modulation synthesis

Question 1

What is additive synthesis?

Answer 1

• Adding / Mixing / Summing Oscillators

- Most commonly to sum basic waveforms
(e.g. sine waves) to produce complex sounds

Question 2

What did Thadeus Cahill’s Telharmonium use?

Answer 2

Thadeus Cahill’s Telharmonium used additive synthesis to produce different timbres.

Question 3

What can additive synthesis require?

Answer 3

A lot of oscillators for complex tones. Early digital synthesising computers were non-realtime, instead taking time to generate a digital audio file.

Question 4

What can produce more complex wave forms?

Answer 4

Varying the weight of harmonics.

Question 5

Does additive synthesis only use harmonics?

Answer 5

No. Additive synthesis need not only use harmonic frequencies (frequencies which are an integer multiple of some fundamental frequency)
For example, bell sounds are composed of frequencies that are inharmonic
i.e. not in an integer relationship

Question 6

What is the general term used to describe the simple components in additive synthesis?

Answer 6

Partials (may be harmonic or inharmonic)

Question 7

What do inharmonic waves include?

Answer 7

Inharmonic waves include partials that are not “harmonic” (and should only be called “partials”)

Question 8

What does the balance of harmonic and inharmonic partials determine?

Answer 8

How consonant (or dissonant) a sound is.

Question 9

What is the real power of additive synthesis?

Answer 9

Each partial or harmonic can be controlled independently

e. g. through the use of multiple amplitude envelopes
- Early electronic composers (e.g. Stockhausen) experimented with this detailed level of control.

Question 10

What are Walsh functions?

Answer 10

Walsh functions use rectangular waveforms (complex pulse/square-like waves) which may be summed to produce other waveforms
- It’s even possible to create sines from rectangles.

Question 11

What will many synthesisers allow you to sum?

Answer 11

Many synthesisers allow you to sum multiple oscillators, generating various wave types.
Used to create richer tones with fewer oscillators
e.g. ES P, ES 1, Novation KS Rack

Question 12

What do modulation frequencies above 20kHz introduce?

Answer 12

Audible modulation artifacts: sidebands

Question 13

What is the main benefit of modulation synthesis techniques?

Answer 13

Complex and time varying sounds can be made with only a few oscillators (which would need hundreds of oscillators using additive synthesis)

Question 14

What is ring modulation?

Answer 14

Ring modulation is simply the multiplication of two audio signals (usually at least one is a sine wave)
Amplitude x Amplitude

Question 15

What are the two signals involved in ring modulation?

Answer 15

The two signals involved are:
C (carrier) x M (modulator)
- If both C and M are sine waves then the result of will be a mix of frequencies Cf+Mf and Cf–Mf

Question 16

Give an example of ring modulation.

Answer 16

E.g. if a 700Hz sine and a 300Hz sine are RM’d the result will be the same as mixing 400Hz and 1000Hz sine waves (though amplitude is slightly affected)

Question 17

What are sidebands?

Answer 17

The frequencies generated by the RM

Question 18

What happens if the frequencies of C and M are in an integer ratio?

Answer 18

Harmonic sound will be produced (otherwise they are inharmonic: bell-like)

Question 19

Why do complex carriers (e.g. natural sounds) become very complex using RM?

Answer 19

There will be a pair of these sidebands for every frequency component in the carrier signal

Question 20

What are the components in Chowning FM?

Answer 20

A sine wave modulator which modulates the frequency of a sine wave carrier.

Question 21

How is FM similar and different to RM?

Answer 21

Like RM, FM generates sidebands but FM can easily generate many more with only two simple oscillators…

Question 22

What do the amplitudes of the sidebands vary depending on?

Answer 22

The amplitude of the modulator. Generally, the higher the amplitude of the modulator the louder the sidebands (making the sound brighter)

Question 23

What did Yamaha name the components in its FM synths?

Answer 23

‘Operators’, the operators may be connected in various ways to modulate each other or themselves (i.e. feedback)

Question 24

Describe a multiple carrier.

Answer 24

• (single modulator)

- Useful for simulating vocal sounds

Question 25

Describe a multiple modulator.

Answer 25

• (single carrier)

- Has been used to generate piano-like tones