- A Brief History
- The Subtractive Method
- Types of Hardware
- Analog VS Digital
- The Subtractive Existential Crisis
- See Also
Synthesizers! That word conjures an image; huge machines covered in switches and knobs, emitting alien sounds and "the EDM." And when you mention the word "synthesizer" to someone, 99 times out of 100 what they will be thinking of is a subtractive synthesizer. But what really are they? And how do they work? Well, my friends, that is what we are here to find out!
A Brief History
The very first synthesizers were "additive." You see, all sound is simply vibration in the air. And, as such, the most simple sound possible is the humble sine wave. By adding together sine waves, you can create all sorts of different sounds! For pitched sounds, these sine waves all line up in a neat harmonic series. And for unpitched sound, the chaos and cacophony of a sine wave mosh pit. Thus, our beloved scientists, seeking to understand sound, crafted machines to add sine waves together. The problem was that complicated sounds would require hundreds of sine waves. Imagine, each waveform requiring its own generator and power. It doesn't take long before you have a machine that is much too large and ludicrously expensive. Then, a new idea! By taking waveforms that already possessed a thick harmonic content, and filtering their frequency range down (SUBTRACTING frequencies), you could create a huge variety of sounds with just a handful of waveform generators. Science triumphs again!
Rise to Prominence
But why even care about a synthesizer? Musicians certainly love having a new or unique sound, but in the early days of subtractive synthesis, these machines would be prohibitively expensive for the working man. So where would the market be? Well, my friends, synthesizers can make all sorts of sounds. And the subtractive synth, as you have most likely heard many times in your life, could make all manner of horn and string sounds. For studios, having a machine around to produce those typical sounds as opposed to needing to bring in a musician and go through the trouble of recording them seems like a no brainer. Besides, it was the future! Listeners would accept these fake sounds, assuming they noticed the discrepancy at all. You add to that all the sound effect possibilities and having the equipment on hand for experimental musicians and studios could see a return on their investment.
Then, the thunderbolt. One can't tell the story of the subtractive synthesizer without mentioning the ubiquitous Minimoog. First released in 1970, the Minimoog took the power of subtractive modular systems the size of bookcases and shrank it down to simple elements that could be fit into a keyboard. Now, live musicians could bring a synthesizer touring with them! More than simply popularizing the subtractive synthesizer with the music industry, the Minimoog would help set the template for all future keyboard synthesizers to come.
A Fall From Grace
Things were going great for the subtractive synthesizer. Disco came and went, and then New Wave came on the scene. It appeared as though the subtractive sound would have a home in any new musical style to come. However, the steady progress of technology would throw a damper on the party. It was in 1983 that Yamaha introduced the DX7, a powerful polyphonic synthesizer that used frequency modulation (technically phase modulation) instead of the subtractive method to generate sounds, and it did this digitally. And while it could prove difficult to program for, it had presets that could really awe the listener in how natural they sounded. At this time, the subtractive synth was still at the height of its popularity, but the DX7 would prove to be the beginning of the end. For polyphonic synthesizers, there were few examples of the subtractive style that were, or in any way, utilizing digital technology. Thus, analog polyphonic synths were much more expensive and less versatile than the DX7.
Yes, most blame the DX7 for killing off the subtractive style, but it was a bit more complicated than that. It wasn't until the late 80s that sampling technology, new digital methods of synthesis, and workstations really drove the final nails into the coffin. Because while these new machines were sometimes capable of the subtractive method, more and more the filter was becoming marginalized. After all, a sampled horn sound would be much more convincing than a subtractive styled one. But beyond the sound quality, these new machines were digital, lighter, more powerful, and cheaper. It was then a matter of image, the subtractive synthesizer being seen as a wholly analog one; those bulky units that were prone to failure. Just like that, the star had fallen for the subtractive beasts of yore. And as far as the world could care, those wood paneled, cigarette smelling, clunky looking, Disco loving dinosaurs could get fucked.
