Glenn Poorman, June 2011
Updated from an article originally written in June, 2008.

Contents

• Introduction
• Sound (simple version)
  • Pitch
  • Timbre
  • Loudness
• The Basic (Subtractive) Synthesizer
  • Oscillator (pitch)
  • Filter (timbre)
  • Amplifier (loudness)
• A Better (Subtractive) Synthesizer
  • More Oscillators
  • Noise Generator
  • Envelope Generator
    • Amplifier Envelope
    • Filter Envelope
  • Low Frequency Oscillator (LFO)
• More Bells and Whistles
  • Portamento (Glide)
  • Arpeggiator
  • Step Sequencer
  • Polyphony
  • Effects
• How Some Classic Units Worked
  • Moog Modular
  • MiniMoog
  • ARP 2600
  • Roland Juno-60
  • Roland GAIA SH-01
• Software
• Conclusion

Introduction

My interest in synthesizers goes back to the early 70s. As a very young music student, I was paired with a local high school student for lessons and I ended up studying with her for several years. Her musical tastes and knowledge of genres covered a lot of ground and she regularly opened my eyes to things well outside my narrow field of vision including the world of synthesizers. We would listen to the Beach Boys and talk about the use of the Theremin. We listened to Henry Mancini and talked about the synthesizers he used in the TV themes for "The Mystery Movie" and for "Cade's County". We talked about the work of Wendy Carlos and the instruments built by Bob Moog. We talked about the ARP units that fueled some of Pete Townsend's work as well as Edgar Winter's "Frankenstein".

In 1979, I managed to briefly put my hands on a real synthesizer while attending the Summer Arts Camp at Interlochen. The instrument was made by Univox. I was in the high school jazz ensemble that summer and our instructor brought the instrument along to loan to our piano player. For most of us this was a first so we were understandably anxious to give it a try. Then in 1984, I came into possession of the Roland Juno-60. By then I was recording my own music and the 121normal studio was in its second location. I had the Juno-60 for the better part of three years and used it in several of the recordings from that era.

In spite of all the time I put into the Juno-60, I still never really understood how it all worked. I just tweaked knobs and sliders until I got the sounds I liked. I was able to save the sounds in memory so I wouldn't have to repeat my hunt and peck process every time I fired it up. After a while, I simply became good at remembering what the various sliders did even if I didn't really know why they did it (turn that doohickey over there so the note makes that "dwap" sound).

After taking a brief hiatus in the late 80s, analog synthesizers made a huge comeback during the 90s. As we moved into the 21st century, computers took over and the newest synthesizers came in the form of software. While the heart of today's software synth works very much like its hardware ancestors, the almost unmeasurable amount of additional control makes that hunt and peck method of creating sounds that served me so well on the Juno-60 virtually impossible today. There are simply too many variables. For many hobbyists, this isn't necessarily a problem as both modern hardware and software synths come with enough presets to keep the average user busy for the life of the synth. If you want to go off and create your own sounds though, a basic understanding of sound synthesis has become an absolute must.

So what is a synthesizer? By its very definition, a synthesizer is something that produces by synthesis or by combining parts to form a whole. An electronic music synthesizer provides components to simulate the various aspects of sound and then those components are combined to produce what we finally hear.

There are several methods of synthesis used in both hardware and software units including subtractive synthesis, additive synthesis, frequency modulation synthesis (also called FM synthesis), wavetable synthesis, and sample based synthesis (just to name a few). Many of today's units, especially the software units, will combine several methods of synthesis allowing the user to choose the method they want to use. For our purposes, we'll focus on subtractive synthesis as this method was used by the original units of the 60s and tends to be the most popular (and easiest to understand).

Sound (simple version)

Of the many definitions of the word sound in the American Heritage Dictionary of the English Language, the first reads as follows:

vibrations transmitted through an elastic solid or a liquid or gas, with frequencies in the approximate range of 20 to 20,000 hertz, capable of being detected by human organs of hearing.

That's a fairly cold definition for something that can be so moving when it comes in the form of music. It's also a very human-centric definition as we know that other members of animal kingdom are capable of detecting sounds well outside the range of 20 to 20,000 hertz and that many instruments generate frequencies outside of that range as well. For our purposes though, the heart of that definition works.

