Creating Sound for Synths

1. Sound Synthesis

2. An Outline of Different Wavetypes
• Sine Wave
Most fundamental, basic waveform
Sound at a single frequency
• Square Wave
Many harmonics above their fundamental frequency
Gives off a bright timbre, and are rich in sound due to sharp changes
and discontinuities
• Sawtooth Wave
Similar to a square wave but with harmonic decay and a buzzing sound
• Triangle Wave
Contain only odd number interval harmonics above the fundamental
Produces a soft timbre

3. Subtractive Synthesis
• Most common form of synthesis
Start with a wave form (Such as a sine wave, a square wave, etc…) and remove or
attenuate harmonics associated with it
• Pythagoras
Discovered two strings, pulled to the same tension, sounded great together if their
lengths were related by simple whole numbers.
E.g. If one string was 2/3 the length of another, it sounds good together
• Fourier Analysis
Periodic motion, no matter how complex, can be broken down into harmonic
components
• Different wavelengths define different harmonics
Essentially the same thing
Square wave is a set of harmonics where every other harmonic is present,
sawtooth where every harmonic amplitude is 1/nth of the fundamental, and so on

4. Percussion
• Most percussive instruments do not have
harmonics
Drum pads have more dimensions than a string
(Line), so the sound is different
• Percussive sounds are difficult to create using
synthesis because they are so complex
• Noise generators are good at creating sound of
basic percussive instruments
Noise was the basis for many 90s percussive synths
like the TR808

5. Modifiers and Controllers
• Sound is contoured
In music, static sound is uninteresting
• Envelopes
Defines the loudness of a sound at any given time
Most common is the ADSR envelope generator
• Low-Frequency Oscillators (LFO)
Change a sound and create tremolo
• All synths have a signal generator, modifier (Such
as an ADSR envelope), and controller (Such as an
LFO, which controls modifiers)

6. Filters and Phase Relationships
• Describing wave forms in terms of degrees
In a sine wave, a full cycle is broken down into 4 parts
At the height of the wave, it is 90 degrees, back to zero is 180
degrees, and the bottom of the wave it is 270 degrees, and back to
zero is 360
• Waves can mask and amplify each other depending on time
• Masking on simple waves such as sine waves can result in complete
silence
However, on more complex waves such as sawtooth, it can boost and
attenuate different harmonics
Can lead to a comb filter
• Filters attenuate signals, but also distort it by phase shifting the
harmonics within it

7. Filters and Phase Relationships
• The cutoff frequency of a passive pass filter
isn’t defined by where it starts working, but
where the signal is attenuated by 3db
Dulls the sound, but doesn’t modify the timbre
• The filters in most analogue synths are active
filters
Filters are incredibly complex, and each filter
sounds different than every other one

8. Responses and Resonance
• Potentiometer
Variable resistor
Resistors have an inverse relationship with the cutoff frequency
While most filters in synthesizers are active (I.e. have an
amplifier), the principle remains the same
• Resonance
If an object is excited by sound that coincides with its natural resonant
frequencies, it will vibrate in conjunction with the source of the sound
Every physical object has resonance
• In an active resonant circuit, the frequencies which will be amplified
are the ones near the cutoff frequency
The resonant peak’s width is described by its Q
The lower the Q, the broader the peak
Can create a sweep by using an LFO to sweep the cutoff frequency

9. Responses and Resonance
• As the Q increases, the resonance becomes so
pronounced that the filter begins to oscillate at the
cutoff frequency
• Static Filters can make certain frequencies stand out in
a mix
• Multiple Static Filters can be combined to create
formants in a sound
• As the Q increases, the filter begins to self oscillate at
the point of the cutoff frequency, mimicking resonance
• Filters are the most important part of sound synthesis

10. Envelopes, Gates, and Triggers
• Envelope Generators were originally more accurately called transient
generators
• AD Envelopes can help modify sounds, and when multiple envelopes are
combined, the result can be a polygon shape that is more complex than
what can be obtained by an ADSR envelope (Say, an envelope that attacks,
attacks again, decays, sustains, the attacks again before releasing).
• Analogue Monosynths have three controls when a key is pressed
Pitch CV, which controls the pitch
Trigger, which triggers the transient generator
The Gate, which controls the sustain of the note
The Gate is what tells the synth to continue developing the sound
• Brain uses the first few milliseconds of sound to determine what
instrument is playing
By recreating the initial waveform of an instrument, a sound can give
off the sound of an instrument

11. Envelopes
• The ADSR envelope generator is absolutely
limited when it comes to reproducing sounds
• Different synths are best suited for different
tasks
• Newer synths tend to be better than vintage
ones

12. VCA’s
• The gain of an amplifier is how much louder the
output is than the input
• Volume knob controls how much of the signal
reaches the amplifier
• If sound is amplified too much, clipping and
distortion results
• Using VCA’s, any sound can be distorted using any
other sound
• When using multiple attenuators and amplifiers,
the final gain can be measured by multiplying the
individual gains together

13. Modulation
• Modulation gives life to the signal