1.- PRESENTATION

Some customers who brought us musical instruments for repair or overhaul, asked us about the manufacture of analogue modules for modular synthesizers, since what is currently on the market, or are not very good, or are mostly digital modules, with very little in analogue. We have made some consultations and we have decided to open another department dedicated solely and exclusively to music synthesis. It will be called ATM-Music. We have dusted off the old analogue module schematics that we used in the 80s, we have taken out the drawers of old components that we had in storage and we are going to dedicate ourselves to making modules for modular synthesizers based on the Eurorack standard system. We’ll start with some introductory theory on music synthesis and synthesizers and their modules.

2. INTRODUCTION TO SOUND SYNTHESIS.

Sound synthesis is the process of creating artificial sounds by manipulating electrical or digital signals that represent sound waves. This technique is used in the creation of music, sound effects for films, games and other media, as well as in the research and design of musical instruments.
Sound synthesis has developed over more than a century, and numerous methods and techniques have been created to generate and manipulate sounds. The first electronic synthesisers emerged in the 1920s, based on the generation of electrical signals of different frequencies and waveforms. One of the first synthesizers was the Telharmonium, developed by Thaddeus Cahill in 1897.
Over the following decades, various types of synthesizers were developed, such as vacuum tube synthesizers, transistor synthesizers, digital synthesizers and modular synthesizers. Each type of synthesiser uses different components and techniques to create sounds.

3. DIFFERENT TYPES OF SOUND SYNTHESIS.

Additive synthesis: Additive synthesis is a method of sound synthesis in which sounds are created by adding multiple sine waves of different frequencies and amplitudes. This technique is based on the principle that any sound can be broken down into a set of simpler sine waves, known as partials, which are integer multiples of a fundamental frequency.
Additive synthesis was one of the first methods used to synthesise sounds electronically and became popular in the mid-20th century with the invention of the analogue synthesiser. Additive synthesisers typically have a set of oscillators that generate multiple sine waves and an amplitude and frequency control system for each of them. These oscillators can be controlled by a keyboard, sequencer or by external control signals.
The advantage of additive synthesis is that it allows the creation of complex, harmonically rich sounds. By combining different partials with different amplitudes and frequencies, it is possible to create sounds with a wide variety of textures and timbres. However, this technique also has some limitations, such as the complexity of adjusting each partial to achieve the desired sound and the difficulty of creating sounds that do not resemble familiar acoustic instruments.
Despite these limitations, additive synthesis remains a popular method in music production, especially in electronic music. Today, digital synthesisers and additive synthesis software offer greater flexibility and control over the synthesis process, allowing musicians and producers to create more complex and advanced sounds.

Subtractive synthesis: Subtractive synthesis is a sound synthesis method based on the manipulation of a complex, harmonically rich sound to obtain simpler sounds with fewer harmonics. In subtractive synthesis, a sound generated by an oscillator or an external sound source is taken as a starting point and its harmonic content is reduced by filtering.
The sound generated by the oscillator or sound source is sent to a filter that allows only a part of the frequency spectrum to pass through, while the rest is attenuated or eliminated. The filters used in subtractive synthesis can be of different types, such as low pass, high pass, band pass, among others. Each of these filter types allows only a part of the frequency spectrum to pass through, which produces different effects in the resulting sound.
Once the sound is filtered, it is sent to an amplifier that controls the amplitude of the sound, i.e. its volume. In this way, the duration and level of the resulting sounds can be controlled.
In addition to the sound source, filter and amplifier, subtractive synthesizers often have other modules, such as ADSR envelope generators to control how the sound is started, sustained and turned off, and low frequency oscillators (LFOs) to generate effects such as vibrato, tremolo and amplitude modulation.
Subtractive synthesis is one of the most popular and widely used methods in music production, and is present in most analog and digital synthesizers. Its popularity is largely due to its ability to produce a wide variety of sounds, from simple, clean sounds to more complex, harmonically rich sounds.

Modulation synthesis: Modulation synthesis is a sound synthesis method that is based on modulating the frequency, amplitude or phase of a carrier wave using a modulating wave. In modulation synthesis, the carrier wave is generated by an oscillator, while the modulating wave is generated by another oscillator or external sound source.

Frequency modulation (FM) synthesis: Frequency modulation (FM) synthesis is a method of sound synthesis in which a modulating waveform is used to vary the frequency of a carrier wave. FM is commonly used in digital synthesizers and was popularized by the Yamaha DX7 synthesizer in the 1980s.
In FM synthesis, the carrier wave is an oscillator that produces a sine wave and the modulating wave is another oscillator that is used to vary the frequency of the carrier wave. The result is a complex wave that contains a series of harmonics that add up to generate a rich, complex sound.
FM synthesis is based on the mathematical theory of Bessel functions, which describes how sine waves combine to produce a complex wave. By modulating the frequency of the carrier wave with a modulating wave, a series of harmonics are created that add up to generate a complex signal with a large number of harmonics and a bright, metallic tone.
FM synthesis allows a wide variety of sounds to be created, from bright, percussive sounds to soft, melodic sounds. In addition, FM synthesis is very efficient in generating percussive and bass sounds, as well as creating complex sound effects. It is also used for the synthesis of acoustic instrument sounds, such as pianos, guitars and strings.
FM synthesis is very flexible and can be used to create sounds of any type. However, it can be difficult to program because of the mathematical complexity underlying FM synthesis. For this reason, many FM synthesizers include a library of predefined sounds that users can select and modify.