In musical terms, a sound is essentially made up of three components.

• Pitch

  The pitch is the frequency of the sound or in musical terms, the note. It is determined by the number of times a sound wave repeats itself within one second of time. A single repetition of the sound wave is called a cycle and the number of cycles that occur in a second is called the frequency.
  

• Timbre

  The timbre of a sound is that quality that allows us to (for example) distinguish the sound of a piano from the sound of a clarinet or a human voice. Most sounds are actually made up of an array of pitches all at different frequencies. The base frequency is called the fundamental while the additional frequencies are called overtones or harmonics. The fundamental combined with the overtones makes up the harmonic series. The timbre of an acoustic instrument is going to be determined as much by the shape, size, and material of that instrument as it is by the origin of the tone itself. That is because those aspects of the instrument's design will naturally suppress or filter certain frequencies in the harmonic series giving that instrument its unique sound.
  

• Loudness

  Loudness or volume is exactly that. The volume of the sound. Every sound has some amount of volume both initially and over time. The sound also has a beginning and an end as well as an initial attack and decay.

The Basic (Subtractive) Synthesizer

In simplest terms, subtractive synthesis subtracts harmonic content from a sound by passing that sound through an audio filter. The basic subtractive synthesizer is generally broken up into three sections corresponding directly with the three basic components of sound. Those three sections are the oscillator (pitch), the filter (timbre), and the amplifier (loudness). On the original analog synthesizers, these components were all voltage controlled and were frequently referred to as the VCO (voltage controlled oscillator), VCF (voltage controlled filter), and VCA (voltage controlled amplifier). It's not uncommon to see the old acronyms still in use today even on units that are no longer voltage controlled.

Let's take a look at what would be the world's simplest and most basic subtractive synthesizer and then discuss the sections in greater detail.

• Oscillator (pitch)

  The oscillator section corresponds to pitch and is the heart of the synthesizer. This is where the waveform is generated. The frequency of the oscillator determines the pitch. There are a variety of ways that the frequency might be determined but the most common is through the press of a key on a piano-style keyboard. Even the simplest of synthesizers will offer their user a selection of waveforms to choose from. At a minimum, the selection will likely include a square wave, triangle wave, and sawtooth wave as well as a sine wave. These basic waveforms are shown in figure 2.
  
  
  
  Figure 2. Basic
  Wave Shapes
  
  These waveforms generate distinctly different tones as you can hear in the samples below. Each sample plays the identical arpeggio using different wave selections. The sine wave consists of only the fundamental and has a very mellow tone to it. The triangle contains the odd harmonics but there is a decrease in amplitude in the upper harmonics. The square wave contains all of the odd harmonics and has a sound that resembles a clarinet. The sawtooth contains all of the harmonics and sounds more brassy.
  
  Many units also provide a pulse wave (sometimes referred to as a rectangular wave) which is similar to the square wave except that the upper and lower parts of the wave are not symmetrical. The width of the upper part of the wave (referred to as pulse width) can be set by the user and is usually measured as a percentage of the entire cycle (where 50% is the equivalent of a square wave). These waves can resemble the sound of a saxophone or oboe depending on where the pulse width is set.
  
  Figure 3. Pulse Wave
  The sample below plays the same arpeggio again using a pulse wave with the pulse width set at around 20%.
  
  

• Filter (timbre)

  Once the sound is generated, the next stop is the filter. As we discussed in the section on sound, a sound generated by any source is going to be made up of an array of frequencies that make up the harmonic series. On acoustic instruments, filtering of those frequencies occurs naturally as a result of the characteristics of the instrument itself. On the synthesizer, the filtering is user controllable. A waveform generated by an oscillator will originate with the full spectrum of frequencies characteristic of that waveform. Using the filter, the sound can be modified by removing and/or enhancing frequencies in the harmonic series. The most common type of filter used in synthesizers is called a low pass filter. The low pass filter allows lower frequencies to pass through while removing higher frequencies that reside above a certain cutoff frequency. This is where the subtraction in subtractive synthesis occurs and this cutoff value is controlled by the user.
  
