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Yamaha Motif synthesizer keyboard


Synthesizers are the most modest musical instruments you can imagine. They look like small and rather mundane electronic pianos, but they're actually much more than that. If you can play a synthesizer, you can play not just any instrument in the orchestra but any instrument you could possibly imagine. Synthesizers have radically changed popular music since they were first widely used in the early 1970s; hardly a pop record is made these days without featuring an electronic keyboard of some kind. How do these amazing gadgets work? Let's take a closer look!

Photo: Two in one: There are two completely separate electronic synthesizer keyboards stacked together here. The top one is a 61-key Yamaha Motif ES 6. Unlike a piano, the sounds from these keyboards can be changed in all kinds of ways using the switches and knobs at the top. A small digital display (green, center) helps you program the machine. Photo by Brian T. Glunt courtesy of US Navy and Wikimedia Commons.

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  1. What is a synthesizer?
  2. Sound is energy in motion
  3. What makes one instrument sound different from another?
  4. How synthesizers work
  5. Additive and subtractive synthesizers
  6. Analog and digital synthesizers
  7. How to make your own synthesizer using Audacity
  8. Who invented synthesizers?
  9. Find out more

What is a synthesizer?

Yamaha DX-9 synthesizer

Photo: The Yamaha DX-9 synthesizer, popular in the 1980s, is much more than just an electronic piano. Other famous makes of synthesizers include Moog, Roland, Korg, and Casio.

A synthesizer (sometimes spelled "synthesiser") is an electronic keyboard that can generate or copy virtually any kind of sound, making it able to mimic the sound of a traditional instrument, such as a violin or piano, or create brand new, undreamed of sounds—like the crunch of footsteps on the surface of Mars or the noise blood cells make when they tumble through our veins.

"Synthesize" means to make something new, often by putting it together from existing pieces. So we can think of a synthesizer as an electronic gadget that makes new sounds by piecing together "old" ones. To understand how it does that, we need to know more about sound and how different instruments produce it in different ways.

Sound is energy in motion

Suppose you're sitting in a room with a friend who has a large drum that she bangs from time to time with a large stick so, every so often, you hear a drum beat. What sort of science is going on here? Playing and hearing the drum actually involves a series of steps in which energy is converted from one form to another.

A marching navy drummer hits a drum with his sticks

Photo: A marching drummer is firing sound energy off in all directions. Photo of drummers from from the Royal Australian Navy by William R. Goodwin courtesy of US Navy.

When your friend lifts her drum-stick, she gives her arm (and the stick) potential energy (the ability to do something). When she lowers her arm, moving it back toward the drum skin at some speed, it has kinetic energy (the energy something has because it's moving). As the drum stick contacts the taut drum skin, the skin soaks up most of the energy and starts to vibrate. In other words, it has the kinetic energy now. As the skin vibrates, it pushes the air molecules that are in contact with it. The air molecules vibrate too, with each molecule causing neighboring molecules to start vibrating as well. Before long, all the air molecules in the room are vibrating. Some of them vibrate right next to your ear; others vibrate in your ear canal. Inside your ear, the vibrating air molecules make tiny hairs vibrate. The hairs stimulate nerve cells, which send signals to your brain—and your brain perceives these signals as sounds.

In short, we can think of sounds as waves of energy traveling from something that is moving back and forth (vibrating or oscillating) to our ears. The waves travel by alternately squeezing and stretching the air; if there's no air in the room, they cannot travel at all. That's why you can't hear sounds in space, where there's no air, or traveling in a vacuum. If you could see sound waves moving, you'd see the air squeezing and stretching all over your room like an old-fashioned concertina. In science, the squeezed parts of the air are known as compressions (because the air molecules are pressed together) and the stretched parts are called rarefactions (because the air molecules are thinned out and less dense).

Two key features of a sound wave control what it sounds like to us. The frequency (how many times the wave vibrates in one second) is broadly related to the pitch of the sound we hear. So we hear a high-frequency sound as having a higher pitch. In other words, a choir boy's voice produces a mixture of sound waves of generally higher frequency than an adult man's voice. The amplitude (volume) of a sound is related to the amount of energy that the sound waves carry. When you bang a drum hard, you make more energetic sound waves with more amplitude that you hear as louder sounds.

Read more in our main article about sound.

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What makes one instrument sound different from another?

