Synths come in many different forms, shapes and sizes. I’m going to cover a few of them here, but many synths are combinations of several types.

Modular vs. All-In-One
There are many different components that make up a synth.  Some of them create sounds, some of them modify sounds, and some of them control how signals are routed around.  Don’t worry, we’ll get more into the details of these components in later lessons.

In a modular synthesizer, these components are all separate.  They are usually mounted in a rack, and they can be physically moved around into whatever layout you want.  There is no default signal routing;  you must connect each module you want to use to other modules with patch cables.  While there are some general guidelines for patching modules to getting certain sounds, there are no rules.  Some of the craziest sounds come from patching things at random or in ways that don’t initially make sense.  Many modulars don’t even have a keyboard attached to them.

All-In-One synths have all the components to make a certain range of sound built inside their case.  This includes analog units where “patching” is done with switches and knobs, as well as modern day “Casio Keyboard” type synths where all you have to do is pick your favorite preset.

This site is mostly going to focus on modular synthesizers.  They are the most flexible, they are great for learning because you can see exactly where your signal is going, and frankly they’re a lot of fun.

Analog vs. Digital
Analog signals are represented by continuously-variable voltage levels in analog circuits.  By “continuously variable” I mean that for every increment in signal level, there can be one in between.  The number of levels that can be represented by an analog signal approaches infinity.

When synthesizers were first created, analog was the only game in town.  Signals were generated and modified directly by electronic circuits.  If you wanted do do something new with your signal, you had to change the circuits.

Eventually digital arrived on the scene.  Digital sounds are represented by a series of numbers, each of which corresponds to a discrete signal level.  When these numbers are converted to an analog signal, you get your sound.  Because digital systems can only store and process a finite amount of numbers, they can’t represent every possible signal level.  You can, however, use enough numbers that it’s difficult for the human ear to tell the difference between a digital signal and the analog signal it’s trying to mimic.

Sounds in the digital world can be programmed without having to change any circuitry.  This allowed musicians to get a whole new range of sounds that weren’t previously possible.

Digital has quite a few advantages over analog; digital synths are cheaper, they stay in tune, and sounds can be reproduced identically time after time.  Many people, however prefer the sound of analog synths.

Some synthesizers are hybrids of the two technologies.  The signal path in these units is all analog, but the control circuitry is digital, giving you the advantages of both worlds.

The lessons on this site are going to focus mostly on analog synthesizers.

Monophonic vs. Polyphonic
How many notes can the synth play at once?  Monosynths can only play one note at a time, while polysynths can play 2 or more.

What happens when you press more than one key on a monophonic synthesizer?  Different synths have different ways of dealing with the situation.  Some use low-note priority, which means they output the lowest note being played.  Some use high-note priority, which outputs the highest note being played.  Some get a little fancier and use last-note priority, which means they output the most recent note played, regardless of whether it is hightest, lowest, or somewhere in the middle.

It takes a separate voice chain for each note, which presents some challenges when designing a polyphonic synth.  Each voice chain means an extra bunch of electronics.  All the oscillators must be in tune with each other.  There must be some kind of logic that assigns each note played to a specific voice chain.  It is for these reasons most analog synths were monosynths.  As digital technology progressed it became easier to implement polyphony, first with digitally-tuned oscillators and digital voice-assigners, then with the sounds themselves being generated digitally.

Hardware vs. Software
Hardware synthesizers are actual, physical electronic devices.  All the generation and processing of signals is done in the circuitry of the synth.  Hardware synths can be analog or digital, depending on their circuitry.

Software synths (soft-synths) exist entirely inside a computer.  You load a program and suddenly you have a synthesizer on your screen that you can use.  Soft-synths are often designed to mimic a specific hardware synth as accurately as possible.  They can even emulate analogue synths, even though they themselves are always digital.

The line between hardware and software synth is often blurred.  Some units are basically a specialized computer inside of a box with a keyboard and software-assignable controls.