  The following sample plays a single tone using a sawtooth wave. The tone starts with all of the frequencies audible, slowly decreases the cutoff value, and then slow increases it again.
  
  Some synthesizers will also include a high pass filter which works just the opposite of the low pass filter. In other words, the high pass filter allows higher frequencies to pass while removing frequencies below the cutoff.
  
  The following sample plays the single sawtooth tone again with all frequencies audible. Then the cutoff value is slowly increased and then slowly decreased again.
  There are other types of filters you might see depending on the unit or software. The band pass filter allows frequencies within a certain range or band to pass through while rejecting frequencies outside of that range. The comb filter removes frequencies across the spectrum resulting in a frequency response consisting of a series of spikes (resembling a comb).
  
  In addition to removing frequencies, the filter also allows frequencies to be enhanced by feeding a portion of the signal at the cutoff frequency back through the filter again. This control is referred to as resonance. Adjusting the resonance can generate some interesting sounds and is responsible for some of the classic sounds that people consider to be the most "synthy."
  
  In the samples below, we play the single sawtooth tone again and play with both the cutoff frequency and the resonance demonstrating how the two interact with each other. In the first sample, we'll set the cutoff at a middle of the road location and vary the resonance. In the second sample, the resonance is turned up fairly high and the cutoff frequency is varied.

• Amplifier (loudness)

  The amplifier section of the synthesizer controls the volume of the sound. On an analog synthesizer, the oscillators never really stop oscillating. They are generating their waveform all of the time but that sound is patched into the amplifier where it is stopped with a zero volume (like a river running into a dam). The sound is then essentially cut loose via a key press and makes it to your ear at the volume set on the amplifier.
  
  The volume is a simple adjustment as it is on any piece of audio gear. When a sound is generated (not taking any additional components into account), it is immediately heard at the volume the amplifier is set at until such time that the sound is stopped and just as immediately goes quiet. This is the basic tone you can hear in the sample below.

A Better (Subtractive) Synthesizer

The basic synthesizer from the previous section, while a useful teaching tool, isn't much good for anything else. Only the most basic tones are possible and the character of those tones is fairly cold. There has never been a single commercially available synthesizer, however, that didn't come with some extra bells and whistles to color up the tone and make it a bit more interesting.

• More Oscillators

  To start with, even the most basic synthesizer comes with at least two oscillators allowing you to generate more than one waveform at a time. The additional waveforms are generated from the same key stroke as the primary waveform so they sound in unison. The shape of the waveform can be independently set on the additional oscillators. The frequency of the added oscillator can also be set. On some units, only the added oscillators have a frequency setting and that setting is relative to the frequency of the first oscillator. On other units (and in the figure below), all oscillators have a setting allowing the frequency to be set relative to the original key press.
  
  
  
  Figure 4. Basic synth with two oscillators
  
  The samples below illustrate the sound of two oscillators triggered by the same note with varied waveform and frequency settings. In the first sample, both oscillators play the same notes but each has a different waveform. This simply adds some body to the overall tone. In the second sample, both oscillators generate a sawtooth wave but the frequency of the second is set such that it sounds a full octave above the first. In the third sample, each oscillator generates a different waveform and the frequency of the second is set such that it sounds a perfect fifth above the first.

• Noise Generator

  In addition to the oscillators themselves, the oscillator section of any synthesizer will also include a noise generator. This does exactly what you would expect based on the name. That is, it generates noise (think of the sound of a television or radio that is not getting a signal). Noise is generally characterized as the presence of all possible frequencies at once. Some units will offer a selection between white noise (where the amplitude of the frequencies is even across the spectrum) or pink noise (where the amplitude falls off across the spectrum).
  
  
  
  Figure 5. Two oscillators and a noise generator
  
  The samples below illustrate both white noise and pink noise by themselves as well as the sound of noise generated along side a single sawtooth wave.
  
  Upon first listen it might sound as if the noise generator doesn't really bring much to the table. In the samples above, the use of the noise generator sounds like ... well ... noise. But in context, it can be very useful. The most common use is to create percussive sounds (like a snare drum). Noise is also used to provide some special effects sounds as well. One of the samples below illustrates a synth line where some percussive sounds created by the noise generator are mixed with some tones. The other sample uses the noise generator to create the sound of surf.