When two instruments play exactly the same musical note, at roughly the same volume, they can sound completely different. How can that be if they're producing the same sound waves? The answer should be obvious: they're not producing the same sound waves! We can use an oscilloscope (an electronic graph-drawing machine, a bit like a cathode-ray TV, only it shows pictures of what waves look like) to see the difference.

Wave shape

If we play a pure musical note with a tuning fork, the oscilloscope shows an undulating hilly pattern called a sine wave. But if we play the same note with a trumpet, the wave will look more zig-zagged, like the teeth of a saw (it's usually called a saw-tooth wave). If we play the same note again on a flute, we will see triangular waves, while a clarinet, blown hard, playing exactly the same note, might well give us square waves. The shape of the sound waves , which is controlled by how the instrument pumps energy into the world around it—in other words, how it vibrates and makes the air around or inside it vibrate in sympathy—is one of the things that makes instruments sound different from one another.

Shapes of sine waves, square waves, and sawtooth waves compared

Artwork: Sine, square, sawtooth, and triangular waves as they'd appear on the screen of an oscilloscope.

You can hear the difference between sine waves, square waves, and sawtooth waves in this little sound clip. In each case, we're hearing a note with exactly the same frequency (440 Hz):


There are other factors too. An instrument doesn't just produce a single sound wave at a single pitch (frequency). Even if it's playing a steady note, it's making many different sound waves at once: it makes one note (called a fundamental frequency or first harmonic) and lots of higher, related notes called harmonics or overtones. The frequency of each harmonic is a multiple of the fundamental frequency. So, if the fundamental frequency (also called the first harmonic) is 200Hz (which we can think of as simply 1 × 200Hz), the second harmonic is 400Hz (2 × 200Hz), the third is 600Hz (3 × 200Hz), the fourth is 800Hz (4 × 200Hz), and so on. Playing together, the harmonics make a dense, complex sound a bit like a barber's shop choir, with low voices and high voices all singing in tune. The more harmonics there are, the richer the sound.

What does it sound like in practice? In this first clip, you can hear a 200Hz tone, followed by a 400Hz tone, a 600Hz tone, and an 800Hz tone—so, a 200Hz tone and three harmonics, all played separately:

In this second clip, you can hear the same tones progressively added on top of one another. So we start off with just the 200Hz tone for 1 second, then add in 400Hz for another second, then add 600Hz for another second, and finally we have a second of all four tones playing together:

Wave envelope

A third factor that makes instruments different is the way the sound waves they make change in volume (amplitude) over time. Instruments don't make sounds the way lamps make light: it's not "all" or "nothing." If you press a piano key and release it, the sound changes volume gradually over time. First, it rises quickly (or "attacks") to its maximum volume. Next, the sound "decays" to a lower level and stays there or "sustains." Finally, when we let go of the key, the sound "releases" and dies down to silence. In a piano, the attack phase is fairly slow and the sustain phase can be really long as the notes take a long time to die away. But with a flute, the attack phase is quicker and sharper, there is little decay, the sustain continues for as long as the flautist keeps blowing, and the release is also very fast. The changing pattern of sound volume plays a huge part in what makes one instrument sound different from another. We call the pattern of attack, decay, sustain, and release the ADSR envelope shape.

Graph of ADSR sound amplitude envelope

Picture: An ADSR envelope shows how the volume of a musical note changes with time. When a sound plays, it attacks to a maximum volume, decays to a lower level, sustains or holds at that level for a while, then releases back to silence.

There's no rule that all four components of the envelope—attack, decay, sustain, and release—have to be present, all the time. In a percussive sound, such as a drumbeat, you have an almost instant attack, a longer decay (depending on what material you're hitting), and effectively no sustain or release. So the envelope looks more like this:

Graph of ADSR sound amplitude envelope for a drum

Picture: An ADSR envelope for a very simple drum sound. You can make more complex percussive sounds by varying the attack and decay or adding in a bit of sustain and release, if you want to.

If you take several seconds of "white noise" (all frequencies mixed together) and shape the amplitude over and over again with this pattern of instant attack and longer decay, you get something a bit like a snare drum beat:

How synthesizers work

Now we understand the theory of how sound works, and how different instruments produce it in different ways, we know enough to build ourselves a synthesizer. You can probably see already that a machine that can copy the sounds of virtually any other instrument would need to be able to:

That's pretty much what an electronic synthesizer does in a nutshell. It has a number of different voices or oscillators (sound tone generators), each of which can produce waves of different shapes (sine wave, square wave, saw tooth, triangular wave, and so on). It can combine the waves to make complex sounds, and it can vary the way the sounds attack, decay, sustain, and release to make the sounds mimic existing instruments like pianos.

