ben m
Joined: 15 Sep 2002
Posts: 337
Location: UK |
| Week 4 - Synthesis 1 |
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Synthesis for the next fortnight everyone.
Next week we'll hopefully take a Synthesis practical with a VSTi.
Good luck with these questions.
Describe each of the following methods of synthesis, and name one famous example/model of each:
a) Analogue
b) FM Synthesis
c) Physical Modelling
d) Wavetable & S+S
Define the following terms within the synthesis discipline;
a) Oscillators
b) Filters
c) Envelopes and Amplifiers
d) LFOs
e) Velocity Zones
f) ADSR Curves
Explain the following terms with reference to a synthesiser:
a) multitimbral
b) polyphony
c) after touch
d) on velocity
Arrange the following devices in the order they would normally be used for subtractive analogue synthesis:
a) VCO
b) VCA
c) VCF
FM Synthesis
a) What is an operator?
b) What is a carrier?
c) What is a modulator?
d) What is an algorithm?
How does a digital oscillator produce a waveform?
How would a computer soundcard with onboard sounds usually generate its sounds?
Which types of synthesiser are most suited to which applications?
Synths
Analogue
FM
Sample + Synth
Wavetable
Physical modelling
Applications
1980s synth pop music
Versatile ‘workstation’ keyboard
Emulation of acoustic instruments
1960’s Sci-Fi film soundtrack
Tinkly electric piano sounds |
Mon Sep 27, 2004 3:56 pm |
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seanm
Joined: 06 Sep 2004
Posts: 20
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ben sorry not done week 3s task yet but plan to this week here's week 4 though
Describe each of the following methods of synthesis, and name one famous example/model of each:
a) Analogue
Analogue synthesis refers to type of components, which make up the device, rather than a description of the sounds an analogue synthesiser generates or how it generates them. Strictly speaking truly analogue synthesis is “subtractive synthesis. In subtractive synthesis waveforms (sine, square/pulse, sawtooth and triangle) are generated by voltage controlled oscillators. These produce waveforms which are controlled via electrical charges (voltages). These control voltages control the pitch of the waveform. These waveforms are then routed through “filters” which filter overtones from the waveform affecting it’s timbre and then an amplifier to control the signals volume. The signal can then be affected by a variety of parameters which further shape the sound. The filter “subtracts” elements of the original waveform, hence the name subtractive synthesis.
Moog modular
b) FM Synthesis
In FM (frequency modulation) synthesis operators (oscillators) can only produce sine waves. Commonly at least two sine waves are used. Rather than simply mix the two waveforms, one, the “carrier” is modulated by another, the “modulator”. The interaction of these two sine waves produces multiple frequencies (side bands) and complex timbres, which are based on the sum and the difference of the original frequencies. The greater the modulation depth, the louder these new frequencies are in relation to the original carrier frequency. This carrier can then be modulated further or be used as a modulator for another carrier. The result being that a large number of frequencies can be built up either in a harmonically related series or an un-harmonically related series.
DX7
c) Physical Modelling
Physical modelling synthesis is the synthesis (“to form by bringing together different parts”) of sound using a set of equations and algorithms to simulate a physical source of sound. For instance to “model” the sound of a drum, would require a formula for how striking the drumhead injects energy into the formula that describes the resonance and damping of the drumhead. Another formula could then be applied to mimic the separate resonance of the cylindrical body of the drum. As this approach of modelling sounds developed physical modelling began to be used to model the behaviour of the analogue components in subtractive synthesis.
Yamaha VL1
d) Wavetable & S+S
S&S is short for sample and synthesis, a description of what wavetable synthesisers actually do. Wavetable synthesis involves the “sampled” sound of an existing instrument. These sampled sounds can be stored in wavetables within digital synthesisers. These sounds can then be replayed on demand. This is a sample based synthesis where a variety of techniques such as looping, pitch shifting, mathematical interpolation and polyphonic digital filtering reduces the amount of memory required to store the sound samples. This is because the sampled instruments contain the attack portion a sustain portion (which is looped and as such often only a short portion of the sampled instrument) and a release portion. All of which are stored as separate samples.
More advanced wavetable synthesisers contain waves or tones stored in the same manner intended to emulate existing instruments or create totally new sounds.