• Envelope Generator

  In addition to the three basic components of sound described way back in the section on sound (pitch, timbre, loudness), a sound is also shaped by an initial attack and subsequent decay in both volume and filtering of frequencies. This attack and decay shape is referred to as an envelope and the type of envelope used in sound synthesis is referred to as an ADSR envelope (where ADSR stands for Attack, Decay, Sustain, and Release).
  
  
  
  Figure 6. Typical ADSR envelope
  
  Your basic synthesizer will contain at least two envelope generators used to control the initial attack and decay of a sound's volume and also the initial attach and decay of the filter cutoff frequency. That means one will be added to the amplifier section of the synth while a second will be added to the filter section. These envelope generators along with the other components we've already discussed make for a much more realistic looking analog synthesizer as seen in figure 7.
  
  
  
  Figure 7. A more realistic synthesizer

  • Amplifier Envelope

    In the amplifier section, the envelope is used to control the attack and decay of the volume and the parameters can be described as follows:
    
    
    • Attack - how long it takes for the tone to go from zero volume to full amplifier volume once the key is pressed.
      
      
    • Decay - how long it takes, once the tone has reached full volume, to decay down to sustain level.
      
      
    • Sustain - the level the tone plays at after the decay time has passed. This cannot be higher than the amplifier volume so you could think of it as a percentage of the amplifier volume.
      
      
    • Release - how long it takes for the tone to go from sustain level down to zero once the key is released.
    
    In order to further describe how these settings relate to the final sound, let's look at some settings and listen to the effect. There are couple of important things to point out before we do so however.
    
    
    1. To understand how the ADSR settings apply to what you're hearing, it is important to know the duration of the notes. For each of the samples below, we use the identical phrase made up of four quarter notes with quarter rests in between.
       
       
    2. The values used for the ADSR settings will vary from manufacturer to manufacturer. For our purposes, let's assume that the value range for each parameter is 0 to 10.
    
    
    Start with the basic tone from the amplifier section. This is the tone that started and ended so abruptly. That tone is the result of setting A (attack) = 0, D (decay) = 0, S (sustain) = 10 and R (release) = 0. It's important to note here that since the S value is set to the maximum, the setting of the D value has no effect (since we have nowhere to decay to).
    
    The next sample plays the identical phrase but increases the attack to 8. This gives us a long fade in. Still using the maximum sustain value and no release value, the note fades in and then cuts off abruptly.
    
    In the next sample, the phrase is played again but here there is a low attack value, a medium decay value and then a low sustain value. The release value is still zero so the result is a note that swells to full volume quickly, then just as quickly decays to a lower volume, and then cuts off abruptly again.
    
    In the last sample we set the envelope just as we did for the basic tone (attack = 0, decay = 0, sustain=10) but we slightly increase the release value. The result is that the tones appear to sound longer because there is a decay after the note ends as opposed to an abrupt cutoff.
    
    

  • Filter Envelope

    The envelope in the filter section works exactly as it did for the amplifier section except that, in this case, it is the filter cutoff that varies instead of the volume. The envelope parameters are the same but their effect is a little different.
    
    

    NOTE: In the parameter descriptions below, I will refer to the minimum and maximum cuttoff frequency value. On the unit I used to generate the samples, the minimum value is determined by the cutoff frequency the filter is currently set to while the maximum value is whatever the maximum for that cutoff can be (likely 20,000hz). All filter envelopes essentially do the same thing but I've seen variances in how they relate back to the original cutoff frequency setting. In other words, you might have to experiment with your particular synth to get the same results.

    • Attack - how long it takes for the cutoff frequency to go from the minimum to the maximum value.
      
      
    • Decay - how long it takes, once the cutoff frequency has reached its maximum, to decay down to the sustain value.
      
      
    • Sustain - the cutoff frequency after the decay time has passsed.
      
      
    • Release - how long it takes for the cutoff frequency to go from sustain level down to the minimum once the key is released.
    