To make a synthesizer sound somewhere between a piano and an organ, you could select a square wave generator (which gives an organ-like sound) and set the ADSR values to be like those of a traditional piano (slowish attack, quickish decay, long sustain and release). Modern synthesizers have "presets" (ready-programmed settings) or "modes" that let you select particular instruments at the flick of a single switch. Of course, you don't have to copy traditional instruments with a synthesizer: you can change the settings to whatever you like—and create all kinds of sounds no-one has ever heard before.

Additive and subtractive synthesizers

In art, there are two ways to make a piece of sculpture. You can take materials you've found in the world around you and stick them together to make something completely new. That would be an example of working in an additive way. Or you can start with something like a big block of stone or wood and chisel it down, slowly reducing it to what you want by stripping bits away. That's working in the opposite—subtractive—way.

The same is true of making sounds with synthesizers. It's perfectly possible to build up a complex sound from simple tones that you add together and shape in various ways, which is more or less the approach I've described above. But it's much more common for real synthesizers to work the other way, through subtractive synthesis. That means you start with a complex sound, filter it to remove harmonics, and envelope shape its volume. In practice, then, a simple subtractive synthesizer makes sound using four independent components:

  1. An oscillator generates the original sound (and you can control it in various ways), which will be a mixture of a fundamental frequency and its harmonics. Most synthesizers have at least a couple of oscillators.
  2. A filter cuts out some of the harmonics (for example, by boosting or cutting all harmonics above a certain frequency).
  3. An amplifier changes the volume of the sound over time, according to ADSR values that you set (as we discussed above).
  4. A second, independent oscillator, known as an LFO (low-frequency oscillator), can be used to vary how the previous three stages work, producing some very interesting effects. For example, if you apply the LFO to the original oscillator, it can make the frequency of the sound it generates wobble about (a vibrato effect) or wobble its volume (tremelo).

Yes, this is all sounds a bit abstract and mathematical. It's easiest to understand what it means in practice by experimenting for yourself; at the bottom of this article you'll find some suggestions for apps you can download that let you play around with your own simple subtractive synthesizer.

Analog and digital synthesizers

The original synthesizers achieved all this using laboratory-style electronic equipment that generated and manipulated actual sound waves. Instruments like this are known as analog synthesizers because they work directly with the sound waves themselves. Many of these synthesizers had lots of separate, sound-creating modules that could be connected together ("patched") in different ways; that's why they were called modular synthesizers.

Old-fashioned modular synthesizer showing patch cords.

Photo: An old-fashioned modular synthesizer. Each distinct area of this box contains a separate sound-altering module that can be "patched" together with other modules using electrical cables and jack plugs. Photo by George P. Macklin published under a Creative Commons (CC BY-SA 2.0) Licence on Wikimedia Commons.

Modern synthesizers do everything digitally, by manipulating numbers with computer chips. Not surprisingly, they're called digital synthesizers. They're essentially computers that have been specially programmed to generate and manipulate sounds. Most synthesizers can be connected up to personal computers, so the computer can be used to store and record the sounds the synthesizer makes or play it automatically. To make this sort of thing easier, computers and synthesizers use a standard way of connecting together known as MIDI (Musical Instrument Digital Interface).

Another kind of digital synthesizer, the sampler, lets you feed in a recorded sound (maybe the noise of a sparrow singing) and then manipulate it in various ways by changing the sound settings. So you can make the sparrow sing more quickly by speeding up the sound, or play the bird-song on your keyboard, so the low notes sound like older, heavier birds and the high notes like younger, smaller, and chirpier ones!

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How to make your own synthesizer using Audacity

Synthesizers sound amazingly abstract when you read about them in articles like this—and there's really no substitute for playing with them yourself. Now you might not be able to afford a multi-thousand dollar synthesizer, but you can download a free sound-editing program called Audacity (for Windows, Linux, and Mac) and experiment with quite a lot of sound-making effects without spending a dime.

The great thing about Audacity is that you can see the shapes of the waves you create and listen to them at the same time. I'd really recommend playing around with basic sounds like this for an hour or two before you move on to using realistic synthesizer apps. This way, you'll get a feel for how the shape of a sound corresponds to what you actually hear, which can be difficult to figure out if you just play with an app.