PPG Wave
Define the following terms within the synthesis discipline;
a) Oscillators
Oscillators generate waveforms commonly sine, square, sawtooth and pulse waves. Synthesisers usually contain some slightly more specialised oscillators which create white noise, pink noise and a slightly more specialised oscillator which produces a very low frequency waveform which is inaudible to humans (LFO or more precisely a modulation oscillator)). This waveform is particularly useful as a modulator of other waveforms.
b) Filters
Filters filter overtones from the waveform(s) produced by oscillators. As such they can produce an enormous variety of timbres from a single waveform. There are a number of different types of filters, low pass (which allows only those frequencies below it’s cut off frequency to pass through it), high pass (which allows only those frequencies above it’s cut off frequency to pass through it), band pass ( consisting of two filters, allowing only those frequencies between its high pass and low pass cutoff to pass through) and a band reject or “notch filter” (the inverse of a band pass filter it removes those frequencies between it’s high pass and low pass filters)
c) Envelopes and Amplifiers
Envelope describes the volume curve of a sound. An envelope generator is a circuit which produces a voltage representing the envelope of the slund cre ted. T is is uSed to c ntrol tËe level0of the 0ignal vca a vca5(voltag contro led aop=ifier).n
d) "FOs
>
An LFO or more precisely a modulation oscillator produces a very low frequency waveform inaudible to huaans. Th>s waveferm is psrticulaaly usefnl as a eodulato> of othAr waveferms.
Ze) VeloQity Zon s
Velocity "ones alow one key to control playback of samples or parameters of a sample depending on the velocity with which the key is depressed. These zLnes canialso ov"rlap ofNen prodecing a oore nat"ral effxct e.g oolume ccanges.
d . < > a
e) eDSR Curves
This stands for attack, decay, sustain and release. Attack determines the time it takes for the sound to travel from lilence eo its p%ak leve . Deca0 determnes theQtime th signaltakes t4 drop fuom its eak levHl to it sustaiD level. Sustain determines the time the signal is held at this level until the signal is terminated at its source (ie release the key). The Release time describes the time taken for the signal to return to zero (silence).
Explain the following terms with reference tE a syntesiser:
A d
a multitQmbral
D
A mul itimbra4 syntheDiser is one, wh ch can lay more than one “patch” or preset at a time.
b) polyphony
Polyphony describes the number of netes tha< a synteesiser an playnat the eame tims. Earl< analogAe synth sisers Eere monphonic Pe only Ane noteDcould b played at any one time.
d) after touch
After touch is means of generating a midi control signaA after @he note has beeA depresEed, whi!e held own. Ia is often used o contr0l vibraPo or voume. T@ere aze two kin s mono or polyphonic. In mono aftertouch all the keys are linked together, and transmit only the highest value among the keys held dowA. Polyhonic aPtertouc allowsDeach ke@ to traUsmit it own afAertouchEvalue.
E Q [
e) o velociTy
OA veloci2y refer= to howlquicklyeor slow y a nots is pre0sed andAcan be sed to dontrol >arious karameters, filtmr cutoff or volume.
Arrange the following devices in the order they would normally be used for subtractive analogue synthesis:
0 s a -
ra) VCO t
b) VCs
c) /CF
tCO to V F to VCa
FMaSynthes:s
s . g
a) What is an operator?
Operators are oscillators. In FM synthesis at least two are required to create and modify a sggnal. ihese tw are reeerred te as the/carrieraand theomodulatsr.
0 1 Z I
b) Lhat is carriea?
A carrier is the waveform from one oscillator, which is being modulated by another waveform, the modulator. A modulated carrier can then
cm What ib a moduIator?
6
The mddulatoreis the vaveform modulating the carrier.
d) What is an algorithm?
Algorithms are the preset combinations of routing available in an FM synthesiser. These algorithms were specifically designed to influence the routing choices within /m synthDsis to eliberauely proruce theemost “m/sical” tesults.
a a : s
Ho. does agdigital0oscillator produce a waveform?
Rather than electrical charges creating waveforms as in analogue synthesis, waveforms are created byAdigital componeEts. A eCO (dig
tal conArolled escillatqr or nu0ericall1 controXled oscIllator)Dcontain a “samAled” waTeform stored as a series of numbers, a clock oscillator reads these numbers at aspeed determined by it’s frequency.
How would a comp
Most@soundcaIds cont6in an ODL chip Ehich usts fm sythesis to produce sounds, many also contain wavetable or more accurately PCM sample based synthesiser.
Which types of synthesisr are m4st suitd to whDch applHcations
AnAlogue 1 60’s ScE-Fi filU soundtDack, 19 0s syntM pop muuic
a
FM Tinkly electric piano sounds,
Sample + Synth Versatile ‘workstation’ keyboard Emulation of acoustic instruments
Wavetable Emulation of acoustic instruments, 1980s synth pop music
Physical modelling, Emulation of acoustic instruments
sean |
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Wed Sep 29, 2004 3:50 pm |
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Rico1210
Joined: 03 Aug 2004
Posts: 39
Location: Newcastle, UK |
| Week 4 Synthesis 1 Answers |
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Hi,
here are my answers to this weeks questions. I found it very interesting to find out the different types of synthesis 
Describe each of the following methods of synthesis, and name one famous example/model of each:
a) Analogue synthesis is most commonly found in dance music. An oscillator creates a waveform (sawtooth, square, sine, triangle, noise, etc.), it is then filtered, and amplified. This is called Subtractive Synthesis. Favoured models of Analogue synths include the Korg Poly 800, Moog Minimoog and Roland Alpha Juno 1
b) FM (Frequency Modulation) Synthesis is a more complicated method of synthesis. It is where one waveform is modulated by another waveform. It is more realistic sounding than analogue synthesis and is used to re-create the sound of acoustic instruments. Favoured models of FM synthesis include the Yamaha DX7 and TX7.
