Sound Synthesis 101: Synth Basics

For those of you just getting started with your very first synth, this is for you! Rather than going into textbook style depth on the history, the physics and technicalities (and this stuff gets extremely technical), this series will deliver practical, easily assimilated explanations that you can put to immediate use. So fire up your synth and let’s get to tinkering!

Weapon: The Synthesizer

The synthesizer is the most basic tool in every electronic producer’s kit. It is unique in the sense that the sound it creates is 100% artificial. Because of this, they can very easily sound lifeless, and utterly boring. There are many ways to breathe life and interest into these sterile noises, but before ANYTHING – before any type of audio mangling, effecting or sequencing, you begin with a tone.

*Beep*

Synthesizers, or synths, come in all shapes and sizes, put together or in pieces, with more or less options, but the fundamental structure of a synthesizer is linear- a sound is created and passes through various modules until it is amplified and played through a speaker. Different synth types use different processes to create sounds, but the most common type of synth uses a process called subtractive synthesis. This starts with a tone and allows the user to sculpt the tone with various modules.

The Basic Synth Modules

The Oscillator

This is the “noise maker.” There are a few different types, but essentially they behave the same. They produce sounds by generating or playing back an artificial waveform, of which there are several types. Each oscillator produces its own tone. Many synths have more than one, and the big ones (like Dave Smith Instruments’ Prophet line) can have as many as twelve! The most common waveforms include:

• Sine – one fundamental tone; no overtones. Smooth and warm sounding.
• Triangle – a little more aggressive than sines, less aggressive than saws. Imagine a sine wave with a little more bite.
• Sawtooth (Saw) – rich with overtones, which makes it excellent for filtering. Sharp sounding.
• Square – hollow sounding with rich overtones, but not as rich as a saw.
• Pulse – an irregular variation of the square wave.
• Noise – it’s exactly what it sounds like. Static noise. A random, haphazard waveform.

The Filter

This module does exactly what you would imagine. It filters out frequencies created by the oscillator, just like your Brita filters out unwanted stuff from your tap water. There are many filter types, but the most basic types are:

• Low Pass – removes frequencies above a threshold
• High Pass – removes frequencies below a threshold
• Band Pass – removes frequencies above and below a specified range

Additional components of a filter are slope, which defines the sharpness of the filter cutoff, and Resonance, which increases the level of the cutoff frequency of the filter.

The Modulators

The word modulate means to change. These modules are a little bit more abstract than the two listed above because they affect the operation of other modules There are many different types of modulators available in the world of sound synthesis, but the most common ones are envelopes and LFO’s.

Envelopes

This module determines the length and quality of an aspect of the oscillator. Actually, you hear envelopes all day long. Think about a sound. Any sound. Got it? Great. Now think about the changes the sound goes through in terms of volume from when it begins to when it ends. That is an envelope. More precisely, that is an amplitude envelope. An envelope can be split into four distinct stages: Attack, Decay, Sustain, and Release – or ADSR for short (I love “aha” moments, don’t you?).

• Attack – This is how quickly the sound rises to its maximum amplitude. The shorter the attack, the faster it gets loud. Drums have a very fast attack.
• Decay – This is how long it takes for the attack volume to drop. The longer the decay, the slower the volume will drop after it reaches it’s max volume.
• Sustain – This is the volume a sound will stay at for as long as it will continue to sound. Guitar strings technically have no sustain, as the sound will continue to decay until it is silenced. Violins, however, can maintain a steady vibration for as long as the bow is drawn across its strings.
• Release – This is the time it takes for a sound to fade into silence when it is no longer sustained. It could be thought of as a second decay stage.

Envelopes can be applied to many aspects of a sound, but most commonly they are applied to the filter and pitch. Envelopes can also be applied positively and negatively – that is they can pull the pitch or filter down and let it come up or pull it up and let it come back down.

LFOs

Basically, that’s exactly what happens with an LFO. The acronym stands for Low Frequency Oscillator. This does not mean “bass.” The LFO fluctuates at such a low frequency, it cannot be heard. But what it can do is affect, or modulate, other aspects of the sound being crafted. When you put an LFO on volume, you get a tremolo effect of the volume going up and down at the speed of the LFO. When applied to pitch, you get a vibrato – the note heard will fluctuate over time to the degree that the LFO is applied.

Since an LFO is an oscillator, you can also assign any of the oscillator types listed above – provided they are available on your synth.

Some synths have LFOs with such a wide range, they can actually cross the threshold for human hearing. Essentially, they become another regular oscillator. The difference is it can alter the parameters of an existing oscillator to produce some really out there types of sounds. Apply an audible oscillator to modulate the pitch of another audible oscillator and you move into a whole new type of synthesis, called Frequency Modulation, or FM synthesis – and that is a whole other story.

Conclusion

There are many other tools and modules for use on a synthesizer, but to cover everything would result in a book. I will go over more in future articles. The modules covered provide the foundation for basic sound synthesis and synth operation.

Are there modules or functions on your synth that you would like to see covered? Drop me a line on the contact page and I’ll put it in the next entry of this series.

Now bust out that synth and experiment!

-Chris Lazaga
Audiomunk