 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 shapes are used for this. For example, a rectangular voltage may be able to change the duty cycle of the pulses (the ratio of pause to 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. 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 range of low frequencies - 0.01-100 Hz. These devices, in turn, can also be voltage-controlled and modulated by the same generator as he himself. But, as a rule, such a generator is triggered by a “strobe” or “start” signal, which correlates with the time functions of the keyboard, sequencer and other devices. As an LFO, you can sometimes use ADSR, on which you can build the necessary function in advance.

4. ADSR is a function envelope generator.
A - ( attack ) - initial phase, rise
D - ( decay ) - phase of transition of sound to steady state
S - ( sustain ) - phase of “support”
R - ( release ) - after sound
It is used to control VCO, VCF, VCA, as well as LFO units. There are ADSR blocks with a large number of elements approximating the function - from 4 to 8. Sometimes these modules perform with a voltage level of elements, i.e. attack time can be set by voltage from a non-koi external generator of time functions, for example, 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 high-altitude row of the keyboard. ADSR is typically triggered by a “gate” signal from a 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.

http://www.youtube.com/watch?v=jERCSkrDd0U

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

Voltage Controlled Modules

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

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

2. VCA is a voltage controlled amplifier. Used to control the function of the amplitude-time characteristics. As a rule, it works together with the 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 upscale and have a very low noise figure.

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

Support Modules

1. Mixer is a mixer. It is necessary for mixing the Nth amount of sound or control signals. As a rule, these are small mixers from 4 to 8 channels. There are mixers that perform the functions of adding and subtracting at the same time. In the middle position of the potentiometer, the output voltage of the channel is 0. When turning from 0 to the left, the signal is added to the other channel, and when turned to the right, it is subtracted from it, which gives more variety.

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

3. FCV- frequency to voltage converter. Another interesting module that can be used to convert the frequency of sound to voltage, which in turn can be used to control synthesizer blocks. If you connect a microphone amplifier to its input, and the output of this device to VCO, you can easily control the high-altitude range of the synthesizer using a 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:) It all depends on your creative invention:) For example, it can be a highly sensitive encephalograph that allows you to take all kinds of alpha, veta, gamma from your brain or bioelectric activity from 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. In the end, it will provide an opportunity to integrate more deeply into the world of "silicone monsters":) Or, for example, the Theremin quite meager in sounding can be very easily integrated into the synthesizer, which in turn will allow you to use additional features to control this synthesizer. Well, etc.

Now we turn to the most interesting thing - switching blocks between each other.

The more degrees of freedom in switching, the more freedom in the practice of sound production we have. No need to be afraid to switch blocks between each other. The only thing to remember is not to combine the two outputs together. For switching in modules on the front panel, it is best to output jacks for microjacks. They are more compact. Whoever doesn’t like the “beard” of wires, they can make themselves a composing field. The X-axis displays the control outputs, the Y-axis controls the inputs, or you can make an electronic analog switch and a keyboard field N / M. On average, there are 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 the wires, probably, will still be better :) Simple and reliable.

Typically, studio analog synthesizers use 8 to 16-32 VCO, 4-16 VCF, and the same VCA. I would put LFO on each managed module one at a time, i.e. VCO + LFO, VCF + LFO, VCA + LFO. What are the little things there :) I would have done the same with ADSR, i.e., more simply put, there are two control blocks per managed block. All these modules are very convenient to place in some shallow drawer, a cabinet in the vertical position of the Mini-Rack standard or, who can independently make a rack, or purchase it and fill it with mini-rack modules.

It turns out very beautifully, especially if the panels are painted in matt black. Pens are best chosen by one company and one model. Handles of different diameters can be used. For example, I really liked the gray plastic knobs that are commonly used in professional mixers. Yes, and they are relatively inexpensive - 3 rubles a piece (in bulk). Potentiometers are best used rotary rather than strip. Dust very often gets in stripes, so they quickly deteriorate, and rotary potentiometers are much more compact, so the module socket can also be quite compact. If anyone worked behind a large mixer console, they will probably understand me. Climbing around a very large perimeter is very tiring :) It is also nice to display LED bulbs on the control module panel.
The design of a studio synthesizer can be the most diverse. The main thing is to adhere to the modular design. This will allow to 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 to, you can understand the principle using software emulation.

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

There are other syntheses of varying degrees of modularity

Arturia

ARP

SynthMaker www.synthmaker.co.uk An
environment for creating your own synthesizers and its interface.

NordModular analog synthesizer emulator emulator :)

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

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

ALSA modular Synth - alsamodular.sourceforge.net

Pure Data - PD Community Site - puredata.info

Audiomulch - www.audiomulch.com

And many others: lesitedeburnie.free.fr/lalistedeburnie1-en.html#synthesizers