I'm not going to explain in detail how to use Audacity, because you can use it for many different things (from converting cassette tapes to MP3s to creating brand new imaginary sounds). To learn about synthesizers, what you need to do is experiment with the tabs marked "Generate" (which can produce sound wave tones of different shapes and frequencies, as well as "white noise"—sound spread equally across a wide range of frequencies) and "Effect" (which will shape the envelopes of the tones you've generated or change them in other interesting ways). Here are three quick examples of sounds I've made to give you an idea.

1. Basic harmonics

In my first attempt at synthesizing a sound, I've added together three square waves of 110 Hz (top), 220 Hz (middle), and 440 Hz (bottom). Then I've faded in the sound at the start (giving a slowly rising attack) and faded it out at the end (giving an even more gradual release), so there's no decay or sustain. That gives me these three fish-shaped envelopes, which are added together in the final sound; the three tones play simultaneously, but our ears add them together so we hear a single, fused sound about 0.5 seconds long:

Audacity synthesizer creating three square waves

The result sounds fairly harsh—not something I'd particularly want to listen to:

2. Adding a wah-wah effect

Next, I've taken the same three waves and applied a wah-wah effect, which wobbles the amplitude up and down to resemble a human voice. Notice how this changes the envelopes of the waveforms without changing the frequencies of the sounds. The higher frequency sounds are changed more than the lower frequency sound:

Audacity synthesizer creating three square waves

It sounds much less abrasive and a bit more interesting. With more work, we could get this quite close to a human vowel sound:

3. Adding noise

For my final example, I've reduced the amplitude of the middle tone by about 50 percent (so the peaks in the trace below are about half as high), removed the lowest tone entirely, and replaced it with white noise that attacks and decays in roughly the same time period. What I'm starting to get now is more interesting:

Audacity synthesizer creating three square waves

Here's what it sounds like—more windy and whistle-like, but still recognizably the same note (frequency). The white noise is starting to take us in a different direction; what we have now sounds like some sort of windy blowpipe:

Clearly we could go on doing this forever. We could add any number of sounds, change their frequencies, durations, wave shapes, or envelopes, and refine each component sound in many different ways. With a synthesizer, the possibilities really are infinite!

If you've got a microphone, you could try recording a snatch of your own voice (or some other sound) and transforming it in various ways—changing the frequency, adding effects, and so on. That's effectively what people do when they're sampling.

And for your next trick...

While you can certainly create some interesting sounds with Audacity, they have to be individually built around specific frequencies. There's no way to create a sound with a certain character and then transpose it up and down a scale, as you'd do with a normal musical instrument; in other words, you can't play tunes. So once you've mastered Audacity (or exhausted it, depending on your point of view), it's time to move on to a real synthesizer.

Screenshot of Modular Synthesizer, an analog synthesizer app from Pulse Code, Inc.

Photo: Modular Synthesizer is an iPhone app that replicates an analog, modular synthesizer on your smartphone—even down to the neat, old-fashioned "patch cords" (cables) that connect different modules together. Search on "synthesizer" in your favorite app store and you'll find all kinds of neat synthesizers you can play with, from simple on-screen keyboards right up to authentic gadgets like this one, which can export your tunes direct to sites like Soundcloud.

Assuming you haven't got access to an actual synth, nip along to your favorite app store and search for "synthesizer." On the iPhone/iTunes store, you'll find quite a few very realistic synth apps like Modular (from Pulse Code), KORG Gadget (from KORG themselves), and Peter Vogel CMI (a faithful, mini-reproduction of the classic Fairlight CMI synthesizer from the 1980s produced by its original inventor). Over in Android land, Common Analog Synthesizer (from oxxxide) is a great place to start; very similar to the basic subtractive synthesizer I outlined above, it has two oscillators (offering a choice of sine, square, pulse, and sawtooth wave), an ADSR filter, an ADSR amplifier, an LFO, and a few other bits and pieces. If you haven't got a smartphone or tablet, don't despair; there are also various PC synthesizer programs (such as the CM101 produced a few years ago by Muon Software and now superseded by various improved models).

Screenshot of Common Analog Synthesizer Android app by oxxxide.

Artwork: A screenshot of Common Analog Synthesizer by oxxxide. Although it has only a puny keyboard (which you can scroll up and down for higher and lower notes), it's a surprisingly powerful demonstration of basic subtractive synthesis and a good place to go next.

Who invented synthesizers?

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There's no substitute for hearing synthesizers—so here's a selection for your delight. These videos are mostly about historic synths from the 1970s and 1980s:


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Text copyright © Chris Woodford 2007, 2022. All rights reserved. Full copyright notice and terms of use.

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