ben m
Joined: 15 Sep 2002
Posts: 337
Location: UK |
| Week 4 - Synthesizers 1 |
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Hi everyone,
sorry for the late post but some strange ISP problems this morning.
Ok, I want good in-depth answers for these, ensuring you fully understand the fundamentals of synthesis.
Lets go;
 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
_________________
ben@audiocourses.com |
Mon Sep 22, 2003 8:27 pm |
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mrg4u
Joined: 08 Sep 2003
Posts: 7
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| synthesisers pt 1 - |
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Here is this weeks work....
regards G
 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
a) Analogue Synthesis - Analogue Synthesis is making sounds from electronic waveforms as opposed to digital or sample based synthesis. Many still love to use analogue as opposed to digital as many claim, digital synthesis sounds unnatural. However these days the replications of famous synth via digital is virtually, and sometimes impossible to tell the difference. Many synths however are still favoured by the analogue enthusisast these include the tr808-tr909 classic synths which have stood the test of time and can now go for a small fortune.
b) FM Synthesis -FM synthesis is quite efficient in that it can create complex sounds from a few simple sine waves. Frequency modulation is, the output signal of one oscillator modulates the frequency of another oscillator. Since 1985, the Yamaha DX Synthesisers has become a very popular form of sound generation. The effect of frequency modulation can generate interesting sounds to spooky and eerie sounds.
Physical Modelling - Physical modelling is different from the other types of synthesis, its when you create and control what makes that sound. as opposed to creating the sound directly. By manipulation of processes which describe acoustic behaviour, its possible to replicate any sound source. eg. the replication of a violin bow is done via physical modelling. Yamaha's VL1 and VL1m are all examples of modelling synths.
Wavetable S + S - Wavetable synthesis is based on recordings of actual sounds and instruments to produce sound. It lets u create a digital sample and change it altering the pitch. Its a very good method of producing much more accurate sounds. Waldorf is an example of a wavetable synth.
Define the following terms within the synthesis discipline;
a) Oscillators
b) Filters
c) Envelopes and Amplifiers
d) LFOs
e) Velocity Zones
f) ADSR Curves
a) Oscillators- In synthesis oscillators provide the power waveforms which is what ultimately controls the sounds shape and characteristics.
b) Filters - Filters are devices which allows the user to remove certain components of a sound depending on its frequency. From single waveforms filters can produce thousands of different timbres. In order for the filters to remove these components of sound their are many types of filters each one specialises at a certain role.
Filters have two specific sound sculpting tools also, these being cut off and resonance.
Cut off- Cut off is basically the threshold, meaning ( the frequency at which the filter begins to change the sound. Dependant on what filter is used, baring in mind the different frequencies is what determines the cut off frequency.
Resonance- This is what spices up a filters sound, by means of boosting the frequency band which surrounds the cut off frequency of a given filter. Its an essential parameter for any filter although it doesnt sound much it changes the sound shape in a dramatic fashion. E.g. resonance is what is responsible for the classic wah sound.
Low pass- This is the most popular (LPF) filter which allows only the frequencies through that lie below its cut off frequency. Put simply a LPF allows the low frequencies to pass and removes only the high frequencies.
High pass - A filter which allows only the high frequencies to pass which are above the cut off frequency. Usually used to shape thin tinny sounds etc.
Band pass - A Band Pass Filter contains a Low Pass Filter, and a High Pass Filter, so this allows selected frequencies to pass while killing all other frequencies above and below the cut off point.
Notch filter - This filter has a very narrow bandwidth and is usually used to filter out a narrow band of frequencies.
c) Envelopes and Amplifiers - An Envelope is used for changing the shape of a sound, in some fashion over a period of time. eg A sound starts off loud (attack) then gradually decreases in volume ( decaying). This is all controlled by the envelopes individual shape.
Envelopes are very good at replicating how sounds change over time, eg, A Bell struck with a hammer will instantly be loud then over the period of time will slowly die away. That particular example would be controlled via the amplifier envelope. Another envelope is. The Filter envelope controls the filters sound over a given period of time, its a very powerful envelope as it controls the overall timbre of a sound. A Filter envelope is what makes the essence of a sound.
Amplifiers - This is what determines the overall volume of the signal routed from the oscillator via the filter.
LFOS - Low Frequency Oscillators is a wave that repeats at a slow rate. Their are many different shaped Lfos and each one determines the frequency of a waveform. If we were modulating pitch, the waveforms would change it in the following ways.
The most common Lfo, waveforms are.......
Sine - The Sine wave is a smooth waveform and the pitch would also be smooth.
Sawtooth - This Lfo is fantastic for creating repetitive backwards effects. This wave slowly decreases then suddenly changes back up. The sounds pitch would follow the same pattern.
Square - The square waveform changes suddenly and the pitch will sudddenly change from one pitch to another.
Triangle - The Triangle waveform produces a soft modulation curve it contains all overtones although these are severly dampened. Its sound is closer to a sine than a sawtooth wave.
Velocity Zones
Velocity controls the playing parameters of sounds. for e.g. the information relating to how hard you press down on a key when u initially strike it this is velocity. The velocity zones are the parameters to which individual sound have been set to. By using velocity zones u can recreate the response of the actual instrument. So if the velocity levels were set to quite high the response of the instrument would be much louder than velocity settings which are lower.
