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Synthesizer Fundamentals
Glenn Poorman, May 2008
With input, editing and hand holding from Sean Stirling.
Additional input from Mark Smart.
My interest in synthesizers goes back to the early 70s when I was a young saxophone student. In late grade school, I was hooked up for private lessons with a student from the local high school 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. Her father considered himself somewhat of an amateur inventor and had a great love for "toys" and so, between them, synthesizers were a frequent topic and he had a lot of recordings that featured the fledgling technology. We listened to the Beach Boys and talked 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 Pete Townsend's work on "Who's Next" as well as Edgar Winter's "Frankenstein" (the synth heavy favorite of every junior high kid in my home town). Over the course of the 70s, the use of synthesizers steadily grew in rock and contemporary jazz. The 80s then brought an absolute explosion as the New Wave sound became all about synthesizers and these instruments threatened to replace the guitar as the number one instrument in popular music.
It was 1984 when I came into possession of the Roland Juno-60. It was the first synth I managed to lay my hands on for more than five minutes. The unit actually belonged to a friend. He had stopped playing and left it with me for the better part of three years before finally re-claiming it and putting it up for sale. By then, I had already started recording my own music and the 121normal studio was in its second location. I put a lot of miles on that unit and the sounds of the Juno-60 permeated most of my recordings that came out of that time period. The funny thing is, I never really understood how the synthesizer worked or what the jargon on the controls meant. I just tweaked knobs and sliders until I got the sounds I liked. The Juno-60 allowed me 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).
Eventually analog units gave way to digital units and all the jargon was replaced with a simple selection of patches that allowed only a moderate amount of tweaking over digital samples. After a while though, people began to find the sound of the digital units to be a bit too sterile and started to pine for the fat warm sound of the old analog units. The 90s saw an influx of analog synths hitting the market and many acts, including the big names, were moving back to vintage synths. As we moved into the 21st century, computer technology took over and many synths came in the form of software that could operate as standalone computer programs or as plug-ins for your favorite DAW software. Some of these programs were specifically designed to emulate early analog units in every way. Others really took the whole idea of music synthesis to brand new heights allowing the creation of sounds never heard before. Regardless of which category these software synths fell into, at their heart they were driven by the same basic components that drove the early analog units and contained much of the same terminology. With the almost unmeasurable amount of additional control provided in today's units though, that hunt and peck method of creating sounds that served me so well on the Juno-60 is just about impossible today. 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 do want to go off and create your own sounds, a basic understanding of sound synthesis has become an absolute must.
If you're an old hand at synthesizers and are already intimately familiar with all of their components and how they work, then there's really no point in reading any further (unless you want to add yourself to the list of proof readers and editors). If you're like I was though and your eyes just sort of glaze over at the site of all those knobs and selections, this might make the perfect primer for you. In the sections that follow, I will describe the basic components that make up the simplest music synthesizer. While some of the terminology and functionality vary from unit to unit, I will attempt to keep the discussion as general as possible without discussing any specific vendors. Later, I'll touch on some added bells and whistles that many units added on and then get into some of the options software brings to the table.
Of the many definitions of the word sound in the American Heritage Dictionary of the English Language, the first reads as follows:
A sound is essentially made up of three components. Those components are pitch, volume, and time. The pitch is the frequency of the sound or in musical terms, the note. A sound also has some amount volume both initially and over time. The sound also has a beginning and an end as well as an initial attack and decay.
The timbre of a sound is the combination of those three building blocks and is the quality that distinguishes that sound from others. In musical terms again, the timbre is the quality that allows us to distinguish the sound of a piano from the sound of a clarinet or a human voice. A musical sound generated by any source is going to be made up of an array of pitches or frequencies. The base frequency is called the fundamental while the additional frequencies are called overtones. 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.
In addition to the filtering of frequencies, the timbre of a sound is also shaped by the sounds initial attack and subsequent decay in both volume and filtering. This attack and decay shape is referred to as the envelope.
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 actually several synthesis methods used in both hardware and software units today. The method used by the earliest units and the method we will focus on here is called subtractive synthesis. In simplest terms, this method of synthesis subtracts harmonic content from a sound by passing that sound through an audio filter.