    The samples below use the identical phrase used in the amplifier envelope samples made up of four quarter notes with quarter rests in between. In all but the last sample, the settings for the amplifier envelope are A=0, D=0, S=10, R=0.
    
    In the first sample the initial cutoff frequency on the low pass filter is set to zero. We then put a low attack value on the envelope which will cause the cutoff to increase from it's attack value to the maximum fairly quickly. We follow that with a mid-range decay value and a zero sustain value. This means that shortly after sounding, the cutoff will decrease to zero. The release on both the amplifier and filter envelope means the notes cut off abruptly. Note how the use of the envelope on the filter gives the overall sound a low brass quality (like a trombone).
    
    To exaggerate the filter envelope, the next sample plays the identical phrase using the identical settings for both the filter and amplifier envelopes. The difference here is that we turn up the resonance on the filter to really bring out the effect.
    
    The last sample is a little tricky to understand. In this sample, instead of using a decay value to get that wah effect, we set the envelope such that once the attack is finished, the note stays at the full spectrum. We then add a slight release value so that the cutoff will decrease after the note ends.
    
    The tricky part here is that since the release on the filter only kicks in after the note ends, you'll never hear the effect unless you also increase the release value on the amplifier envelope. So for this sample, we set the release on both the filter and amplifier envelopes to be the same.
    
    

• Low Frequency Oscillator (LFO)

  Another common addition seen on most synthesizers is the low frequency oscillator (or LFO). The LFO is used for modulation effects and unlike the oscillator used to generate a tone, the LFO generates a signal at a frequency that is below 20Hz creating a pulsating rhythm rather than an audible tone. On some units, the LFO might be its own specialized oscillator. On other units, one oscillator might be designated to serve either purpose (tone generation or LFO but never both at the same time). In either case, the LFO can be used to modulate pitch and/or filter cutoff.
  
  As with any oscillator, the waveform for an LFO can be set by the user and just like with a tone, the different waveforms product different results. The samples above both used a nice smooth sine wave. Note the difference in the next sample that uses a sawtooth wave to modulate the pitch.
  Another common use of the LFO is to modulate the pulse width. If you recall from the initial discussion of oscillators, a pulse wave (or rectangular wave) is similar to a square wave except that the upper and lower parts of the wave are not symmetrical and this pulse width can be set by the user. On most synthesizers, if your tone generating oscillator is set to generate a pulse wave, your LFO can be used to modulate the pulse width. This will be commonly referred to as pulse width modulation or PWM. The sample below illustrates a single oscillator generating a pulse wave and an LFO being used to modulate the pulse width.

More Bells and Whistles

What we've looked at so far could be considered the bare essentials. These are the components that a synthesizer would be useless without. Most (if not all) units will provide some other bells and whistles though to make the unit more interesting and more musical. The added components vary and there's no way to cover all of them but we can touch on some of the more common additions.

• Portamento (Glide)

  The dictionary defines portamento as a continuous gliding movement from one tone to another. This setting is often referred to as glide depending on the manufacturer. Using portamento, you can play an interval and hear a noticeable glide from one tone to the next. Synths with portamento will provide a speed setting so that you can adjust the speed of the glide.
  
  The samples below demonstrate portamento of various speeds. The first two samples use the same phrase at the same tempo. The third sample slows the phrase down a bit so you can hear the glide.

• Arpeggiator

  An arpeggiator function will repeat notes that you hold down on the keyboard in sequence. For example, if you hold down a simple C major triad (C-E-G) with the arpeggiator function turned on, you will hear the notes repeat sequentially (like an arpeggio) as long as you hold the keys down. The speed and manner in which the notes repeat are generally user settings. Those settings will include speed, number of octaves and the pattern (up, down, random, etc).
  
  The samples below demonstrate the arpeggiator function on a simple C major chord (C-E-G-C) varying the arpeggiator settings. The last sample adds a little portamento for some extra flair.