ADSR Curves
ADSR Curves control the Attack. Decay , Sustain , and Release of a given sound. Useful for giving a sound varifying character from the momement the sound is pressed to the momement its released. In relation to synths when the key is pressed the envelope is triggered. This means it starts to raise from zero to maximum level. How long this takes depends on the attack setting. If the attack time is set to 0 the envelope reaches full level instantly. If you routed the envelope to control the filter raising the attack will give the sound a wah sound. Once the envelope has reached full level it starts to fall back again this is determined by what the decay time is set to. The level of the envelope after the decay is determined by the sustain setting. E.g. creating a flute sound would have a fairly high sustain setting, when the envelope is being used to control volume, since a flute tone basically stays at a steady level for as long as it is played. Another example would be replicating a piano, the sustain setting would be set to 0, since a piano sound decays to silence when the key is held long enough. The envelope stays at the sustain level until the key is released. The time it takes for this to happen is set by the release parameter. This works in the same way as the decay, only it does not take affect until the fingers are no longer applying pressure.
Explain the following terms with reference to a synthesiser:
a) multitimbral
b) polyphony
c) after touch
d) on velocity
Multitimbral
Multitimbral is when the synth can play more than one sound at a time.
Polyphony
Polyphony is the number of notes that the synth can play simultaneously. This is usually set to the number of channels the unit has. For example, on a 16 channel unit with 64 note polyphony, the synth can play 64 notes at a time, spread out over 16 different instruments.
Aftertouch
This is when synthesisers respond to the pressure applied to the keys. The key pressure normally controls the volume of the note, and can sometimes affect the filtering as well. Channel aftertouch is a when all the notes on a midi channel have the same volume.
Arrange the following devices in the order they would normally be used for subtractive analogue synthesis:
a) VCO
b) VCA
c) VCF
These are the three main components used in a analogue synthesiser
VCO - VCF - VCA = Voltage Controlled Oscillator (VCO) ---> (VCF) --->Voltage controlled Filter ---> (VCA) Voltage Controlled Amplifier. (VCA)
The VCO produces the basic waveform, its then fed to the VCF which changes or decides the timbre and harmonic content of the sound, and finally the VCA controls the volume via the envelope generator, (ADSR) which decides how the sound is shaped over a period of time how quickly it sounds, how long it stays and how slow or quick its released.
FM Synthesis
a) What is an operator? - The oscillator is often called the carrier.
b) What is a carrier? The carrier is one of the two sinewaves
c) What is a modulator? This is the other sinewave and the modulating wave changes the frequency of the carrier wave.
d) What is an algorithm? The algorithm determines how each operator interacts with another; which operator is fed into another, or added to another.
How does a digital oscillator produce a waveform?
Information source - www.tweakheadz.com
The two types of oscillators. Voltage Controlled Oscillator (VCO) or Digitally Controlled Oscillators (DC0). . Digital Oscillators produce a waveform at a certain frequency. A digital component rather than a voltage generator controls the oscillators. However in a DCO the actual waveforms are generated in the usual analog way. The oscillators frequency can be manipulated by modulation of another oscillating signal to determine a different pitch or frequency. It can also produce a sine wave or even tone of that frequency. Also when asked it can produce a specific waveform such as saw sine tooth triangle etc.
How would a computer soundcard with onboard sounds usually generate its sounds?
The soundcard generates sound from digital data, using either a digital to analogue converter or a FM synthesis chip. It can also record and control midi instruments. In order for your computer to generate sounds the soundcard is needed. Also soundcards carry electronics to generate midi data. The two types of midi generation are. Wavetable synthesis. The generation of digitised samples to produce a more realistic sound, and FM Synthesis. The simulation of musical notes by modulating the frequenccy of the base carrier wave.
Which types of synthesiser are most suited to which applications?
Synths - 1980s synth pop music
Analogue - Tinkly electric piano sounds
FM - 1960’s Sci-Fi film soundtrack
Sample - Synth - Versatile ‘workstation’ keyboard
Wavetable - Applications
Physical modelling - Emulation of acoustic instruments
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Wed Sep 24, 2003 9:41 pm |
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mommi
Joined: 21 Apr 2003
Posts: 47
Location: Tallinn, Estonia |
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Hi all,
This is what I could get done. Huge amount of questions in Recording Techniques took so much time away that I started to use copy & paste here. Not good. 
Comments are very welcome, since I'm new to synthesis.
Describe each of the following methods of synthesis, and name one famous example/model of each:
a) Analogue
Useful link:
http://tyala.freeyellow.com/2ansynth.htm
In analogue synthesis, the sound generators (oscillators), as well as filters and envelope contours are controlled by voltage. So there are VCOs (Voltage Controlled Oscillator, means the oscillation frequency is dependent on the driving voltage), VCFs (Voltage Controlled Filter, having the cutoff fequency and resonance dependent of voltage applied) and VCAs (Voltage Controlled Amplifier, an amplifier with amplification factor changing along with driving voltage).
Since that technology applies filtering to initially more complex (bright) sound produced by an oscillator, it is called subractive synthesis.
Example: Sequential Prophet T8
b) FM Synthesis
http://tyala.freeyellow.com/2fmsynth.htm
http://www.sfu.ca/sca/Manuals/247/midi/Wavetable.html
In FM (Frequency Modulation) synthesis there are two ((at least, in reality four or six) oscillators used to produce a sound. The frequency of one oscillator - called the carrier - is modulated by output from another oscillator - modulator. In this case the oscillators produce pure sine waves, as opposed to overtone-rich signals in subtractive synthesis. If the modulating signal is in the audible range, then the result will be a significant change in the timbre of the carrier signal.
FM synthesis became popular with Yamaha DX7 range of synths. Roland JX-8P is another example.
c) Physical Modelling
Two quotes here, as I feel they carry good explanations.
