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  • Ryan van Eerde

A Lesson in Subtraction

Updated: Oct 16, 2018

Making sound with subtractive synthesis


Creating sound (sometimes noise) with synthesizers is not a particularly difficult thing, the difficult part is making something that sounds good that can be used effectively in a piece of music.


What exactly is subtractive synthesis, simply put its the process of removing or filtering out harmonic overtones of a sound usually from oscillators or signal generators to create and shape a new sound. There are a few components that are used in this process to make, craft and shape the desired sound.


Firstly and the main source of the sound is from an oscillator which produces a number of waveform shapes such as, sine, triangle, square, sawtooth, and noise, each waveform has a different sound and frequency/harmonic content with their pitches being determined by the frequency of the oscillation (an oscillation at 440Hz would produce an A note).


Visual representation of the different waveforms and their harmonic content

Most of the time the pitch or note being played is determined by MIDI information, assuming you are using virtual synths in a DAW, inputting a C Midi note will will cause the synth to play a C. Another cool thing you can do with virtual synths is that you can transpose the inputted MIDI note information up or down in semitones or in smaller fine tuning increments to layer different pitched harmonics together.


Below is an image of a synth plugin in Ableton Live, it has 4 synths each with their own pitch adjusting parameters, Coarse meaning whole Octaves and Fine being smaller tuning increments.



After the oscillator, the signal can be sent to and controlled by filters, envelope generators, modulators and amplifiers. The amplifier is self explanatory, it controls the overall output volume of the synth, which can be controlled and manipulated to create certain effects, more about that later though.


Filters are essentially just equalisers and are used to sculpt out unwanted frequencies and/or boost wanted harmonics, the most typically used filters are high-pass, low-pass, band-reject, and band pass.


Different types of EQ filtering

Envelope generators are used to shape the amplification of an oscillator with and are typically called ADSR's due to there 4 parameters, Attack, Decay, ,Sustain, and Release. Attack determines how quickly a note will reach its full level, fast attack means the note will be heard instantly where a slower attack the note will swell and steadily increase to its full level. Decay is how long the the waveform takes to reach the Sustain which is the audio level after the initially Attack, then lastly the release is how long the audio takes to drop off from the Sustain level to nothing.



ADSR envelope

The last main component is modulators with the most common being the Low Frequency Oscillator or LFO. It works like a normal oscillator with the ability to change what waveform it produces and what frequency it can oscillate at, but instead of producing sound it is used manipulate other aspects of the synth. Depending on the synth the LFO can be assigned to control multiple parameters such as the Amplifier output, oscillator pitch, filter frequency, just to name a few. A good example is the Amplifier output, the LFO can be used to control the volume up and down to produce a pulsing effect.

The amount of oscillators being used and how they are mixed together with these other processes have the potential to create a myriad of vastly different sounds with different tonal textures.


As I don’t have much experience working with synths it was greatly beneficial learning about them and how all the separate components work together, to get hands on with working out synth sounds I used the Operator synth plugin in Ableton.



Ableton Operator Synth

It's a very simple plugin consisting of only a few components, which are 4 oscillators with the ability of producing multiple wave shapes with their own independent ADSR envelope generators, and modulation and filter controls for the master output.


In my reference track there is a sawering (not sure if that's a word or not) synth pad tone that I wanted to recreate for my own project in one of the melodic sections (Melodic Synth 2), so I used Operator to try and come as close to that sound as I can. I re-wired Ableton into Pro Tools so I could bounce down the Midi sounds to audio files, and I’m also just more familiar with Pro Tools. I also used a couple other Midi tracks from my session to give better context to the sound I created.



Ableton ReWire into Pro Tools with Midi Information

The first thing I hear in the Killer Instinct synth tone is that it’s layered with multiple oscillator pitches, Operator as 4 oscillator to choose from so I put a couple of them up a few octaves. I knew that the sound was based around the saw waveform so I experimented with different saw oscillators to get a couple that fitted together. Another thing that stood out to me was there was definite noise sounds that can be heard on the attack of each note so I used a white noise wave to get that effect. Lastly I also used a square wave to get a buzzy distorted sound, and from there I began blending the 4 different oscillators together.


From here I started working on the ADSR settings of each oscillator, the sound on the Killer Instinct track cuts away relatively quickly so I knew that my decay and release times had to be quite short, also there isn't much of an initial attack in the sounds either to the attack settings would have to be a little bit longer. With these parameters in mind I began experimenting again and fine tuning the ADSR setting until I felt the sound was getting close.

ADSR envelope of oscillator A

I then used the spread function next which creates a chorus effect to widen the stereo field, I did this because the reference tracks sound is not right in the center. I then fine tuned the pitch of 3 oscillators to increase the width of the sound even more. Next I engaged a notch filter a sweeped around the frequency spectrum until I reached a point that had the right resonance and feel, what I liked about the filter was that I could click on a graph and move it around freely which made finding the right frequency easy. I also moved the phase of oscillators A and B to create another frequency filtering effect.

Graphic Filter Settings

Lastly I incorporated an LFO that affects the tone of the oscillators, with a bit of playing around I thought it sounded the best being used on only oscillator B and C, I used a fairly high oscillator rate to match the tempo of the song and blended in the amount until it reached the tone I wanted. I then just experimented with the other Midi tracks to try and discover what other sounds/tones can be made and broaden my synth creating abilities.


See link for Pro Tools & Ableton session download

https://drive.google.com/open?id=1SrjJPQWf24jDF__nqu1414zKKJS1A3RG



References

Sound Design Basics: Subtractive Synthesis. (2018). Retrieved from https://cymatics.fm/blog/subtractive-synthesis/


What is Subtractive Synthesis? - The Only Explanation You'll Need. (2018). Retrieved from https://musicproductionnerds.com/what-is-subtractive-synthesis


Jones, A., & Cousins, M. (2018). Ableton Live Tutorial: Bass Design With Operator - MusicTech. Retrieved from https://www.musictech.net/2013/07/ableton-live-tutorial-operator/

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