Another method of synthesis is called additive synthesis. Using this method, the multiple harmonics that make up the timbre of an instrument are simulated by combining several waveforms. Each waveform has it's own volume and envelope and is pitched to one of the harmonics of the original note.
Other types of synthesis found in today's units also include Frequency Modulation Synthesis (also called FM Synthesis), Wavetable Synthesis, and Sample Based Synthesis (just to name a few). Many of today's units will actually combine several methods of synthesis into one unit.
For our purposes, we are going to focus on the early synthesizer models that used subtractive synthesis.
The main sections of a synthesizer are the oscillator (provides the initial sound with all its harmonic frequencies), the filter (allowing certain frequencies to be removed/enhanced providing more character to the sound), and the amplifier (providing volume). These three sections make up the basic components of the synthesizer. On the original analog synths, these parts were all voltage controlled and frequently referred to as the VCO (voltage controlled oscillator), VCF (voltage controlled filter), and VCA (voltage controlled amplifier). Among the original synthesizers and even among today's emulations, the terminology used will vary from product to product with some vendors using the english terms such as oscillator and others using the shortened acronyms like VCO.
We've covered the basics of the subtractive synthesizer. Most (if not all) units provide several other bells and whistles though to make the unit more interesting and 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.
Today, software synths are everywhere. 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 or a combination of a few different kinds of synthesizers including but not limited to subtractive synths. Going into detail on any of these synths is well beyond the scope of this writing. We can, at least, look at some of the synths I have on my own system and give a brief overview of them.
Synths are a blast no matter how you look at it. 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 now 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 take you a long way.
Most of all ... it's ridiculously fun!
With input, editing and hand holding from Sean Stirling.
Additional input from Mark Smart.
Contents
- Introduction
- Sound (simple version)
- Synthesis
- The Basic (Subtractive) Synthesizer
- Additional Components
- Software
- Conclusion
Introduction
My interest in synthesizers goes back to the early 70s when I was a young saxophone student. In late grade school, I was hooked up for private lessons with a student from the local high school 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. Her father considered himself somewhat of an amateur inventor and had a great love for "toys" and so, between them, synthesizers were a frequent topic and he had a lot of recordings that featured the fledgling technology. We listened to the Beach Boys and talked 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 Pete Townsend's work on "Who's Next" as well as Edgar Winter's "Frankenstein" (the synth heavy favorite of every junior high kid in my home town). Over the course of the 70s, the use of synthesizers steadily grew in rock and contemporary jazz. The 80s then brought an absolute explosion as the New Wave sound became all about synthesizers and these instruments threatened to replace the guitar as the number one instrument in popular music.
It was 1984 when I came into possession of the Roland Juno-60. It was the first synth I managed to lay my hands on for more than five minutes. The unit actually belonged to a friend. He had stopped playing and left it with me for the better part of three years before finally re-claiming it and putting it up for sale. By then, I had already started recording my own music and the 121normal studio was in its second location. I put a lot of miles on that unit and the sounds of the Juno-60 permeated most of my recordings that came out of that time period. The funny thing is, I never really understood how the synthesizer worked or what the jargon on the controls meant. I just tweaked knobs and sliders until I got the sounds I liked. The Juno-60 allowed me 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).
Eventually analog units gave way to digital units and all the jargon was replaced with a simple selection of patches that allowed only a moderate amount of tweaking over digital samples. After a while though, people began to find the sound of the digital units to be a bit too sterile and started to pine for the fat warm sound of the old analog units. The 90s saw an influx of analog synths hitting the market and many acts, including the big names, were moving back to vintage synths. As we moved into the 21st century, computer technology took over and many synths came in the form of software that could operate as standalone computer programs or as plug-ins for your favorite DAW software. Some of these programs were specifically designed to emulate early analog units in every way. Others really took the whole idea of music synthesis to brand new heights allowing the creation of sounds never heard before. Regardless of which category these software synths fell into, at their heart they were driven by the same basic components that drove the early analog units and contained much of the same terminology. With the almost unmeasurable amount of additional control provided in today's units though, that hunt and peck method of creating sounds that served me so well on the Juno-60 is just about impossible today. 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 do want to go off and create your own sounds, a basic understanding of sound synthesis has become an absolute must.