From
http://www.harmony-central.com/Synth/Articles/Physical_Modeling/
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In the history of sound synthesis, there have been two different general methods for synthesis of musical instrument sounds. One approach is to look at the spectrum of a real instrument and try to recreate it. This includes methods such as additive synthesis and frequency modulation (FM). These produce sounds with similar structure, but the parameters involved have no relation to the physical parameters of an instrument. The other popular approach is to use a sample of the instrument, such as in wavetable synthesis and samplers. In both of these cases, you're creating sounds without any consideration for how the real instrument actually creates those sounds.
With physical modeling on the other hand, you are not creating the sound directly - you are creating and controlling a process that produces that sound. You define the process which models the actual instrument, and then when you play this synthetic instrument, you are specifying some of the necessary parameters needed to make the sounds.
From
http://jpmullan.com/stan/
Synth Glossary:
Physical modelling is a method of synthesis in which a mathematical model of the instrument being synthesized is used to create the sound. It is the best way of approximating a real instrument.
Examples: Yamaha VL1, Korg Prophecy
Another helpful link:
http://www.enlightenedsystems.com/vl/physmodl.htm
d) Wavetable & S+S
http://www.harmony-central.com/Synth/Articles/Wavetable_101/Wavetable-101.pdf
Wavetable synthesis uses a waveform lookup table that contains digitised samples of a period of complex waveform. The lookup table can be filled with sounds of real instruments, which makes that form of synthesis sound more natural.
Example: Roland RS-50
Define the following terms within the synthesis discipline;
a) Oscillators
Oscillatiors are signal generators. The signals are either those that will eventually, after filtering and envelope-shaping find their way into the final sound, or those used for driving/modulating other devices.
b) Filters
Filters shape the output from oscillators in timbral terms. They are capable of blocking frequency components above or below some specified frequency (low-pass and high-pass filters, respectively), or amplifying/damping some frequency band (band-pass filters).
c) Envelopes and Amplifiers
Envelopes are what determine the changes in waveform over time, transients. Sounds from natural instruments always have changing parameters, the simplest being their level sounds have an onset time, for example, the time it takes to reach some more permanent level. Envelope devices have four different parameters to operate with: attack, decay, sustain and release, described below. These can be used to control either the signal's amplitude behaviour through voltage controlled amplifiers, or timbral characteristics through voltage controlled filters.
Amplifier is a device to adjust the sound's level, or loudness.
d) LFOs
LFO, short for Low Frequency Oscillatior, is a device to generate low frequency signals. Output from LFO can be used to drive other devices like VCOs (to get periodic changes in their frequency) or VCAs (for periodically changing amplitude). There are several types of waveforms produced by LFOs, like sine wave, sawtooth, triangular or square.
e) Velocity Zones
Velocity expresses how fast (hard) the key has been pressed, an equivalent to how loud the player wants the sound to be. Since most instruments change their timbral characteristics according to how loud they are played, the more realistic synthesis has take into account that fact. To do this, the velocity is quantized into zones and different waveforms (samples) associated with them. The more zones there are, the more realistic it can be.
f) ADSR Curves
From
http://jpmullan.com/stan/
Synth Glossary:
ADSR is a type of envelope generator. It has four stages - the attack of the note where it build up to its initial volume peak when you press the key, the decay where it goes back down in volume to the sustain level where it stays until the player releases the key and it fades out.
Explain the following terms with reference to a synthesiser:
a) multitimbral
Multitimbral synthesizer is the one capable of producing several different timbres at once, in contrast to being able to generate only one instrument sound at a time. The number of different instruments that can be used together is expressed by timbrality. Different sounds are nowadays represented by program or patch numbers in synths, the table of patch numbers and corresponding sounds called patch map.
b) polyphony
Polyphony describes how many notes can be played on the synthesizer at any given time. Modern synths are capable of producing up to 64 notes at a time. The term polyphony is used because first synthesizers (analogue) did not allow playing more than one note at a time they were monophonic.
c) after touch
From http://jpmullan.com/stan/ Synth Glossary:
Aftertouch is a means of generating a control signal based on how much pressure is applied to the keys of a MIDI keyboard. Most instruments that support this do not have independent pressure sensing for all keys, but rather detect the overall pressure by means of a sensing strip running beneath the keys. Aftertouch may be used to control such functions as vibrato depth, filter brightness, loudness and so on.
d) on velocity
Note-on velocity tracks how fast (hard) the key was hit. This is usually associated with dynamics.
Arrange the following devices in the order they would normally be used for subtractive analogue synthesis:
a) VCO
b) VCA
c) VCF
VCO --> VCF --> VCA
FM Synthesis
a) What is an operator?
The two oscillators participating in FM synthesis are called operators.
b) What is a carrier?
Carrier is an oscillator (operator) in FM synthesis that is being modulated by another oscillator (operator). The latter is called a modulator.
c) What is a modulator?
Modulator is an oscillator (operator) in FM synthesis that is modulating the other oscillator (operator). The latter is called a carrier.
d) What is an algorithm?
From
http://tyala.freeyellow.com/2fmsynth.htm
:
Algorithms are the preset combinations of routing between operators available to you. The carriers are always the last operators in any algorithm chain and all other operators are modulators.
How does a digital oscillator produce a waveform?
From Wavetable-101.pdf mentioned above:
The waveform generator uses a circular table of sequential waveform values. Driving pulses of desired fundamental frequency are sent to a phase accumulator for address generation, that address is then used to read the corresponding digital sample value from the table. The intermediary step is interpolation between adjacent wavetable samples because the address generated by the phase accumulator will not generally fall exactly on a wavetable sample.
How would a computer soundcard with onboard sounds usually generate its sounds?
The most common types of onboard synthesis on computer soundcards are FM and wavetable synthesis.