• Step Sequencer

  The step sequencer is similar to the arpeggiator but it can do much more. In simplest terms, the step sequencer allows the user to alter synth parameters over a series of steps at a given rate. The basic settings on the step sequencer are the number of steps and the speed. The steps are broken up evenly and repeat at the given speed. The most obvious use of the step sequencer is to set it up to sequence pitch. Given a note (determined by pressing a key), you can setup the sequencer at each step to vary the pitch relative to the original note thus automatically playing a phrase. You could think of it like an arpeggiator except that, instead of using multiple keys to determine the notes, the notes are defined ahead of time relative to just a single key.
  
  That's just the beginning though. With a step sequencer, you're not confined to only varying pitch. You can patch the sequencer into many of the synth's parameters and even patch it into more than one parameter at a time. For example, you could just patch the sequencer into the filter cutoff. So now when you press a key, the note simply repeats but with each repetition comes a change in the filter cutoff which you can program at each step. Or you could patch the sequencer into both the pitch and the the filter cutoff varying both.
  
  The samples below demonstrate some step sequencer uses.
  
  If you want a good example of that sequenced filter usage, the next time you have on a classic rock station and they play Emerson, Lake and Palmer's "Karn Evil 9: 1st Impression - Part 2", listen for that filter sequenced beginning just before Greg Lake starts in with "Welcome back my friends to the show that never ends ..."
  

• Polyphony

  One limiting aspect of the early synthesizers was their lack of polyphony or the ability to play more than one note at the same time. This was largely a matter of cost as polyphony required additional oscillators and a host of added circuitry to make it work. Some early attempts at polyphony involved a marriage of synthesizer circuitry and electric organ circuitry. The most notable of these attempts were the ARP Omni and the PolyMoog. Yamaha was one of the first companies to offer real polyphonic synthesizers such as the CS-80 but these units were heavy and costly. The first polyphonic unit to get wide usage was the Prophet 5 made by Sequential Circuits. By the early 80s, polyphonic units became the norm. Later as more units started going digital, voice limitations became virtually non-existent.
  
  Listen to some polyphony samples below.
  
  Note about that last sample: In the overlapping notes sample, we set the release value on the amp envelope somewhat high and play a single note passage. You might be thinking that you could do this with a monophonic synth and you would be correct. The difference, however, is that that once you played the next note on a monophonic synth, the release on the previous note would be immediately interrupted. In the sample above, the release continues to ring while the next note sounds because the unit is polyphonic.
  

• Effects

  As the circuitry inside of the various synth modules began to go digital, manufacturers starting introducing effects into their units. The extent of the effects generally depends on the unit but at a minimum, today's synth units (either hardware or software) will provide the time based effects such as chorus, delay, flanger and reverb.
  
  The samples below show how effects can be used to spruce up some simple synth patches.
  
  In this last sample, we'll use a patch from the Arturia Moog Modular simulation to combine a couple of features and have some fun. This is a step sequencer patch varying both the pitch and the filter with a long digital delay applied for a really cool sequence. The sample is the result of simply holding down middle C for a couple of measures.
  

How Some Classic Units Worked

Synthesizers have been commercially available since the 60s. Ever since the very first units hit the scene, the trick as a manufacturer has always been to provide the customer with all of the control that makes these units so powerful but present that control in such a way that can be easily learned and understood. For the most part I believe they succeeded. But to really get the most out of any synth unit (either then or now) you still need to know the basics. Let's take a quick overview at some of the classic synths that have existed over the years and how they map back to the components discussed here.

• Moog Modular

  The Moog Modular system was the first from pioneer Bob Moog. These systems hit the market in the early to mid 60s, were made to order, and were very expensive. At first glance, most people thought these units were a bit insane and wondered how anyone could possibly figure out how to use them. Some of the larger systems filled entire walls with patch cords hanging in every direction. Once you got beyond the initial visual though, the Moog Modular systems were actually brilliant in their simplicity.
  
  
  
  Figure 8. Moog Modular System
  
  These systems used the components we already discussed and really nothing more. How many of these components came in your system was up to you as a customer and how much you were willing to spend. The voltage controlled oscillators, the filters, the amplifiers, the envelope generators and everything else were all built as separates. When you decided how many of each you wanted, Moog built your system into some nice cabinetry and your custom synth was born. By itself, the system was nothing more than a bunch of discrete components in a larger box and made no sounds. To create your sounds, you had to decide what components to use in what order and then create your path using a series of patch cords.
  