Survival in the Underground
Now good and well out of vogue, people were practically giving away old subtractive synthesizers. Heavy, walls of modular units gifted to whoever would truck them out of the way. Our subtractive synths were left homeless, crying on the streets. But while the streets can be brutal, those with real heart can find a place to thrive. For it was here that the bargain priced subtractive machines found their new home, the low budget producers of the club scene. The awesome, room shaking power of the analog synthesizer proved to be desirable on its own merits. Certain units even went from being cult classics to cultural icons. The Roland TB-303, for example: a cheesy bass sequencer meant to accompany practicing guitarists would end up crafting whole sub-genres of electronic music all by itself. The samplers and workstations were here in the club scene as well, but they all worked in harmony. A blissful, drugged out stupor on the dance floor.
The subtractive synth had regained some traction in this place. So much so, that in the late 90s and early 2000s, companies had begun to take notice. New synthesizers billed as "virtual analog" or "analog modeling" were produced. These weren't simply digital synths using the subtractive method, but machines meant to completely mimic the workflow of older analog units, right down to the nomenclature of their front panels. Because as the older units began to fail or disappear, and as collectors began to horde, vintage machines were becoming harder to come by (and skyrocketing in price). The subtractive fever had began to spread again.
It was as the 2000s rolled into the 2010s that the perfect storm coalesced to bring the subtractive style back into prominence. The club scene and electronic music in general that had held steady through the 90s proved the subtractive sound had its place. And the 80s aesthetic was suddenly becoming chic again, a time when the subtractive sound was all the rage. Beyond that, the line between what was club music and what was popular music was beginning to blur. Perhaps somewhere, a brilliant producer realized they could make twice as much money if their songs got play in the clubs and
on the radios. And the analog machines that so defined the subtractive methods were suddenly the coolest things around. "Oh no," the people thought, "it turns out that Disco WAS cool! And that it was Metallica that sucked all along! How could we have been such fools? And actually, we always knew this. It was everyone else that was stupid."
With the legendary subtractive machines put on a pedestal, software developers tried to create virtual machines to closely mimic them. But digital software could never be a spot on replication of the real deal. Manufacturers couldn't ignore this hungry market, and new subtractive hardware began to be produced. People demanded analog legitimacy, and now, they could have it. Vintage units were mimicked or re-issued, and completely new machines were created. It was a new golden age for the subtractive synthesizer. And this time, they seem here to stay!
The Subtractive Method
"The subtractive synthesizer takes a complex waveform and filters it down to create new sounds. Wow, that was easy! Why did I bother reading all that history nonsense?" This, you are surely thinking right about now. But knowing the basic format and what each element does will help focus your foray into the subtractive world. Much like lovemaking, a familiarity with each part will lead to better results than haphazardly turning knobs and flipping switches. It is now time for your education. Please pay close attention to each of these elements.
Probably the most critical part of your subtractive synth, the oscillator is what generates the actual sound! Think of the oscillator as being the vibrating string of a violin, or the membrane struck on the head of a drum. There are a few waveforms you will find typical on the subtractive synth, as in the early days of analog equipment, these were easy to generate via electricity. The sawtooth ( /| ), the square or pulse ( _| ), the triangle ( /\ ), and the sine wave ( "S" but on its side). You may also see white (or other colors) of noise available with your waveform selections or having its own dedicated generator. Each waveform has its own characteristic sound which would be difficult to describe here with words. Simply know that you will see these frequently, and you should familiarize yourself with their timbral uses.
Types of Oscillator
The format and style of oscillator can obviously change depending on the machine you are using. These are the most common you will come across.
The Voltage Controlled Oscillator is just that, an oscillator having its pitch directly controlled by electric voltage. Please note that digital and software synths will frequently label their oscillators as VCOs just to stay in line with the format, this label will not inherently mean your synth is analog. The benefits of real VCOs is their strength and full resolution that comes with the power of being driven directly by electricity. The biggest drawback is their penchant for pitch drifting. Keeping old analog gear in tune could be a difficult task, and it was a primary reason as to why they fell out of favor in the first place. On the other hand, the unpredictable nature of pitch drift in VCOs gives them an almost organic charm that simply can't be replicated by other means.
A Digitally Controlled Oscillator is, contrary to some belief, not a completely digital affair. It is, in fact, digital control of an analog oscillator. The benefit of this digital control was that it helped increase the pitch tuning significantly. This was the most useful in polyphonic synthesizers where multiple voices needed to sound in tune with each other. The drawback of DCOs is that they can sound a little stiff and lifeless when compared to VCOs, yet won't have the perfect tuning that a completely digital generated sound can.