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
1960s Sci-Fi film soundtrack
Tinkly electric piano sounds
Just guessing:
Analogue - 1960s Sci-Fi film soundtrack (because analogue is the oldest)
FM - Tinkly electric piano sounds
Sample + Synth - Versatile workstation keyboard
Wavetable - 1980s synth pop music (http://www.hermannseib.com/english/synths/ppg/history.htm confirmed that guess)
Physical modelling - Emulation of acoustic instruments (sure) [/b]
So much then.
It is 4:00 a.m. now, I'm still looking at the screen! So I'm afraid I will very intentionally skip the practical, just to stay alive.
See you on Sunday,
tarmo |
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Sat Sep 27, 2003 9:05 am |
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Albow
Joined: 02 Sep 2003
Posts: 27
Location: Spain |
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Along with mrg's earlier postings, these links were of some help:
http://whatis.techtarget.com/definition/0,,sid9_gci497888,00.html
http://www.bsu.edu/web/kkothman/mumet327/week2-2/sld001.htm
http://aulos.calarts.edu/pipermail/music-dsp/2002-April/015502.html
Describe each of the following methods of synthesis, and name one famous
example/model of each: a) Analogue
Analogue synthesisers work by manipulating sounds with non-digital frequencies.
This could be elctronic circuits providing voltages or radio frequencies for
example The earliest anaalogue syntesiser was the Theremin which used radio
frequency oscillators. Radio frequencies were tuned to each other to produce a
whining sound. The note could be manipulted by moving hands around a pole on
the right and the volume altered by moving the left hand around a loop aerial.
b) FM Synthesis
By this method, a musical sound is produced by using one waveform to modulate
the frequency of another waveform. The frequency on the original causes
another to mic it. Sounds are simulated by using algorithms to create sine
waves that are as close to the sound as possible.
For example, the sound of a guitar can be simulated, although the result does
not really sound very much like a guitar
c) Physical Modelling
Physical Modelling is the method of devising a synthesiser that is based on the
physical attributes of the instrument that the synthesiser's sounds are
modelled upon. FM synthesis does not do this - it attempts to mimic sounds by
approximating them through its own sound-producing circuitry, while having no
knowledge of the instruments' physical form and how it is used to produce
sound.
d) Wavetable & S+S
Wavetable has evolved from FM to produce more accurate sounds of the
instruments it imitates by using samples. The sound of a real instrument is
digitally reproduced and stored on a lookup table in the synthesisers Read Only
Memory. It is then reproduced when the signal is received from the instrument
or program requesting the sound.
Define the following terms within the synthesis discipline;
a) Oscillators
This would be any device that is used to generate electric oscillations or
waves. This could be the synthesiser keyboard itself which will provide the
voltage for the electric oscillations used to produced sound frequencies
b) Filters
A filter is a device that frequencies pass through and governs which are not
allowed to pass through and which ones are passed through to help generate the
sound. This may be cutting off undesirable overtones to a sound to make it
smoother and purer.
c) Envelopes and Amplifiers
The envelope of the sound is the typical pattern that that sound makes over a
particular period of time. For example one ring of a bell will follow a
certain pattern od harmonics and volume before and will cease at a certain
point. This is its envelope. A synthesised sound will be given an envelope to
replicate the given sound as accurately as possible.
Amplifiers are used to add volume to a sound created by the oscillator. The
envelope will dictate how the amplifier is used to create the sound and when.
d) LFOs
Low Frequency Oscillators produce the chorus effect together with a short delay
on the signal. The delay provides the doubling effect and the LFO provides
moves the pitch slightly up and down, adding a quiver to the effect.
e) Velocity Zones
These zones control how loudly a note will sound once it is pressed.
f) ADSR Curves
ADSR stands for Attack Decay Sustain Release. The curves are the waveforms
that the sound takes with regard to these characteristics.
The attack is the amount of time it takes for a note to reach its maximum
volume. How long it stays at its maximum level before it falls slightly in
volume to ring out is the decay of the note. The sustain is how long the note
can then stay at that level after the decay. The release is the time that the
note takes to return to zero.
Explain the following terms with reference to a synthesiser:
a)multitimbral
Multitimbral concerns the amount of sounds a synthesiser can produce
simultaneously. If a synthesiser is 32-part multitimbral it can play 32
different sounds at the same time
b) polyphony
Polyphony is the ability to play several notes at a time. The first synths
were monophonic and could only play one note at a time. So the synth would
play out one line in a song. However with polyphony, several notes and chords
can be played firstly together, or introduced on top of another, without
subtracting from the first chords' sound.
c) after touch
The after touch is the effect that pressing the key hard or soft will have on
the noise produced by the synthesiser, and governs how sensitive the keys are
compared to an acoustic piano.
d) on velocity
Arrange the following devices in the order they would normally be used for
subtractive analogue synthesis:
a) VCO
This comes first. It is the Voltage Controlled Oscillator which is tha basic
waveform fed into the synthesiser.
c) VCF
The Voltage Controlled Filter then decides which waveforms are left out and
which are filtered through to make the desired sound due to the information
recieved from the keys.
b) VCA
The Voltage Controlled Amplifier then controls the amount of amplification
required thoughout the sound envelope to imitate the sound needed as accurately
as possible
FM Synthesis a) What is an operator?
An operator in FM is the original oscillator from which the sound is produced
b) What is a carrier?
The operator modulates the frequency of another sine wave which is the carrier
c) What is a modulator?
The modulators accompany the operator and carrier and alter the sound so that
the sound becomes the one indicated to the program
d) What is an algorithm?