If you're an old hand at synthesizers and are already intimately familiar with all of their components and how they work, then there's really no point in reading any further (unless you want to add yourself to the list of proof readers and editors). If you're like I was though and your eyes just sort of glaze over at the site of all those knobs and selections, this might make the perfect primer for you. In the sections that follow, I will describe the basic components that make up the simplest music synthesizer. While some of the terminology and functionality vary from unit to unit, I will attempt to keep the discussion as general as possible without discussing any specific vendors. Later, I'll touch on some added bells and whistles that many units added on and then get into some of the options software brings to the table.
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. For our purposes though, the heart of that definition still works.
A sound is essentially made up of three components. Those components are pitch, volume, and time. The pitch is the frequency of the sound or in musical terms, the note. A sound also has some amount volume both initially and over time. The sound also has a beginning and an end as well as an initial attack and decay.
The timbre of a sound is the combination of those three building blocks and is the quality that distinguishes that sound from others. In musical terms again, the timbre is the quality that allows us to distinguish the sound of a piano from the sound of a clarinet or a human voice. A musical sound generated by any source is going to be made up of an array of pitches or frequencies. The base frequency is called the fundamental while the additional frequencies are called overtones. 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.
In addition to the filtering of frequencies, the timbre of a sound is also shaped by the sounds initial attack and subsequent decay in both volume and filtering. This attack and decay shape is referred to as the envelope.
Synthesis
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 actually several synthesis methods used in both hardware and software units today. The method used by the earliest units and the method we will focus on here is called subtractive synthesis. In simplest terms, this method of synthesis subtracts harmonic content from a sound by passing that sound through an audio filter.
Another method of synthesis is called additive synthesis. Using this method, the multiple harmonics that make up the timbre of an instrument are simulated by combining several waveforms. Each waveform has it's own volume and envelope and is pitched to one of the harmonics of the original note.
Other types of synthesis found in today's units also include Frequency Modulation Synthesis (also called FM Synthesis), Wavetable Synthesis, and Sample Based Synthesis (just to name a few). Many of today's units will actually combine several methods of synthesis into one unit.
For our purposes, we are going to focus on the early synthesizer models that used subtractive synthesis.
The Basic (Subtractive) Synthesizer
The main sections of a synthesizer are the oscillator (provides the initial sound with all its harmonic frequencies), the filter (allowing certain frequencies to be removed/enhanced providing more character to the sound), and the amplifier (providing volume). These three sections make up the basic components of the synthesizer. On the original analog synths, these parts were all voltage controlled and frequently referred to as the VCO (voltage controlled oscillator), VCF (voltage controlled filter), and VCA (voltage controlled amplifier). Among the original synthesizers and even among today's emulations, the terminology used will vary from product to product with some vendors using the english terms such as oscillator and others using the shortened acronyms like VCO.
Oscillator
The heart of the synthesizer is the oscillator. The oscillator generates the waveform. The frequency of the oscillator determines the pitch and that frequency is determined by the key that was pressed on the keyboard (or in a modern digital system, the MIDI note-on that was received). Most synthesizers will offer their user a selection of waveforms to choose from. At a minimum, the selection will likely include a square wave and sawtooth wave and might also include other shapes such as a triangle and sine wave. Some basic wave types are shown in figure 1.
Figure 1. Basic
Wave Shapes
These wave types generate distinctly different tones as you can hear in the samples below.
As you can hear from the samples, the square wave resembles the sound of a clarinet while the sawtooth wave sounds more brassy. Many units also provide a pulse wave which is similar to a square wave except that the upper and lower parts of the wave are not symmetrical. These waves can resemble the sound of a saxophone or oboe depending on where the pulse width is set.
Most synthesizers will also provide additional oscillators allowing you to generate more than one waveform at a time. These 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 additional oscillator can also be set allowing the added pitch to sound at an interval relative to the primary pitch.
Figure 2. Pulse Wave
The samples below illustrate the sound of two oscillators triggered by the same note with varied waveform and frequency settings.
Noise Generator
In addition to the oscillators themselves, the oscillator section of most synthesizers 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 that is not getting a signal). Just about all synth models provide the ability to generate pink noise and many models also provide an option to generate white noise.
In the samples below, we generate a tone that is pure white noise followed by a tone that mixes the noise generator with an oscillator generating a sawtooth wave.