Wavetables and ROMplers
These are completely digitally generated waveforms. Wavetable oscillators are a series of single cycle waveforms set in a table. These multiple waveshapes can be swept through smoothly for interesting new timbres. "ROMpler" was a somewhat derisive name used to describe single cycle and larger samples that would be played back as the oscillator. Generally, these multiple samples would be less smooth than wavetables. Wavetable synthesizers would typically employ much more complicated waveshapes than the standard subtractive fare, while ROMplers may have complex orchestral hits and drum sounds available.
Something of a new buzzword, NCO is typically used for a digitally generated waveform that is produced at such a high resolution as to be indistinguishable to a real VCO. The benefits are obvious, digital components are much less likely to fail, and pitch can be kept as stable or unstable as the user desires. Of course, for some, only a true Voltage Controlled Oscillator will do.
Simply having a single oscillator is nice, but more is (almost) always better. When a synth possesses multiple oscillators, it will typically label them as OSC or VCO 1, OSC 2, ect... What this means is that each available voice of your synth (1 if monophonic, more if polyphonic) will have this number of oscillators available. More oscillators will give you a thicker spectrum of sound. Common usage of multiple oscillators includes having a slight detune to create phasing of the voice or having oscillators set to a specific tonal interval, such as an octave or 5th. Multiple oscillators can also have modulation interplay between each other, such as FM or ringmod effects. You may also come across Sub Oscillators. These will typically be set to 1 or 2 octaves below you pitch input, and be less versatile than a full fledged oscillator, lacking modulation or other effects.
Here we have the element that makes the subtractive synth truly subtractive, the filter. The filter removes (rather, filters out) certain frequency content of the sound. This changes its very nature. But what is most key to the subtractive synth "sound" is not simply that it has a filter, but that it has a "resonant" filter. The resonance or "Q factor" creates a boost in the frequency right at the point where the filter cutoff begins. Think of it like boosting a certain band on an EQ, but much more focused and pointed. It is a crucial element in giving the user more control over shaping the sound. Beyond that, the resonant filter is the hallmark of the subtractive method. The motion of a resonant filter doing what can best be described as the "wet fart" sound you have probably heard many times before. So, to further emphasize, here are the two most important controls you will have on your filter.
The control you will see labeled cutoff is what sets the location on the frequency spectrum where the filter begins removing sound. Creating motion in this cutoff setting, via an envelope or LFO or even direct control, is a typical tool used in the subtractive method.
This control will increase the amount of boost or spike at the frequency cutoff point. More resonance generally means a more aggressive or sharp sound, but some filter models can lose volume when the resonance is cranked. Some filters are capable of so much resonance that they can self oscillate, the spike in frequency overpowering the whole signal to generate its own tone. This will result in an electronic "whistling" type of sound you may recognize.
Analog and Digital
As with oscillators, filters can be either analog or digital in nature. The analog filter using electronic components while the digital one processes its signal with code and numbers. Just because something is labeled VCF does not mean it will technically be a "Voltage" Controlled Filter. And as with oscillators, digital filters will not have the resolution or drifting character you will find with a truly analog one. On the other hand, digital filters can be capable of more complicated filter modes, such as the comb filter.
Types of Filter
While they all do the same basic thing, the fundamental cutoff ramps and types of filters can vary widely. Here are the different types of filter you will come across.
The Low Pass Filter is by far the most common type of filter to be found in the subtractive method. It cuts off the high frequencies of the sound (allowing the low signals to pass through). If you want the most typical types of subtractive sound, you will want to go with the LPF. It is particularly useful for creating thick and rich sounding basses.
The High Pass Filter works as the opposite of the LPF, it cuts off the low frequencies while maintaining the highs. For some vintage polyphonic synthesizers, it is not uncommon to have a non-resonant HPF in the signal chain after its LPF. This could keep big chords and multiple voices from becoming too muddy or overpowering. Indeed, the HPF is most useful for thinning out your timbres.
The Band Pass Filter works like a combination of the previous two, cutting off both high and low frequencies! You may find the BPF a bit more difficult create natural sounds with, but it excels at creating notes that are thin and pointed.