The algorithm is a preset mathematical equation that if chosen will put into
place a combination of carriers and operators and modulators to produce the
particular sound desired.
How does a digital oscillator produce a waveform?
An algorithm for the perfect sine tone exists in a table and the table is
accessed each time a note is requested. The waveform itself is the same as an
analogue oscillator's but is controlled by a digital clock.
How would a computer soundcard with onboard sounds usually generate its sounds?
You would not expect the onboard card to have as many features as a PCI plug-in
card soundcard. It would most likely use FM synthesis and a wavetable with
sound samples. An add-on soundcard will have a database of analogue samples
which are referenced and reproduced by digital commands. The card will have
enough processing power to reproduce sounds faithfully in combination and in
real time.
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
Is this a mix and match exercise?
If so....
Synths 1960?s Sci-Fi film soundtrack
Analogue Tinkly electric piano sounds
FM 1980s synth pop music
Sample + Synth Versatile 'workstation' keyboard
Wavetable Applications
Physical modelling Physical modelling |
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Sat Sep 27, 2003 9:28 pm |
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julesf
Joined: 31 Aug 2003
Posts: 58
Location: Southampton, UK |
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That took me back to the good old days when Synths were Cool 
<b>Describe each of the following methods of synthesis, and name one famous example/model of each:</b>
<b>a) Analogue
b) FM Synthesis
c) Physical Modelling
d) Wavetable & S+S </b>
Robert Moog developed analogue synthesis in the late 60's early 70's
it is a system that uses Oscillators to produce sound waveforms and filters and envelope shapers to alter the waveforms. As this process actually takes harmonics away from the waveform to shape the sound it is know as subtractive synthesis. The various components can be varied in real-time by altering the amplitude of a control voltage that is applied to them. The control voltage is between 0 and 5 volts and when this is applied to the filter and allowed to vary it produces a filter sweep. The sound of a true analogue Ladder network filter is unique and cannot be reproduced by digital filters and is known for the classic MOOG scream sound. The envelope generators and voltage controlled amplifiers control the attack, decay, sustain, and release of the sound. On a good analogue synth the control voltage patching should be very extensive and sometimes only a patch board will do for this. In the early days each component was an individual unit, all units were then connected (patched) together by cables, these are the early modular synths that we here of today. Some can take up a whole room. The synth has to be set up by the use of patch cables and the setting of potentiometers therefore there is normally no storage for sounds though this was addressed in later models and the new Voyager. Another disadvantage is that most models were monophonic and could only play one note at a time although this was also addressed in the late 70's early 80's with the introduction of the polymoog, though this could only play 6 notes at a time. Early models also suffered with tuning drift due to temperature change. The sound of a good old analogue synth is completely unique; it has a fat sound and is great for basses as well as leads. For this reason even all these years later they are still very popular and vintage machines are changing hands for large sums of money.
My personal favourite is the MOOG ROUGE, although there are bigger more impressive Moogs this one was small and portable, tuning drift had been addressed
And it came complete with that fat MOOG sound right out of the box. Wish I still had it! lol
FM (Frequency Modulation) synthesis was introduced in the late 70's early 80's and was seen on Yamaha keyboards the most famous being the DX7 The system uses operators as the sound source rather than oscillators. Unlike analogue, which is a subtractive synthesis, FM is an additive synthesis. It uses a carrier frequency, which is modified, or modulated by the modulator operators thus changing the waveform by the addition of the characteristics to the carrier. There are normally many operators in a FM synth the last in the chain is the carrier and the other operators act as the modulators. Algorithms define the control of the synthesis.
Generally these days the sounds are not very interesting and the synths are a nightmare to program! In fact many users just used the pre sets as it was considered at the time rocket science to program your own patches. Patches could be stored but there was usually only about 32-user address's these could usually be backed up to cassette tape or flash memory. I had a DX11 (and yes I did program it) which was a pretty good FM synth if you like that sort of thing, I didn't.
For those who are interested:
http://www.xgfactory.com/downloads/FMINFO.pdf
Physical modelling. This process uses computer modelling to generate simulations of various instruments. The basics of the physical modelling system are the reactor and the exciter. The reactor is a fairly static model of the type of instrument to be emulated; however the reactor is variable and is intended to alter the tonal characteristics of the model. For the sound of a flute you would choose a wind instrument exciter model and then modify the reactor to provide the required emulation. In some emulation's coupled resonators are used to allow for feedback within the instrument i.e. when a clarinet is blown the reed vibrates and produces the sound, the sound causes the wooden instrument to resonate and this in turn causes further harmonics to be introduced back into the reed. Coupled resonators allow for this, and include it as part of the modelling. Digital wave-guides and granular synthesis can also be used to modify the sound further. The KORG Z1 is a classic physical modelling synth.
<b>Check this excellent link for the very talented Richard James.</b>
http://www.headjog.co.uk/report/#pm
<b>Be sure to check his virtual CV, this is the most sensible use of Flash I have seen so far!
</b>
http://www.headjog.co.uk/cv/
Wavetable uses a table of digital algorithms to create the base waveforms. These are then mixed and modified to create the final sounds. The main advantage of wavetable synthesis is that it is cheap and compact and uses less processing time than other systems, though it is not good enough generally as the core synthesis in professional synthesisers. PCM synths use Pulse coded modulation to play back what is basically a digital recording of the sound source. This produces a faithful reproduction of many instruments and makes for a great workstation engine. Some consider that a PCM synth does not offer enough flexibility to the user. Various manufactures have addressed this by either including a form of synthesiser which is normally a physical modelling synth or offer such a synth board as an optional extra. My personal favourite is the KORG TRITON RACK. With additional MOSS board which is based on the KORG Z1 physical modelling engine. An example of a wave table synth can be found in the Creative Labs Sound Blaster PCI Card.