  So for example, say you wanted the basic sawtooth wave with no envelope or no filtering applied. You could set the waveform selection on one of your oscillator components to sawtooth and then run a patch cord from the output of that oscillator to the input of one of your amplifiers. Turn the volume up on that amplifier and you're done.
  
  Now if you want to add some filtering and an envelope on the amp, run a patch cord instead from the oscillator to a filter, another cord from that filter into an envelope generator, and then another cord from that envelope generator into an amplifier. Set your cutoff and resonance on the filter, your ADSR settings on the envelope generator, the volume on the amp and you are done once again. After that you can patch an LFO into the oscillator or filter if you want.
  
  Of course these are just a couple of very simple examples. You can have any number of oscillators, filters, amps, etc with patch cords running in every direction. On top of all that, Moog also made an amazing step sequencer for the Modular system.
  
  While the system came into existence in the early to mid 60s, the Moog Synthesizer was put on the map when Wendy Carlos recorded Switched on Bach, a brilliant example of what these systems could do and a recording that still holds up today.
  
  

• MiniMoog

  In 1970, Moog introduced the MiniMoog. The MiniMoog was a small unit designed to be more affordable and approachable by the average musician. With this unit, Moog made some decisions to what most players would want or need in a compact unit wiring just a handful of components all together into a single package.
  
  
  
  Figure 9. The MiniMoog
  
  The MiniMoog had three voltage controlled oscillators and one noise generator. The third oscillator could be used to generate a tone or as a low frequency oscillator. The noise generator created a mix of white and pink noise. The unit contained one filter and one amplifier each with its own ADSR envelope generator. All in all a very similar unit to what was diagrammed here back in the section on envelope generators.
  
  

• ARP 2600

  The ARP 2600 was introduced in 1971 by ARP Instruments Inc. This was the first unit designed to be a hybrid of a wired and modular system. Out of the box, the unit generated sound and there was a fair amount you could do just using the knobs and sliders. Similar to the Moog Modular system though, a series of patch cords could be used to really open the unit up.
  
  
  
  Figure 10. The ARP 2600
  
  The most notable parts of this system were the overall wonderful sound of the ARP oscillators and also the step sequencer. The unit packed much of the power of a larger modular system but was considerably more compact. During the 70s the ARP 2600 proved to be one of the more popular synthesizer units being used by the likes of Pete Townsend, Brian Eno, David Bowie and Herbie Hancock. Perhaps the most notable use of this unit was by Edgar Winter who absolutely ripped lead lines, accompaniments and sequences in the song Frankenstein.
  
  

• Roland Juno-60

  In 1982 Roland introduced the Juno-60 which is probably still their most popular synthesizer to this day. This era was really the dawning of the age of polyphony. Sequential Circuits had already released the Prophet 5 which was really the first unit that put polyphony into a package that was reasonable to manage and was also one of the first units to introduce patches. The Juno-60 followed up with similar functionality and a lower price tag.
  
  
  
  Figure 11. The Roland Juno-60
  
  The Juno-60 swapped out the familiar voltage controlled oscillator (VCO) for a digitally controlled oscillator (DCO). These oscillators overcame tuning issues that could occur with the earlier VCO components by controlling the frequency with a microprocessor. The oscillator itself was still fully analog. The unit was 6-voice polyphonic with one DCO per voice which also contained a sub-oscillator capable of generating a tone one octave below the fundamental.
  
  The overall sound of the Juno-60 was superb. During the 80s, the Juno-60 was one of the mainstays of pop music and was used by numerous popular artists. Personally I had an almost obscene amount of fun with the Juno-60 and still regret letting it go.
  
  

• Roland GAIA SH-01

  Introduced in 2010, the Roland GAIA SH-01 is hardly a classic. It is a small inexpensive unit that has barely been on the market for a year. It warrants a little discussion for a couple of reasons though.
  
  
  
  Figure 12. The Roland GAIA SH-01
  
  First, the SH-01 is one in a line of many of today's fake analog synthesizers. These low priced units look and are controlled like a real analog synth in every way but they are digital units modelling the analog world. This is ok really. Many of them sound really good and the price is right.
  