Filter
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 its full spectrum of frequencies intact. 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 demonstrates a sawtooth wave that starts off open and slowly has the cutoff value decreased and then increased.
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 demonstrates the same sawtooth with a high pass filter applied and its value slowly increased and then decreased.
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 pretty wild sounds and is generally responsible for the sounds that people consider to be the most "synthy."
In the samples below, we 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, we vary both the resonance and the cutoff frequency.
Amplifier
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 that you finally hear is controlled by the two common parts of the amplifier section. Those parts are the volume and the envelope generator.
The volume is a simple volume adjustment as it is on any piece of audio gear. When a sound is generated (not taking the envelope into account which we'll discuss in the next section), it is immediately heard at the volume the amplifier is set at until such time that the sound is stopped and immediately goes quiet. That is the basic tone as you can hear in the sample below.
That is a somewhat harsh sound though. We can get more expressive by manipulating the attack and decay of the volume using the amp section's envelope generator.
Envelope Generator
In addition to the very basic components we've just described, the synthesizer will also contain at least two envelope generators. You will find one in the amplifier section and one in the filter section. These envelopes are used to vary parameters over time and are generally ADSR envelopes (where ADSR stands for Attack, Decay, Sustain, and Release).
In the amplifier section, the envelope is used to control the attack and decay of the tone 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.
- Release - how long it takes for the tone to go from sustain level down to zero once the key is released.
Figure 3 shows a typical ADSR envelope diagram.
Figure 3. ADSR Envelope
In order to further describe how these settings relate to the final sound, let's look at some settings and listen to the effect. The values used for the sliders or knobs that adjust the ADSR envelope will vary from manufacturer to manufacturer so, for our purposes, let's assume that the value for each of the parameters can be set to a value between 0 and 10.
Start with the basic tone again. The basic tone, as demonstrated above, 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).
In the next sample, we'll increase 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, we'll put a medium attack on the note followed by a medium decay down to a low sustain value. Still using a release of zero, the note cuts off abruptly again.
In the last sample, we'll cut the attack and decay back to zero, put the sustain back at full, and put a short release on the end.
As we mentioned at the start of this section, you will also find an envelope generator in the filter section of a synthesizer. The envelope works exactly as it did for the amplifier 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
passed.
- Release - how long it takes for the cutoff frequency to go from sustain level down to the minimum once the key is released.
In this sample, we use the basic tone (amp envelope is A=0, D=0, S=10, R=0). The cutoff frequency is set to zero as is the sustain frequency. We then put on a medium attack and a slightly longer decay .
So that sample started at the minimum (20hz), opened and then closed. Listen to the same sample again only this time, we'll turn up the resonance on the filter to bring out the effect.
In this last sample, we'll put a medium attack on the filter, set the decay to zero, the sustain to the maximum, and put a slight release on the filter.
NOTE: The release value only kicks in after the key has been released so if you have the release on your amp envelope set to zero, you'll never hear the effect of a non-zero release on the filter envelope. So for this sample, we set the release value on both the amp and filter envelopes to around three.
Note how the use of the filter envelope gives the overall sound a brass instrument quality (like a trombone).
Envelopes are a lot of fun to play with and when you move beyond the very basic hardware synths or into software synths, you'll find multiple envelope generators that can be assigned to any parameter on your synth.
- Attack - how long it takes for the tone to go from zero
volume to full amplifier volume once the key is pressed.
Low Frequency Oscillator
A low frequency oscillator (or LFO) is used for modulation effects. Unlike the oscillator used to generate tones, the LFO generates a signal that is generally below 20Hz creating a pulsating rhythm rather than an audible tone. The frequency and waveform of the LFO is usually adjustable and generally the user will have the option of using the LFO to modulate pitch and/or filter cutoff as in the samples below.
Like envelopes, LFOs on the newer units or software synths can be used to modulate just about any parameter or any function in your synth. Multipe LFOs setup to modulate multiple parameters at varying frequencies and depths can be used to create some very interesting sounds.
Additional Components
We've covered the basics of the subtractive synthesizer. Most (if not all) units provide several other bells and whistles though to make the unit more interesting and 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
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. The last sample is a very stripped down version of the phrase.
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.
- One octave ascending
- Two octaves descending
- Three octaves in a random pattern
- Same random pattern with portamento
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 filter cutoff varying both.