<b>Define the following terms within the synthesis discipline;
a) Oscillators
b) Filters
c) Envelopes and Amplifiers
d) LFOs
e) Velocity Zones
f) ADSR Curves</b>
Oscillators produce the initial waveform that we hear form the synth.
Filters remove (subtractive) harmonics to modify the waveforms produced by the oscillators.
Envelopes and amplifiers control the amplitude and timbre of the sound perhaps to emulate real instruments. They do this by altering the amplitude in real time and providing envelope feedback to the filters.
Low frequency oscillators act as modulators and can be used for expression i.e. vibrato or to control filter sweeps or any other modulation control.
Velocity Zones can be set on the keyboard of usually a PCM synth and used to control aspects of the sound when a velocity threshold is exceeded. An example of this is that a piano may be set up with the 3Rd octave set as a velocity zone. When the velocity of 85 is exceeded in this zone only a string patch is also triggered underneath the piano patch. This is also known as velocity gating.
ADSR Curves. Attack Decay Sustain Release. Describes the amplitude curve of an ADSR envelope generator. Each parameter can be set Attack allows for the sound to gradually rise up in level until it reaches max level. However the attack can be set so the sound is staccato like a drum hit. Then there is a delay before the sound drops down to the sustain level. Sustain now defines how long the sound sustains for, before dropping off and dying away which is controlled the release.
<b>Explain the following terms with reference to a synthesiser:
a) multitimbral
b) polyphony
c) after touch
d) on velocity</b>
multitimbral: key board or sound module has 16 timbres (sound producing shaping generators) one timbre is assigned to each midi channel 1 - 16 all 16 can play midi events from a midi sequencers at once. i.e. T1 Bass T2 pad T3 Synth and so on.
The system is used by General MIDI and other standards but may use with no special format.
Polyphony. Ability for a sound generator to play more than one note at a time, this could be from say just 6 notes max to 128 notes depending on the synth. If a keyboard is not polyphonic then it is monophonic and will only play one note at time.
After Touch allows further information to be used normally modulation but often can be assigned aftertouch is activated by pressing the key or key's on the keyboard a little harder. Not all keyboards support aftertouch so if your keyboard does not but your sound module does you may be able to send the after touch events by another device such as a joystick or directly from the sequencer.
On Velocity is a system that emulates the weight that a key was pressed. It comes from the pianoforte, which as the name suggests can be played loud or soft depending on how hard the keys is played. Velocity emulates this by assigning a MIDI velocity value of between 0 & 127. Though it does not actually check the weight of the key stroke but measures the speed the key moved it never the less does seem to work quite well. Mostly the sound generator will not just interpret the volume from the MIDI event but also the Timbre or brightness of the sound. This again makes the system more realistic.
<b>Arrange the following devices in the order they would normally be used for subtractive analogue synthesis:</b>
a) VCO
b) VCA
c) VCF
VCO > VCF > VCA
<b>FM Synthesis
a) What is an operator?
b) What is a carrier?
c) What is a modulator?
d) What is an algorithm?</b>
The operator either produces the sound source or shapes the sound source depending whether it is set as a carrier or modulator.
The carrier is an operator set to produce the sound source.
The modulator is an operator set to modulate the carrier and shape the sound source
The algorithm is a series of instructions used to full fill a process or task. In this case a pre-set algorithm to shape the sound in some way.
<b>How does a digital oscillator produce a waveform? </b>
By using an algorithm which presents digital data to the DAC a perfect sine wave can be produced or other waveforms.
<b> How would a computer soundcard with onboard sounds usually generate its sounds?</b>
Either by FM synthesis (old cheaper cards) or Wavetable synthesis. High quality cards may use PCM synths.
<b>Which types of synthesiser are most suited to which applications? </b>
<b>Synths
Analogue
FM
Sample + Synth
Wavetable
Physical modelling</b>
<b>Applications
1980s synth pop music
Versatile ‘workstation’ keyboard
Emulation of acoustic instruments
1960’s Sci-Fi film soundtrack
Tinkly electric piano sounds</b>
<b>1980's pop:Fm synth,</b> Analogue synth
<b>Versatile workstation keyboard:</b>Sample and Synth
<b>Emulation of acoustic instruments:</b> Physical modelling synth
<b>1960's Sci- Fi Film soundtrack:</b> Analogue synth
<b>Tinkly electric piano sounds:</b> FM synth, Wavetable synth
Cheers,
Jules  |
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Sat Sep 27, 2003 10:32 pm |
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ruiabreu
Joined: 15 Sep 2003
Posts: 12
Location: Portugal |
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Hi Ben
Here are the answers, sorry the delay. Maybe next week all do your questions first.
