Synthesizer Part 2 (Modules)

synthesizer modules analog  - AEDM Synthesizer 1203x800 - Synthesizer Part 2 (Modules)

Synthesizer modules

What does a synthesizer consist of? It consists of different modules and with them it is possible to create sounds. Moreover one can change and steer the pitch, volume and timbre. A power source is definitely needed, which is also used for the steering of the elements.
Electronic power has amperage and voltage. Beginning of the 1960’s Robert A. Moog decided to focus on voltage to be able to manipulate automatically (so without turning a button or something similar). That’s how he was able to influence the pitch or to create other sounds.
The synthesizer modules were usually controlled by a low voltage triggered by the keyboard, which meant that the changes could already be programmed beforehand.
Let’s get back to the initial question of the synthesizer modules of an analogue synthesizer. It includes three main components:

– Voltage Controlled Oscillator (VCO); ( in digital synthesizer you can find the Controlled Oscillator (DCO) )
– Voltage Controlled Filter (VCF)
– Voltage Controlled Amplifier (VCA)

Furthermore there are additional oscillators, like the LFO (low frequency oscillator) and steering elements („Envelope-Generator”), sequencer, patch cable (which were needed for the connection of different modules), controller for adjustments, a speaker, a so called “rack” (in which everything was stowed) and a keyboard (especially for the Moog-synthesizer).

The oscillators

With an oscillator regular vibrations are generated, which can take different curve shapes. The basic function of an oscillator is that a capacitor is charged slowly until a certain reference value. Then by using a switch (e.g. via a keyboard), it gets short-circuited, so discharged.
By that the voltage in the capacitor is under the reference value and the whole thing can repeat itself.

If you would create a schematic drawing from the up and down of the voltage, it would look like the shape of saw tooth. It can be used for string, accordion and brass syntheses. Besides the saw tooth form there are equally important ones, the square wave form. You can also speak of a pulse wave. She is created by a circuit, which occurs when the saw tooth is over or under the steering voltage. When the periods, in which you switch it on or off, of the same length, it would look like a regular rectangle. If they don’t have the same length you speak of a contrasting pulse width. The rectangular waveform includes only these sounds, which for example can be used for clarinets- or flute-like sounds or as baseline in electronic genres. Besides saw tooth and rectangular wave, the triangular wave (includes only a few overtones), the sine waves (only one base tone, no overtones), as well as Spaced Saw and Moog Saw are common waveforms of analogue oscillators.

Moreover there is another waveform, which does not repeat itself regularly: the murmur. Above all it is important for percussive sounds. The murmur is created by a module, which is not regulated by a voltage. This component is a murmur generator. With it you can differentiate so called white murmur (regular high and low frequencies), colored murmur (irregular high and low frequencies) and pink murmur (low frequencies are the majority). With the murmur generator you can create not only noises or specific effects, but often also unusual sounds. The oscillators are mostly coupled to a switch, with which you can choose the wave form. With a moog synthesizer you can even change from one mode of vibration to the other.

The filter

The second important component of a synthesizer is the filter. The filter is voltage-controlled and you use it to the smooth the sound of certain overtone vibrational forms. Besides there are also fixed filter, so filter which are not steered by voltage. With them, the parameters are set by hand. The lowpass filter is the most used filter. The upper vibration range is cut, while the lower frequencies are retained. The capping point is called the cropping frequency, capping frequency, cutoff frequency or cutoff frequency. The situation is different with the high-pass filter; it eliminates the lower vibration range, while the upper frequencies persist. If you combine low and highpass filters, so if you put them in series, you get a bandpass filter, which only lets through the characteristic frequency. The more the other frequencies are away from it, the less the number of frequencies which can occur. If the switching of high and low pass filters occurs in parallel, a band-stop filter is created. The bandpass filter also has a counterpart. It is the notch filter, also called notch filter and bandstop filter. All areas suppressed by the bandpass filter are allowed to pass through; instead, the characteristic frequency is hidden with those areas that are in its vicinity. The filters can also be brought to resonate. If this resonance effect is high enough, the filters themselves produce vibrations like an oscillator. Since the built-in Moog synthesizer filter is able to do this in a special way, it is also called the Moog filter. The silence of the signal, that is its distance from the characteristic frequency, can be slower or faster. The frequency drops steeply or not so steeply. The term slope steepness describes this degree. It is expressed in dB / oct, which is decibels per octave. The third main module of a synthesizer is the amplifier. It is voltage-controlled and its function is to influence the volume level, to make a sound audible or silenced at the desired level. When a button is pressed on a synthesizer, a sound is heard. When it is released, then it stops. The amplifier can also be used for other tasks, such as control voltages for particularly complex sound changes.


An analogue synthesizer contains next to the three main synthsizer modules oscillator, filter and amplifier as an additional element an LFO (Low Frequency Oscillator). It is used to change the voltage-controlled components of the synthesizer modules. By using an LFO, different effects can be achieved, such as vibratos, tremolos or so called wah-wah effects.


Another important module is the envelope generator. Its function is to control the volume, but also the pitch and the filter automatically. First, however, is to clarify what a volume envelope is all about. Generally speaking, this is to be understood as a kind of list of tonal states which are reached in certain periods of time. The most common envelope is the so-called ADSR envelope, which consists of the four parameters attack, decay, sustain and release. The parameter attack determines how much time is needed to reach the maximum value. The parameter decay denotes the time to move from the maximum value to the sustain level. The sustain parameter refers to the duration of the volume of a steady tone after the decay process has finished. The release parameter determines the amount of time needed after the key is released to allow the voltage to drop to zero. A main function of the ADSR generator is to control the volume through the amplifier. But also by the use of envelopes with the filter sound variations can be created. The Envelope Generator is triggered in most cases via the keyboard of the synthesizer. By pressing a key, so to speak, the start signal for the predetermined envelope curve is given.

The sequencers

Sequencers are control units. They can be an electronic device, so hardware or software. They are available in analog and digital form. Analog versions – they are hardly used today – produce automatic voltage sequences. Digital sequencers also influence the devices. This is not done by control voltages, but by digital signals. Even Don Buchla and Robert A. Moog used sequencers as synthesizer modules. At first was the analog step sequencer. They proceeded step by step. A multi-layered sound sequence was subdivided into steps, which were then programmed one after the other with their associated features and characteristics, such as pitch and tone length, and then they were stored. Sequencers that worked in this way were kind of storage containers for certain sound patterns. In the beginning, however, the storage capacity was limited with the technology of that time. A maximum of 64 steps were possible, which had to be programmed individually. Accordingly, analog sequencers were quite large and bulky.

The next part

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6) Brockhaus encyclopedia
7) Audio Encyclopedia by Andreas Friesecke