  The other thing I particularly like about the SH-01 is that it is possibly the best unit today to use as a synth teaching tool. If you read an article such as this one and then study the control panel on the SH-01, you will recognize just about everything you see immediately. The sections are logically laid out and extremely easy to tweak. For the money, I don't believe you'll find a unit that is more fun to play with.

Software

Today, software synthesizers are everywhere. These are synthesizers that come in the form of software for your computer. These programs can be used as stand alone synthesizers allowing you to generate the tones via a MIDI keyboard controller (or any other kind of MIDI controller). The same programs can also be used as plug-ins for your favorite DAW software allowing MIDI tracks to be recorded and then assigned to the synthesizer plug-in for playback. They are a revolution and keeping track of them all is virtually impossible. Many of these synths are, at their heart, subtractive synthesizers simulated via software. Many are a combination of different kinds of synthesizers including but not limitied to subtractive synths.

• Classic Emulations

  Classic emulations are very much in style right now. That is, software synthesizers that emulate vintage units. In most (if not all) cases of classic synth emulation, firing up the software brings up a display that looks just like the original hardware unit. One example of this is the MiniMoog emulation by Arturia shown below.
  
  
  
  Figure 13. Arturia Minimoog Display
  
  Using a program such as Arturia's Minimoog, you control your synth and setup your sounds by using the knobs and switches exactly as you would on the original unit. Arturia even makes a Moog Modular and ARP 2600 emulation (shown below) that requires the use of virtual patch chords to edit sounds. These virtual patch chords behave just like the real patch chords from the original hardware units. If you're looking to learn something about how these vintage units worked, you really can do so by studying the Arturia emulations. There are very well done.
  
  
  
  Figure 14. Arturia ARP 2600 Display
  
  Unlike the original units though, the niceties afforded via software are generally added into these packages such as polyphony and a host of digital effects. Using the Minimoog as an example yet again, the software wakes up as a monophonic unit so as to emulate the original exactly. Polyphony is easily turned on though and the number of voices is a configurable parameter. You can also add digital chorus and delay to the tone which was never available on a real MiniMoog unit.
  
  

• Beyond the Classics

  The real fun comes when you break out of the past and embrace the future. Software provides the ability to do things never done on the old hardware units and many manufacturers have embraced this and provided packages capable of generating sounds never heard before. Just about every DAW package comes with a host of stock synthesizer plug-ins. Third party manufacturers have poured serious development time into creating programs that could very well become legendary like some of the hardware units of the 60s, 70s and 80s.
  
  
  
  Figure 15. NI Absynth 4 Display
  
  My personal favorite software synthesizer is Absynth made by Native Instruments. Absynth comes pre-stocked with hundreds of sounds but, of course, allows the user to modify any sound or create new sounds from scratch. Combining many different kinds of synthesis, digging into the inner workings of Absynth can appear daunting. But if you start with a brand new sound and activate the patch window, you'll see some things you should recognize by now. Namely, an oscillator patched into a filter patched into an amplifier and an envelope generator.
  
  Of course, from there you can go wild adding oscillators, creating custom waveforms, generating an infinite number of envelopes controlling any of the hundreds of parameters. But if you break it all down, the basic premise is still very much like everything we've discussed here. Of course, the end results can be wild as demonstrated in the following sample generated from a factory Absynth patch and a single middle C on my USB keyboard.
  
  What kind of waveforms, filtering, and envelopes do you suppose it took to make that sound?

Conclusion

I loved synths when I first learned of them and have really never stopped. They allow you to continuously go beyond traditional sounds in music and create new ones. With the proliferation of software synths, more people than ever have access. For the most part, you can have a lot of fun picking apart the presets and experimenting in the dark. A good grasp of how synths work, however, will go a long way toward making your musical visions become reality. Armed with a little knowledge, you can not only create the sounds you want to create but you can also look at how some of those presets were created and say "aha ... THAT's how they did that". As with most things in life, a little knowledge can go a long way.

Most of all though ... it's fun! Lots and lots of fun!