Describe each of the following methods of synthesis, and name one famous example/model of each:
a) Analogue
Analogue synthesis is a method used by non-digital synthesisers. The sounds are generated by triggering physical electrical oscillators. This synthesis can be subtractive or additive. Subtractive is the method most often used my analogue synthesisers and consists of generating sound waves with a wide range of harmonics and then removing certain frequencies trying to approximate the wave to that of a real instrument. Additive synthesis is less used and is the opposite of the subtractive synthesis. In this case we start with a simple sine wave with a certain frequency or pitch and then had other frequencies to try and emulate the harmonics of a certain instrument. An example of a substantive synthesiser is the Kawai K5000S.
b) FM Synthesis
FM stands for Frequency Modulator. In this method of synthesis there is an oscillator (carrier) that produces a signal. This signal is altered in a periodical manner with a second oscillator (modulator). The signal produced by the modulator is feed to the carrier. You can have more than one modulators. This type of synthesis can be of digital or analogue nature although the digital is most commonly used. Unlike additive synthesis, FM synthesis only produces sine waves.
c) Physical Modelling
Physical Modelling uses a different approach for emulating real instruments. In additive and FM synthesis you have an initial sound that is shaped using filters and modulators to approximate the sound to the real instrument. You only take in consideration the wave spectrum of the instrument but not how the instrument is physically played. With physical modelling you establish a process that models the physical instrument. When you play the instrument, you feed the synthesiser with parameters that put the physical model of the instrument.
d) Wavetable & S+S
In this type of synthesiser you use wave samples that are trigger by the keys from the keyboard. These samples are recorded in the synthesiser memory. In a wavetable synthesiser you usually have a small number of waves for instrument emulated. The pitches of these waves are altered according to the key played.
Define the following terms within the synthesis discipline;
a) Oscillators
These are electrical or digital devices that, when triggered, produce a certain sound wave with a certain shape and amplitude.
b) Filters
Filters are devices that cut off a certain frequency or frequency range. Usually they appear next to the main oscillator.
c) Envelopes and Amplifiers
Amplifiers are devices that control the amplitude of a wave produced by an oscillator usually after the signal has passed through the filter. An envelope is a specific type of amplifiers controller with a fixed number of steps. The best example of an envelope is an ADSR envelope.
d) LFOs
LFO (Low Frequency Oscillators) are modulator devices that change the characteristic of the sound over a period of time. These are a specific kind of oscillators that are mixed with the initial wave. You can modulate the fundamental frequency of the wave (vibrato), the amplitude of the wave (tremolo) or the harmonic content of the sound.
f) ADSR Curves
It´s a type of amplitude envelope. In this case the amplitude of the sound is carefully controlled. After the wave is triggered by the oscillator the amplitude rises rapidly (Attack) then it drops to a intermediary value (Decay) then it is maintained in that intermediary value (Sustain) and after sustain the sound drops to zero (Release). This envelope tries to emulate real instruments but you can have other types of envelopes producing more or less interesting sound depending on the musician.
Explain the following terms with reference to a synthesiser:
a) multitimbral
Multitimbral states the number of sounds a synthesiser can produce at the same time.
b) polyphony
Polyphone states the number of sound you can play at the same time by pressing the keyboard keys.
c) after touch
After touch is related to the time you spend pressing a key and the strength of that pressure.
d) on velocity
On velocity is a measure of the strength you use when hiting the keyboard key.
Arrange the following devices in the order they would normally be used for subtractive analogue synthesis:
a) VCO
b) VCA
c) VCF
VCO – VCF - VCA
FM Synthesis
a) What is an operator?
Operators are the name used in FM synthesis for oscillators.
b) What is a carrier?
It’s a type of oscillator or operator that is modulated by one or more modulators. Carrier is always the last oscillator of a sequence of oscillators, being the one that produces the sound that goes through the output.
c) What is a modulator?
In FM synthesis it’s a type of oscillator that sends a signal that modulates the signal of another operator. A modulator can modulate the sound of another modulator or the last operator in the chain, the carrier.
d) What is an algorithm?
In FM synthesis you can have more than 2 operators (usually 4 or 6). Algorithms control the combinations of operators you can have. The carrier is always the last oscillator.
How does a digital oscillator produce a waveform?
Couldn’t figure this out, but the bottom line result should not be very different from analogue oscillators (left no question answered).
How would a computer soundcard with onboard sounds usually generate its sounds?
Using wavetable and FM synthesis. These are easier to perform digitally.
Which types of synthesiser are most suited to which applications?
Synths
Analogue - 1960’s Sci-Fi film soundtrack
FM - 1980s synth pop music
Sample + Synth - Versatile ‘workstation’ keyboard
Wavetable - Tinkly electric piano sounds
Physical modelling - Emulation of acoustic instruments |
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Sun Sep 28, 2003 12:07 am |
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Fenderocks
Joined: 09 Aug 2003
Posts: 26
Location: Music City, USA |
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Describe each of the following methods of synthesis, and name one famous example/model of each:
a) Analogue- is the sounds that are made through electronic waveforms as opposed to digital or sample based synthesis. Tr808-tr909, no experience with any synthesizers, but I HEAR this is a good one.
b) FM Synthesis- is quite efficient in that it can create complex sounds from a few simple sine waves. Frequency modulation is, the output signal of one oscillator modulates frequency of another sailor. Yamaha dx synthesizers have come a long way.
c) Physical Modeling- this ones the odd ball, different to all other types of syths. This is a synthesis where you control what makes that sound, instead of making the sound; you can create any sound source. Model vl1 and vl1m
d) Wavetable & S+S- Based on actual sounds re-recorded of actual sounds and instruments. Change the pitch of any sound you have. Waldorf is a Wavetable syths.
Define the following terms within the synthesis discipline;
a) Oscillators- they provide the power waveforms which controls the shape and characteristics.
b) Filters – devices that allows you to take away certain components of a sound, depending on its frequency. Their cut off and resonance are its two specific sound sculpting tools.
c) Envelopes and Amplifiers- the envelopes are used for changing the shape of sound and the
Amps- are used to determine the overall volume of the signal routed from the oscillator.
d) LFOs –this stands for low frequency oscillators is a wave that repeats at a slow rate. There are many lfo’s and any one of those determines it’s frencencey of a waveform.
e) Velocity Zones-It controls the parameters of sound. The velocity zone are parameters to which individual sound have been set to. Using them you can recreate the response of the actual instrument. The higher the velocity, the higher the volume of the note is
f) ADSR Curves- control the decay, sustain, release, and attack of a given sound.