The samples below demonstrate some step sequencer uses.
- 8 step sequencer varying pitch
- 8 step sequencer varying filter cutoff
- 8 step sequencer varying pitch and cutoff
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 and complications required 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. Their success gave way to the popular polyphonic units used in the 80s like the Roland Juno-60 and the Korg DX-7. As more units went digital or digitally controlled, the voice limitation became virtually non-existent (120 voice polyphony).
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.
Software
Today, software synths are everywhere. 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 or a combination of a few different kinds of synthesizers including but not limited to subtractive synths. Going into detail on any of these synths is well beyond the scope of this writing. We can, at least, look at some of the synths I have on my own system and give a brief overview of them.
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 4. Arturia Minimoog Display
Many of these programs can be used as standalone synths or as plug-ins in your favorite DAW packages. As a standalone, sounds can be generated by hitting the keys on the display using your mouse or by playing a MIDI keyboard hooked up to your computer. As a plug-in, a software synth can be fully integrated into your recording studio.
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.
Figure 5. 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.
Beyond the Classics (Absynth 4)
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. One of my favorites is Absynth 4 made by Native Instruments. Absynth comes pre-stocked with hundreds of sounds and dissecting any of them can be a little overwhelming. But if you activate the patch window, then go to the "File" menu and select "New Sound" you'll see the simplest possible patch you can have in Absynth and you'll see some things you should recognize by now. Namely, a single oscillator generating a single sine wave.
Figure 6. Basic Absynth Oscillator
You can click on the word "Sine" and change the wave shape. This selection brings up a huge selection of different wave forms from the very basic to some very complex forms. Absynth even allows you to create your own custom wave forms.
Just under the oscillator in Absynth's patch window is a filter block which defaults to being disabled. A single click wakes the filter up providing selections of several different kinds of filters as well as the parameters that control them. The default filter type is the low pass filter and the available controls are the cutoff frequency and the resonance, two parameters that should be very familiar to you by now.
Figure 7. Absynth Oscillator and Filter
Absynth allows three chains of oscillator and modifiers. Each chain has two possible modifiers and these can both be filters as well as other modifiers such as ring modulators or frequency shifters. In another window, the "envelope" window, you can control both the master envelope for the whole patch as well as envelopes for individual parameters. In the figure below, you can see the envelope for the first oscillator's volume. Since we're in software though, you can look at it as an envelope diagram and edit that envelope graphically.
Figure 8. Absynth Envelopes
In Absynth, you can create any number of envelopes and assign them to any parameter. These envelopes can be as complex as you care to make them. They default to your standard ADSR envelopes but then allow the addition of breakpoints allowing the envelope to become much more complex. In the following diagram and sound sample, we apply an envelope to the pitch of the first oscillator changing the pitch over time to approximate an old step sequencer. In addition we also apply an envelope to the filter cutoff so that the cutoff varies over the same amount of time as the pitch. In both cases, we use another Absynth feature and that is to set both envelopes to "Retrigger" every 4 beats which will make the envelope shape repeat.
Figure 9. Envelopes applied to pitch and filter
With the those two envelopes applied, we can hold down a middle C for four measures and get the following sound:
Another cool Absynth feature is the ability to morph from one wave into another. With a single oscillator, you can load up two wave forms. The morphing from one wave into another can be done a variety of ways. You can manually drag the control to perform the morph. You can also assign either an LFO or an envelope to the morphing parameter. In the following sample, we load a Sine wave and a wave that sounds like an organ. We then assigned an envelope to the morphing parameter. The envelope is a simple ADSR setup to retrigger every four beats so the resulting sound morphs back and forth between the two waves.
That is just very small taste of the type of manipulation you can achieve using software and, specifically, Absynth. This really just scratches the surface showing how it relates back to the original concepts of subtractive synthesis. Once you get a good command of how things work, there is really no limit to what you can create.
In this last sample, I've loaded up a preset from Absynth that uses all three oscillators, all of the available modifiers and a whole host of envelopes, LFOs and wave morphs. Again, holding down a single middle C generates the following sound.
Conclusion
Synths are a blast no matter how you look at it. 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 now 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 take you a long way.
Most of all ... it's ridiculously fun!