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Synthesize

How does it work?

A musical synthesizer is an instrument that uses electricity to make musical sounds.

  • When playing a synthesizer keyboard, sounds are made by turning electrical oscillators on and off.
  • the raw electrical signal is modified by the configuration of the synthesizer.

A synthesizer has all the necessary properties to create "any" sound. It can

  • Generate sound waves of different shapes.
  • Generate more than one sound tone at once to produce a fundamental frequency and harmonics.
  • Make the volume of the sound change over time to produce different sound envelope shapes (ie. attack, decay, sustain, release).

To do this, the synthesizer has a number of different voices or oscillators (sound tone generators), each of which can produce waves of different shapes (sine wave, square wave, saw tooth, triangular wave, and so on)

  • these waves can be combined to make complex sounds

Sounds on a synthesizer can be made in either an additive or subtractive way

  • anal: consider that art can be made by combining different elements (additive), or it can be made by removing the parts that don't belong, like a block of marble (subtractive)
  • the subtractive method is much more common, meaning we start with a complex sound, filter it to remove harmonics, and envelope shape its volume.

Modulation refers to how the sound of the synth changes

  • ex. one way to modulate the sound is by manipulating the pitch envelope. another way is to adding an LFO.

Subtractive Synthesis (most common)

Subtractive synthesis is so-called because the approach is to take a raw soundwave sound, and alter its timbre by applying a filter.

a simple subtractive synthesizer makes sound using four independent components:

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

Analogy: human voice

When a human sings, the vocal folds act as an oscillator, while the mouth and throat act as a filter.

  • consider that singing "aaah" has most of the original harmonics still present, but as we switch from "aaah" to "oooh", a lot of these harmonics are removed. In both cases, the sound generated by the vocal folds is more or less that same. It is the mouth (ie. the filter) that is responsible for altering the sound.
    • note: by going back and forth between "oooh" and "aaah", the human voice is able to create a spectral glide (ie. a sweeping filter), similar to a wah-wah

Envelope

An envelope shapes the sound in a certain way, depending on the type of envelope it is.

  • ex. If it is an amplitude envelope, then it shapes how the sound's amplitude changes over time. If it is

In the case of an amplitude envelope, the envelope tells the amplitude how to behave from the moment the key is pressed, to the moment it is released (and after; ie. release)

In the case of a filter envelope, the envelope determines the frequency content of the sound by using the cutoff and resonance controls.

Filter Envelope Analogy: Human voice

consider the human voice going from "oooh" to "aaah".

  • A fast attack here would mean changing from "oooh" to "aaah" quickly.
  • Decay would determine how long we stay at the absolute "aaah" position. A short (quick) amount of decay would mean we arrive at the sustain level shortly after hitting the absolute "aaah" position.
    • ex. think of the Tom Sawyer intro how it moves from that open mouth position to that closed mouth position.
  • Sustain would determine how much we close our mouth from the absolute "aaah" position. A lot of sustain would mean we barely close our mouth, while little sustain would mean we return very close to the "oooh" position.
  • Release would determine how quickly we return to the initial "oooh" position.

you might have an envelope for pitch, one for amplitude

Oscillator

In a synth, the oscillator produces the source of our sound (square wave, sawtooth wave, etc.)

  • different wave shapes produce different timbres

An oscillator is something that "vibrates", or repeats the same pattern.

  • ex. The pendulum of a clock, albeit a very slow oscillator.
  • ex. A piano string "oscillates" when struck by a hammer.
  • Electric oscillators might be made using transistors. They turn electricity into electrical patterns, or signals, that repeat over and over. When different keys are pressed, different notes are heard. This is done by making the signal from the oscillator repeat at different rates.
  • To get any sound, first we need a source. The most common source is a VCO (Voltage Controlled Oscillator)

An Oscillator makes a periodic signal, which can be listened to as a note or used to apply parameters to other synths, filters, etc. as a periodic signal

anal: imagine an oscillator as a speaker on a carousel, while you are standing on the side

Doubling

Often, we want to combine 2 different oscillators into one. We can do this with a mix knob to bring the sounds together

  • this second oscillator might produce a unison sound, an octave, a harmonic interval etc.
  • most often we want to push the mix knob toward the lower pitched oscillator
    • ex. if osc2 is at an octave higher than osc1, then we might put the mix knob at 70% osc1 and 30% osc2 in order to make a more cohesive sound. Otherwise, we find that the higher pitched oscillator dominates a little too much.

LFO (Low Frequency Oscillator)

You can think of LFOs as robots that make a repeating change to some aspect of the sound.

An LFO is an oscillator that oscillates at 20Hz or less. It's particularly useful because it makes a fun modulation on stuff (wobwob) among other things It sounds cool, and might not have a high enough frequency to be heard by the human ear.

  • ex. an LFO might control how loud and soft the signal is, or control the pitch of the signal
  • ex. An LFO might even control the actions of the filters.

note: Don't confuse low frequency with meaning low pitch. While low pitches are indeed created by vibrating at low frequencies (the open E of the bass is about 41Hz), an LFO is not creating any sort of pitch for you to hear. It's using this low frequency in a different way.

Params

Speed

Controls the rate (frequency) at which the LFO loops

Amount

Controls how flat/bumpy the LFO wave is

Pulse width

Allows us to change the shape of the waveform.

  • in its default state, it is simply a square wave

The pulse wave has a sort of artificial videogame-like quality to it.

Pulse width goes from thin (leftmost) -> medium -> square (rightmost)

At high pitches and with a thin pulse knob, a pulse wave sounds similar to a saw wave

The pulse width knob doesn't affect any other type of wave; only pulse waves

  • Pulse width may be named "symmetry", in which case it will also affect other waveforms

https://learningsynths.ableton.com/en/oscillators/pulse-width

Filters

A filter behaves a bit like a wall or door. It lets some parts of the sound through and makes other parts quieter.

  • anal: think of how music sounds while you are standing outside the room. It sounds muffled, since the walls are filtering out some frequencies. Now, when you open the door to the room, the music becomes less muffled, since those previously filtered frequencies can now be heard.

A synth's filter is like a fingerprint— they all seem similar at first, but there are subtle differences that play a big part in determining the synth's character.

Low pass filter is by far the most common type of filter

Cutoff frequency

Controls the brightness of the sound (ie. the frequency at which sounds will be allowed to pass)

  • therefore, if we were going for a sound more reminiscent of a bass guitar, we'd turn this knob down quite a bit

Controlled with the cutoff knob

  • note: turning this knob down also reduces the volume of the patch, so we'll have to compensate by increasing the master volume of the synth.

Lower cutoff values make it more difficult to hear the characteristic differences between different waveforms.

Resonance

Increases the amplitude around the cutoff frequency

Achieving different synth types

These are general guideline tips that should be thought of as starting points more than anything else.

Pads

Characterized by slow amp attack and release times.

They also normally have a low cutoff, creating a dark and round sound that allows the pad to blend more into the background

Lead

Characterized by high cutoff value

Very quick amp attack

Bass

Characterized by a low cutoff value.

The square wave has a natural low end, which can be utilized to great effect when making a bass patch

Very quick amp attack

A waveform is the raw sound that a synth generates

  • the waveform is generated by the oscillator

UE Resources

E Resources