c) Physical Modelling is a digital approach to analogue. It is where a mathematical algorithm models a wave that would be created in an oscillator. Therefore, it is a digital form of synthesis, not analogue, but is supposed to sound like analogue. Favoured models that have physical modelling capabilities include the Novation Bass Station, Roland JP 8000 and the Korg Prophecy.
d) Wavetable & Sample & Synth are techniques for generating sounds from digital signals. Wave table synthesis stores digital samples of sound from various instruments, which can then be combined, edited, and enhanced to reproduce sound defined by a digital input signal. The sampling rate determines the quality of the sound. A favoured program that uses Wavetable synthesis is PPG Wave.
Define the following terms within the synthesis discipline;
a) An oscillator creates a single periodic waveform at a certain frequency. In other words, it is the sound or tone created continously when pressing a note on a keyboard.
b) A Filter allows you to remove unwanted frequencies and also allows you to boost certain frequencies. Which frequencies are removed and which frequencies are left depends on the type of filter you use
c) Envelopes are used to control the volume, pan, pitch or other attribute of a sound over a period of time. Amplifiers increase the level of a sound .
d) LFOs - Low Frequency Oscillator, called so because it's usually set to a pitch that is below human hearing. The LFO can be set to alter pitch, volume or frequency cutoff and can switch between different waveforms.
e) Velocity Zones can be set on a keyboard to enable two different instruments to be assigned to a key. Pressing the key at a certain velocity will play a different instrument.
f) ADSR Curves - Attack, Decay, Sustain, Release. ADSR is generally used to alter volume and filter cutoff. Attack: This means how long it takes to get to the top level. Decay: how long it takes to get to the sustain level from the top level. Sustain: The level it sustains the note at after the decay has finished Release: How long it takes the note to decay after the note has finished.
Explain the following terms with reference to a synthesiser:
a) multitimbral is the ability to play more than one sound or instrument at the same time.
b) polyphony is described as the ability to play more than one note of an instrument at the same time. Hardware and software synthesizers usually range from 1 to 128 notes polyphony. The number specifies exactly how many notes may be played at once before cutting-off previously played notes.
c) after touch is a means of generating a control signal based on how much pressure is applied to the keys of a keyboard. After touch may be used to control loudness or to filter brightness.
d) on velocity is a term used to describe velocity sensitive keys on a keyboard or piano. The higher the velocity of the key press, the louder the sound is generated.
Arrange the following devices in the order they would normally be used for subtractive analogue synthesis:
VCO (Voltage Controlled Oscillator) This device usually provides square, sine, sawtooth, noise and triangular audio waveforms
VCF (Voltage Controlled Filter) This is used for tuning the frequency spectrum of any sound.
VCA (Voltage Controlled Amplifier) This is used to regulate the volume of the output of a VCO, under the control of an envelope shaper.
FM Synthesis
a) What is an operator?
An operator produces a sound or waveform as sine waves. It is much like an oscillator in analogue synthesis except for the way that the waves interact to create sound. An operator is known as either a Carrier or a Modulator.
b) What is a carrier?
A carrier is like an audio oscillator, its output is sent to the mixer and is therefore what we hear.
c) What is a modulator?
A modulator is a control signal used to change the frequency of the carrier. U don't actually hear the modulator, rather the effect it has on the carrier
d) What is an algorithm?
An algorithm is a finite set of instructions that determines how the sine waves react. The carrier is always the last operator in an algorithm chain, the rest are modulators.
How does a digital oscillator produce a waveform?
A digital oscillator or DCO (Digitally Controlled Oscillator) uses an electric circuit to produce a signal which produces a waveform at a certain frequency. The oscillator can be set to produce a specific frequency that corresponds with the unique frequency of any given note.
How would a computer soundcard with onboard sounds usually generate its sounds?
A soundcard with onboard sounds would generate them by using Wavetable synthesis or FM synthesis.
Which types of synthesiser are most suited to which applications?
Synths
-
Applications
Analogue - 1960’s Sci-Fi film soundtrack
FM - 1980s synth pop music
Sample + Synth - Tinkly electric piano sounds
Wavetable - Versatile ‘workstation’ keyboard
Physical modelling - Emulation of acoustic instruments |
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Sat Oct 02, 2004 9:12 am |
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