What is a synthesizer?

A synthesizer is a electronic machine or a software able to produce a wide variety of sounds, ranging from real world instruments to new original sounds, a synthesizer is often able to produce also sound effects.

A synthesizer is generally composed by a variable number of devices (hardware or software) each one interconnected with the others, these interconnections can be combined in several ways and each device can shape the sound in its own way so that the final sound can be anything, like pure noise or a lovely warm pad. The synthesizers allow musicians to create sounds and instruments that are impossible to find in the real world.

Synthesizers can be grouped into the following types: “analog”, “digital”, “hybrid”.

Oscillators

The oscillator is the device responsible of the basic sound creation, an oscillator (also called tone generator) outputs a pulsing electrical signal to create a “waveform”. The frequency of the pulses determines the pitch of the sound, for example a waveform with a pulse frequency of 440 (pulses per second) would create an “A” note.

An oscillator is generally able to generate some classic waveforms like the “sawtooth wave”, “triangle wave” and “square wave”, these waveforms determine the sound timbre of a sound, but a modern oscillator can generate many other waveforms allowing musicians (and technicians) to shape the sounds they need. Most synthesizers are also able to generate completely random waveforms called noise wave.

 

Filters

A filter is a device used to selectively increase or decrease specific frequency regions, effectively smoothing out the edges of the original waveforms. Filters are also used to cut out some specific frequency regions.

 

 

Amplifier

An amplifier is a device able to control the volume of a sound, the amplifier can raise or lower the height of a waveform, changing the final waveform volume. An amplifier is also seen on synthesizers as “VCA”, voltage controlled amplifier, and it can be applied to other synthesizer elements to layer oscillators and filter volumes.

 

Envelope

Natural sounds don’t normally switch simply on and off.  Sounds are hardly ever “static” and change their character through time. A real life sound has a fade-in and fade-out period. To take an example, a drum hit begins very sharply as the drumstick hits the skin and also fades away quite fast.

The sound volume of a note on the piano will also rise rather quickly, but will dampen much more slowly.  Many sounds also change their pitch between the onset and the fade-out, like how the pitch of a train whistle drops as the train passes by. This behavior is called the “envelope” of the sound.

To simulate this effect on a synthesizer, we must be able to control the oscillator, the filter and the amplifier in a much more detailed way than just a basic on/off function. We want to be able to control the “envelope” for each synthesizer circuit. The envelope of the oscillator controls how the pitch changes through the duration of the sound and the envelope of the amplifier controls how the volume changes over time. The filter has also its own envelope, which controls the changes in the “brilliance” or “dullness” of the sound.

The simplest synthesizers envelopes have four stages. This means that they control four different parts of the envelope. These different parts of the envelope curve are termed “ADSR”:

• Attack (the initial onset of the sound)
• Decay (the first fading of the sound)
• Sustain (the level at which the sound is held as long as the key is depressed)
• Release (the fade out of the sound)

All these different stages of the envelope can be set individually.  The envelope generators of some synthesizers have many envelope stages, which makes it possible to create some very complex envelopes and interesting sounds.

 

Low Frequency Oscillator (LFO, Modulation)

Most synthesizers have a wheel controller to the left of the keyboard labeled, “Modulation”.  This enables the performer to mix in a very slow oscillation to a sound, creating “vibrato” or “filter sweep” effects.

 

Voices

The first synthesizers were all “monophonic” synthesizers. If you wanted to play chords, you would have to buy more than one synthesizer – one for each tone.

By adding more oscillators, filters, and amplifiers in the instrument, the synthesizer can play more than one sound at once.  A synthesizer with eight voices can play eight tones at the same time.  This may seem enough, but a modern synthesizer is usually equipped with 32, 64, or even 128 voices. One could ask, why anybody would need an instrument which can play 64 voices at once – nobody in the right mind would want to play (and listen to) huge 64-note chords.

Well, first of all, voices can be stacked on top of each other to create a more complex sound. A single key depression could for instance play a piano voice, a string voice and a choir voice at the same time. It’s easy to see that the available voices are quickly gobbled up when playing with such a complex voice stack. But the main reason is the ability to let the synthesizer play more than one part at once in a musical piece.

Nearly all modern synthesizers are “multi-timbral” instruments, meaning that the synthesizer can play several different sounds at once. If the synthesizer is connected to a computer, it can for instance play drums, strings, brass, bass and guitar parts – all at once, like a big one-man-band.

 

Waveforms and Samples

Some hybrid synthesizer/samplers also contain banks of audio samples or “waveforms”, which are digital audio sound clips that may be used instead of a simple oscillator tone.  The synthesizer modules (filters, envelopes, LFOs, etc.) may then be applied to create an infinite variety of sounds.  Samplers can also record any natural sound with an attached microphone, which may then be converted and used as a waveform/sample.  Wavesample voices and oscillator voices can also be combined to create amazing, complex sounds.

 

Welcome to the synthesizers world!

 

External resources