The Notch/Band Reject Filter
Finally, this acts as the inversion of the BPF. The Notch filter removes the specific frequencies around the cut off point. And like the BPF, it can be more difficult to find uses for the Notch filter. Results can vary widely depending on the pitches (see: frequencies) of the oscillators going through it.
Now that we understand where the frequency is cut, we can learn about how it is cut. A typical filter you may find will be a 4 pole-24db/oct LPF. The 24 decibels per octave refers to how sharply the frequencies are filtered out. As you may see in graphical form around your filter, there is a slope or ramp from full volume to no volume as you go past the cut off point. Now you may also find a 2 pole-12db/oct LPF. This means that slope is half as sharp as the 4 pole variant. A 3 pole filter will be 18db/oct, 1 will be 6db/oct, ect... What this means practically is that more poles means sharper cut off means less harmonic content remaining in your final sound.
For our older, analog subtractive synthesizers, the oscillators would always be "on" as long as the machine was on. Of course, a piano should not constantly be having its keys struck when not in use. Thus, it was required that the audio be fed through a Voltage Controlled Amplifier. This allowed for a specific volume level to be set for the sound. But having sounds be simply ON or OFF (see: gated) would not result in voices that were anything near to being natural. This is what necessitated the need for the envelope, something that could control the shape of the volume.
The Envelope Generator creates a shaped signal used to control other elements in the synthesizer. For the above mentioned VCA, for instance, it will create a rise and fall in the volume level that will be more in line with how acoustic instruments work. Imagine striking a drum, there is a loud crash and thump, and the sound slowly fades away as the drum stops vibrating and the sound stops reverberating in your space. For this purpose, envelopes almost exclusively work with adding positive values to what they are changing, but you may occasionally find envelopes with the ability to be flipped and go negative. You might also come across looping envelopes, which are more in line with what we will discuss later, the LFO.
While there are a huge variety in the types of shapes you can find in envelope generators, I will only be discussing by far the most frequently used: the ADSR. When describing how each stage works, I will be using it manipulating the VCA for example. This is because it should provide you the most clarity for how the envelope is manipulating a parameter, as well as being almost constantly used for that purpose. But the EG can certainly be used to change other sections of the synth, most common of which being the cutoff.
Furthermore, I will be describing these stages how they function in the context of a keyboard. When a key is struck, the envelope will be triggered (initiated). Just be aware that there are EGs out of the context of the keyboard format, and that they can be used in more complicated ways.
The ADSR Envelope
The Attack controls how long it takes for the envelope to reach its maximum value. A short attack means it will happen almost instantly, while a long attack means it will slowly creep to the top. As related to the VCA, a short attack creates a sharp spike in volume such as the striking of a piano key, while the long attack is more like a vocalist slowly ramping up in a crescendo.
After the attack stage has finished, the level will Decay until it has reached the level set by the Sustain. And like the attack, the Decay parameter simply controls the amount of time it takes to achieve the next stage. Again, in relation to volume, a short decay will behave like a plucked string, while the long decay is more akin to a struck gong, slowly fading away.
The Sustain sets the level the envelope will hold at until the corresponding key is released. For volume, let us imagine pressing a key on a piano. As long as the key is held, the string is allowed to vibrate. However, this isn't a perfect comparison. For the string of a piano will stop vibrating eventually, but our electronically powered synthesizer can maintain its voice indefinitely.
The Release, much like attack and decay, is a time related setting. It controls how fast or slow the level of the envelope will return to zero once, the key on your synthesizer has stopped being pressed. Note that, if your sustain is set to zero, the decay and release are performing a similar function. This could allow you to essentially have "two" releases, a different style whether the key is being held or quickly tapped.
Now we have all the basic building blocks for our subtractive sound: the oscillator to produce the sound, the filter to color it, the amplifier to give us control of the volume, and the envelope to provide a somewhat natural shape to the above mentioned. But by simply using these elements, you may find your sound to be completely dull and lifeless. That, my friends, is where the LFO comes in!
The LFO is a Low Frequency Oscillator. For our older analog subtractive synths, these oscillators were generated in the same way as their audio oscillators were; thus, they were capable of the same familiar shapes.
So why low frequency? As a pitch goes higher, when speaking in terms of a single cycle waveform or anything else, the cycles of waveforms goes by faster (see: more frequently). And lower, they go by slower. Keep going lower in frequency, and you will eventually have something moving so slow that it is not audible. However, the purpose of the LFO is not to be heard directly, but to be used as modulation. Think of the LFO as being MIDI automation before MIDI, constantly changing the settings of other elements in our synth.
