Introduction to synthesis

Question 1

What are the three stages of a typical synth?

Answer 1

Oscillator, Filter, Amplifier

Question 2

Describe the Oscillator.

Answer 2

Signal Generator
 (creates the wave – sine, saw, etc.)

Question 3

Describe the Filter.

Answer 3

Change Frequency Content
 (LPF, HPF, BPF, Slope, Resonance, etc.)

Question 4

Describe the Amplifier.

Answer 4

Change Amplitude
 (i.e. varied over time – envelopes, etc.)

Question 5

As well as signal generators, what can oscillators be used as?

Answer 5

Signal modulators – used to control a variable
 (e.g. low-frequency oscillators, or LFOs)

Question 6

How can oscillators be combined?

Answer 6

• Additive synthesis adds sine waves together
 (as harmonics or partials) to build up complex tones.
• Subtractive synthesis uses complex tones to generate many harmonics, which are then filtered.

Question 7

How do analogue synths add richness to a synth voice?

Answer 7

Combining several types
 of wave together.

Question 8

Describe the audio signal and LFO of a sine wave.

Answer 8

Audio signal = pure, flute like

LFO = gentle, and/or gradual change

Question 9

Describe the audio signal and LFO of a sawtooth wave.

Answer 9

Audio signal = buzzy, nasal quality

LFO = falling attack (rising reverse-attack) shapes

Question 10

Describe the audio signal and LFO of a pulse/square wave.

Answer 10

Audio signal = square: hollow, clarinet-like, sometimes buzzy. pulse: varies from hollow to thin.
LFO = alternates between two states (a high value and a low value) - also useful as trigger signals.

Question 11

Describe the audio signal and LFO of a triangle wave.

Answer 11

Audio signal = hollow like a square wave but less bright

LFO = Gentle and/or gradual change but sharper changes than sine at maximum and minimum

Question 12

Describe the audio signal and LFO of noise.

Answer 12

Audio signal = ‘sss’ sound (white noise), ‘shh’ sound (pink noise).
LFO = random variations of a setting.

Question 13

What do filters modify?

Answer 13

Filters modify the frequency characteristic of a input signal – adding to, or taking away from, a range of frequencies within the overall sound

Question 14

What are filters the basis of?

Answer 14

Subtractive synthesis

Question 15

What does the cutoff frequency in a LPF and HPF define?

Answer 15

What ‘high’ and ‘low’ frequencies are filtered. The cutoff is defined as where the amplitude has fallen by 3dB.

Question 16

What are shelving filters used to alter?

Answer 16

• High and low shelving filters used to alter 
high and low frequencies respectively
• They either boost or cut some of the signal
  (most “bass” and “treble” controls are of this type)

Question 17

What do band pass filters allow?

Answer 17

Band-Pass Filters allow a band of frequencies through around a centre frequency (Fc)

Question 18

What do band-stop filters stop?

Answer 18

Band-Stop (or Band Elimination, or Band Reject) Filters similarly remove a band of frequencies

Question 19

What do peaking/notch filters do?

Answer 19

Peaking (or notch) filters boost (or cut) around a centre frequency, without cutting other frequencies.
The “sharpness” of the filter is defined by the Q factor. High values of Q are sharper.

Question 20

How are amplifiers used in synthesisers?

Answer 20

In synthesisers, amplifiers are used to make a sound more interesting by varying amplitude over time.

Question 21

What part of an oscillator does an LFO control?

Answer 21

Frequency (pitch) - (like Vibrato, where violinists rock the finger to waver pitch)

Question 22

What part of a filter does an LFO control?

Answer 22

cutoff frequency - (like Wah-wah, on guitars or the human voice)

Question 23

What part of an amplifier does an LFO control?

Answer 23

gain (like Tremolo, where woodwind players vary breath strength).

Question 24

What do envelopes control?

Answer 24

They control the change of a parameter over time (e.g. amplitude, frequency, filter)

Question 25

How are envelopes different to oscillators?

Answer 25

Unlike oscillators, which are periodic and never actually start or end (they repeat), envelopes have a start and an end, but can have looped sections.

Question 26

What does an amplitude envelope represent?

Answer 26

An amplitude envelope simply represents the way in which the overall level of a sound (e.g. a note) varies over time ..

Question 27

Describe a pitch envelope.

Answer 27

The way in which pitch changes over the duration of a sound (e.g. initially rising)

Question 28

Describe a filter envelope.

Answer 28

May control filter cutoff or resonance.

Question 29

Describe a panning envelope.

Answer 29

How the spatialisation (e.g. left/right balance changes over time)

Question 30

What is one of the simplest envelopes?

Answer 30

A ramp. It starts at some arbitrary maximum amplitude and ramps to zero (e.g. fades outs).

Question 31

How are envelopes best described in synthesis?

Answer 31

By using breakpoint envelopes - Breakpoint envelopes consist of a series of points (time vs. value) which describe the shape of the envelope over time.
To be edited, they require a graphical UI.

Question 32

What is the most common form of breakpoint interpolation?

Answer 32

The most common form of interpolation is linear (straight lines), but other forms use curves and can have a significant effect:
Exponential, Logarithmic, Cubic, Sine