Explain the following terms with reference to a synthesizer:
a) multitimbral- when the synth can play more than one sound at a time
b) polyphony –polyphony is the number of notes that the synth can play simultaneous. This is usually set to the number of channel the unit has. On a 16 channel unit 64 note with polyphony, the synth can play 64 at a time, spread out over 16 different instruments
c) after touch- is when all the notes on a midi channel have the same volume.
d) on velocity – is when all the notes are preset, meaning when you hit notes they already has a designed setting.
Arrange the following devices in the order they would normally be used for subtractive analogue synthesis:
a) VCO VCO- Voltage controlled oscillator
b) VCA VCF – Voltage controlled Filter
c) VCF VCA- Voltage controlled amplifier
FM Synthesis
a) What is an operator? A carrier
b) What is a carrier? Is one of the two sinewaves
c) What is a modulator? This is the other sinewave and the modulating wave, changes the frequency of the carrier
d) What is an algorithm? The algorithm determines how each operator interacts with another, which is fed into another, or added to another.
How does a digital oscillator produce a waveform? The Vco or the Dco, these are the two types of oscillator. The Digital oscillators, is what produces waveforms at a certain frequency, and a digital component rather than a voltage generator control the oscillators.
How would a computer soundcard with onboard sounds usually generate its sounds? You need to turn one of the two settings off to allow one to rule.
Which types of synthesiser are most suited to which applications?
Synths
Analogue
FM
Sample + Synth
Wavetable
Physical modelling
Applications
1980s synth pop music -----------wavetable.
Versatile ‘workstation’ keyboard –sample synths
Emulation of acoustic instruments –physical modelling
1960’s Sci-Fi film soundtrack -------applications
Tinkly electric piano sounds---------analogue |
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Sun Sep 28, 2003 10:02 am |
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indigojf
Joined: 03 Aug 2003
Posts: 12
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I realize all of these answers I'm posting are horribly overdue, but there's not really much I can do about it at this point other than apologize and post my answers, so... Sorry. Here they are.
Describe each of the following methods of synthesis, and name one famous example/model of each:
a) Analogue
In analogue synthesis, a waveform is produced by an oscillator, then a filter is used to remove frequencies and what's left is sent to an an amplifier, which controls the volume of the sound over time. This method is called subtractive synthesis.
Example: Moog Prodigy
b) FM Synthesis
FM stands for Frequency Modulation. In FM Synthesis, the frequency of one oscillator (the carrier) is controlled by the output of another oscillator (the modulator), causing the pitch to rise and fall rhythmically.
Example: Yamaha DX7
c) Physical Modelling
Physical modelling synthesis uses equations and algorithms to simulate the actual physical sound of an instrument being played.
Example: Yamaha VL1
d) Wavetable & S+S
Wavetable synthesis uses a number of digital algorithms on a lookup table to shape the sound being played.
ExampleL Waldorf Wave
Define the following terms within the synthesis discipline;
a) Oscillators
Oscillators generate waveforms. The pitch of the sound is determined by the rate the oscillator generates each cycle of the waveform and is measured in hertz.
b) Filters
Filters remove frequencies of the waveform to alter its sound.
c) Envelopes and Amplifiers
Amplifiers use envelopes as guides for controlling the loudness of a sound over time.
d) LFOs
LFO stands for Low Frequency Oscillator. These act as modulators and can be used for many different effects.
e) Velocity Zones
Not sure on this one...
f) ADSR Curves
ADSR is the most common type of envelope. It has 4 components, which are Attack, Decay, Sustain, and Release. Attack is the amout of time it takes for a note to reach it's peak in volume. Decay is the amount of time in between the peak of volume and it's sustain level, which is the volume the note will remain at until the key is released. Release then, is the time it takes the sound to fully fade out once the key has been released.
Explain the following terms with reference to a synthesiser:
a) multitimbral
The ability to use more than one sound at a time. If you have a synthesizer that is 16 part multitimbral, that means you can play 16 different patches at a time.
b) polyphony
The ability to play more than one note at a time, and the deciding factor on how many notes can be playing at any one time.
c) after touch
The amount of pressure applied to a key once it has already been pressed down. This is used as a form of expression.
d) on velocity
Velocity is a value that represents the speed at which you push down a key. This can be used to control different forms of expression, but is generally used for volume. The higher the velocity, the higher the volume.
Arrange the following devices in the order they would normally be used for subtractive analogue synthesis:
a) VCO
b) VCA
c) VCF
The VCO, followed by the VCF, then the VCA.
FM Synthesis
a) What is an operator?
Operators are oscillators and can be set to be either a carrier or a modulator.
b) What is a carrier?
The carrier is an operator that produces the sound.
c) What is a modulator?
A modulator is an operator that changes the sound of other operators in the signal chain.
d) What is an algorithm?
Algorithms are preset combinations of routing operators. The carrier is always last in the chain and the rest are always modulators.
How does a digital oscillator produce a waveform?
The algorithm for a sine wave is stored in a table and accessed when a tone is requested. The waveform is controlled digitally.
How would a computer soundcard with onboard sounds usually generate its sounds?
Usually wavetable synthesis, but some cards use FM synthesis.
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
1980s Synth Pop music: FM, Analogue
Versatile ‘workstation’ keyboard: Sample + Synth
Emulation of acoustic instruments: Physical Modelling, Wavetable
1960’s Sci-Fi film soundtrack: Analogue
Tinkly electric piano sounds: Analogue, FM |
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Tue Nov 04, 2003 1:29 pm |
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