Let us use a triangle wave ( /\ ) for our example. Imagine a triangle wave LFO is being used to manipulate the pitch. As our analog gear is using alternating current, the triangle wave is going up and down, providing a signal moving from positive to negative. Therefore, our pitch is going both up and down. This effect you may commonly know as "vibrato," and can be easily seen when a violinist is wiggling their finger on the finger board to quickly alter the pitch of their note. Now that we know what our LFO is doing, let us look at its common two parameters.
This controls the speed (rather, frequency) of our LFO. Try to hear the vibrato of our above mentioned example. As you turn the knob to increase the rate, hear the vibrato going faster and faster. Turn it down and hear it go more slowly, eventually going so slow that you can barely notice it. Turn it back up again, and it starts getting really fast. Keep going up, and what happens? It creates a strange mess that is no longer vibrato! What has happened here, is that our LFO is no longer oscillating at a low frequency, it has gone into audio rate. You will notice that once you have entered the realm of "audio rate" modulation, your sounds will have a very metallic quality to them. The frequency modulation used by the DX7, for instance, is all audio rate modulation.
Be aware that how fast and slow the predetermined LFO can go is dependant on the hardware you are using. Not all LFOs are set up to go into audio rate.
The Depth controls how much modulation or change is being applied to the destination. It is essentially a VCA controlling the level of the effect between the LFO (source) and its destination. Thinking back to our vibrato example, very little depth will create a change of pitch that is hardly noticeable. Crank the Depth, and now our pitch could be sweeping a whole octave up and down! And as with the Rate, how much Depth you have available to you is completely dependent on how your hardware is set up.
Other Terms and Elements
The above was the most common facets of the subtractive method, but here are a few other terms and abbreviation you may run across.
CV: CV is Control Voltage. Before MIDI, our VCOs needed to be controlled somehow. Thus, the CV is what controls the pitch of our oscillators. It has steadily become more common for modern analog hardware to posses CV functionality to better integrate with older equipment.
Gate/Trigger: As the Control Voltage gives us our pitch, the Gate or Trigger is what signals when a key has been pressed. These terms can be used interchangeably, but Gate is most appropriate to use when referring to a keyboard controller (the gate is "open" while the key is pressed and "closed" when it is released) and Trigger more applicable in the context of drum machines where each instrument/voice is triggered once and not sustained.
Sync: When you have multiple oscillators, it may be possible to synchronize one to another. This means that their frequencies will be locked to match. How is this useful? Well, when one oscillator is tuned different from the other, their frequencies will obviously not match. So when Sync'd in this situation, the waveform is essentially being snipped so that it matches the other. For older analog machines, this was an easy way to get new waveshapes out of the more simple ones available. Try modulating the pitch of one oscillator in a Sync situation for aggressive sounds!
Keytracking: With a keyboard, you may have access to this powerful modulator. The keytracking can alter the values of parameters (such as filter cutoff) depending on how high or low on the keybed you are playing.
Velocity: Another keyboard related modulator, and one you may be familiar with outside of the context of subtractive synths. The velocity modulates your notes depending on how fast a key is pressed. This is most typically applied to the VCA or VCF.
Mod Wheel: Also a term that lives outside of the subtractive method. In context of our synth, the Mod Wheel can be set to control any number of parameter values. Its purpose is as a performance related one, allowing a player fast and easy manipulation of the aforementioned values.
Patches: For old modular units, the entirety of the subtractive elements needed to be wired (patched) together with cables. This lead to sounds generally being referred to as "patches." The name endured, and sound patches refer to parameter values that have been saved to your synth's memory.
Effects: More common with digital hardware, a subtractive synth may have its own effects available on the unit. These will be the typical audio effects you may be aware of, such as delay and chorus.
Types of Hardware
Subtractive synthesizers can come in many shapes and sizes, but these are the primary groups you will come across.
What we have used as our primary example and what you should be most familiar with. The keyboard will include, obviously, a keyboard, as well as controls to adjust the parameters of our subtractive elements. These controls may be numerous or minimal, and come as a variety of knobs, faders, and switches.
A self enclosed synthesizer that has all the elements and controls, but removes the keyboard part. Modules began as being an almost exclusively digital piece of equipment (The TB-303 being a notable outlier), but have grown to prominence in the space starved current market with both virtual and real analog subtractive synthesizers.
The standardized studio rack mounts are most frequently used for effects, but sound generators are also widely available. For a subtractive synth, the amount of controls on the face of a rack mount unit will be limited simply given the slim form factor of these units. With the wide number of parameters in the subtractive method, this can make editing difficult in rack units.
As mentioned before, the first subtractive synthesizers were modular. Each of their elements (VCOs, VCAs, ect...) enclosed in their own self contained unit. These synths were expensive, after all, and this allowed buyers to only get as much as they needed or were able to afford. Each unit would need to be manually wired together for the electric signal (sound, in this case) to pass completely through.
Recently, the "Eurorack" modular style has seen growing popularity. Eurorack is a standardized format for power supplies and control voltages allowing different manufacturers to create subtractive elements that can all work together. But remember that before you start purchasing the different elements you have learned about above, you first need a case and compliant power supply to house your dream synth.
Now that we understand how our subtractive synthesizer functions, it is important to talk about polyphony. Polyphony refers to how many notes your device is capable of sounding simultaneously. For a piano, the polyphony will be equal to how many keys it has; each key possessing its own string to be struck. That isn't going to be practical for our subtractive method, however, with each element requiring so many electric components. Therefore, we have certain types of synths produced for different purposes.
A monophonic synthesizer is capable of producing one note at a time. It was the original subtractive type and still the most common. As mono synths only have once voice to produce, they typically have more oscillators and elements than units with more polyphony. Thus, they are typically capable of more powerful and complicated sounds.
A polyphonic synthesizer is capable of producing multiple, independent voices. Think about having multiple monosynths side by side, and then cramming them together into one unit. The amount of notes it can produce, or "polyphony," is dependent on the hardware. You will find four, six, and eight voice polys to be the post typical. As each voice requires its own individual elements, polyphonic synthesizers will generally have less oscillators and elements than a monosynth. This makes their sound less powerful and complex, but that is usually welcomed to keep the multiple voices from creating unclear sound.
A paraphonic synthesizer is capable of playing multiple notes, but does not have separate elements for each voice. For example: a monosynth with two oscillators that can play each independently might be called duo-phonic. The two oscillators are separate, but there still remains only one VCA. Each time a new note is struck, the EG will be retriggered. Therefore, a paraphonic synthesizer may be capable of multiple notes, but noodling away on the keyboard will create a chunky effect of constant triggering.
Analog VS Digital
As discussed in the history section, the subtractive method has become ingrained as an inherently analog one. However, there is nothing about this method that necessitates it be as such. There is a vast amount of digital synthesizers, both hardware and software, that use the subtractive method. It is just important to reiterate that wile the analog appropriate names for the elements are almost always used, that does not necessarily mean you are dealing with a truly analog piece of equipment.
In regards to sound, novels worth of debate are available elsewhere. True analog gear, while infinitely more accessible now than it ever was, is still incredibly expensive. On the other side, you may find many good sounding software subtractive synths available for free. The merits of the former and the proficiency of the latter are ultimately up to you to decide for yourself. But it would be complete folly to try to make this sort of decision before you have been familiarized and have gained sufficient experience in the subtractive method as a whole.
The Subtractive Existential Crisis
When first learning subtractive synthesis, it can seem quite daunting. However, once one has used these tools for a sufficient amount of time, the restraints are obvious. The minute differences of oscillators and filters between units can begin to blur into sameness. You may become bored with your mastery of the subtractive method, irritated over arguments about which unit is superior when they all are doing the same basic thing. Don't be alarmed, this is a crossroads most will come upon.
I will simply posit that the subtractive "sound" is something that has now well established itself in our musical lexicon. Think of the subtractive synth as its own family of instruments, such as brass or woodwinds. Some might argue that there have been no advancements or innovation in the subtractive method in this current decade, but I would ask them where has the innovation been for the violin in the past centuries.
So, do not cast aside the subtractive method as simple fad or unnecessarily stifling constraints, but as another tone for your compositional palette. And enjoy this golden age of the subtractive revival!
The excellent "Intro to Synthesis" series of videos