ben m
Joined: 15 Sep 2002
Posts: 337
Location: UK |
| Week 4 - Synthesis 1 |
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Ok, here are this weeks questions. Let's try to keep the quality of the answers as high as the previous couple of weeks.
Good Luck. 
 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 |
Tue Mar 30, 2004 6:31 am |
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griff505
Joined: 23 Feb 2004
Posts: 68
Location: Bristol |
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Damn that was fun!!!!
Describe each of the following methods of synthesis, and name one famous example/model of each:
a) Analogue - With analogue synthesis, the sound starts as an analogue signal, and is then processed by more analogue signal, before being issued from the Out socket (as opposed to digital synthesis where sounds are created as a series of numbers & processed, before finally being turned into an analogue signal). The first synthesizers were analogue, developed from various bits of electronic test equipment used in laboratories (signal generators, filters, etc) which were used to produce early electronic music. The equipment was developed and all the modules put into one large box (or a series of boxes), a means of connecting the modules together and a standard mechanism for controlling the modules were also developed. The result was the voltage controlled synthesizer. Originally synthesizers consisted of a large number of modules, which could be connected together in any way desired e.g. Modular Moog, Arp 2500 Modular System #1. Later, the key modules were put together in the one box, with a 'standard' connection hard wired in and a keyboard attached. These synths were less flexible than the big modular jobbies, but were a lot more portable and easier to use, e.g. Moog Minimoog, Korg MS-10, Octave CAT.
Analogue synths have the following:
- Keyboard - The device that is normally used to play the synth. When a key is depressed, the keyboard sends out an on/off signal, which includes trigger voltage and control voltage. The voltage depends on the key being pressed with each key has a unique voltage. This means the oscillator knows what pitch to sound for each key pressed.
- The Voltage Controlled Oscillator (VCO) - The module that actually produces sound is called the oscillator which produces a constant tone. The pitch of this tone is determined by the value of a control voltage sent from the synth's keyboard therefore if the voltage is varied various effects can be produced e.g. wobbling the control voltage up and down a little bit at a relatively low frequency (5 times a second / 5 'hertz') produce a vibrato. There are a number of standard waveforms: - sine, saw-tooth, square, noise.
- The Voltage Controlled Filter (VCF) - The filter shapes the tonal qualities (the bass & treble) of the sound. It works by removing, or at least greatly reducing, certain frequencies from the sound. It is effectively a powerful tone control. There are three types of filter - Low Pass (removes high frequencies from the sound), High Pass (removes the low frequencies from the sound) and Band Pass (a low pass & high pass filter combined - it filters out high and low frequencies to leave just a band of frequencies in the middle).
- The Voltage Controlled Amplifier (VCA) - Controls the volume of the sound. It's more than just a straight volume control though. Like the VCO & VCF it can be controlled by a voltage dynamically. It can be controlled by an envelope generator to shape the loudness contour of the sound. We can use the VCA (and envelope generator) to control whether a sound starts instantly when a key is pressed, or builds up gradually. It is also used to control how the sound dies away (quickly or slowly) when a key is released. It is usually only an envelope generator that controls the VCA, as well as some of the output of the LFO.
- The Envelope Generator - The envelope generator doesn't produce any sound itself, or even process another sound directly. It produces a control voltage output when it receives a trigger signal from a key press. This control voltage can be fed to the VCA to control the 'shape' of the sound. It can also be fed to a VCF to determine how the sound's tone changes. A good envelope generator has 4 sections: Attack, Decay, Sustain, and Release. These each determine what happens at certain points during a note.
- The Low Frequency Oscillator (LFO) - The LFO produces a signal with a relatively low frequency; it may range from 1 cycle a minute up to maybe 10 times a second (10 Hz). The waveform is usually a sine or triangle wave, though some synths let you vary this. The LFO is not used to generate a signal that you can hear, but is used to modulate the other parts of the synth to generate effects.
b) FM Synthesis - FM techniques have been around since the early twentieth century, and by the 1930s FM radio broadcasting was well-documented and understood. In the 1970s FM was thoroughly researched as a musical synthesis tool. John Chowning, a composer and researcher at Stanford University, developed some important new techniques for music synthesis using FM. In the early 1980's the Yamaha Corporation introduced their extremely popular DX line of FM synthesizers, based on Chowning's work. The DX-7 keyboard synthesizer was the top of their line.
FM turned out to be good for creating a wide variety of sounds, although it is not as flexible as some other types of synthesis. It's simple, easy to understand, and allows users to tweak just a few knobs to get a wide variety of sonic variation.
In its simplest form FM involves two sine waves, the modulating wave, and the carrier wave. The modulating wave changes the frequency of the carrier wave. Both the modulator and the carrier are periodic or quasi-periodic oscillators with characteristic frequency, amplitude, and wave shape:
- The frequency of the modulator affects the rate of change of the carrier’s frequency.
- The amplitude of the modulator affects the degree or depth of change of the carrier’s frequency.
- The shape (or timbre) of the modulator affects the shape of change of the carrier’s frequency.
- The amplitude of the carrier is not changed.
FM can create vibrato when the modulating frequency is less than 30 Hz. If we raise the frequency of the modulating oscillator above 30 Hz we can start to hear more complex sounds. We can make an analogy to being able to see the spokes of a bike wheel if it rotates slowly, but once the wheel starts to rotate faster a visual blur starts to occur. When the modulating frequency starts to speed up, the sound becomes more complex. The tones can be heard sliding around; these are called sidebands, and are extra frequencies located on either side of the carrier frequency. Sidebands are the secret to FM synthesis. The frequencies of the sidebands as a group are called the spectra. Chowning, in a famous article, showed how to predict where those sidebands would be by using a simple mathematical idea called Bessel Functions. By controlling that ratio (called the FM index), and using Bessel functions to determine the spectra, you can create a wide variety of sounds, from noisy jet engines to a sweet sounding Fender Rhodes.
c) Physical Modelling - Physical modelling synthesis is the method of creating audio with a numerical model of a physical system. What makes it distinct is that a modelling synthesis algorithm attempts to embody the characteristics of real instruments, using a model motivated by a physical analysis of the system. We can loosely think of modelling synthesis as a 'predictive' sound synthesis method, because the sound is generated in a way that refers to the actual physical response of the system. The user is actually creating and controlling a process that produces that sound.
The strength of physical modelling is that the parameters involved are easy to understand because they have a real counterpart. For example, when trying to create a horn sound that has the variation in spectral content found when a horn is played with different strengths. It would be very hard time figuring out which parameters to change in an FM synthesis algorithm. With a good physical model and a wind controller, all you have to do is blow harder, and the sound produced will respond to the playing level. Physical modelling is quite flexible and a single algorithm can achieve a variety of sounds, without requiring more memory. Wavetable based synthesizers require a number of samples (with each sample taking up some amount of memory) at different registers to be able to produce realistic sound of a single instrument. But a single physical modelling algorithm can be capable of producing a full range of sounds simply by adjusting the input parameters. E.g. KORG Z1, Yamaha's VL1 / VL1m.
d) Wavetable & S+S – Wavetable synthesis takes samples of musical instrument sounds such as a violin and digitises the sound and stores it in a memory chip. Samples capture the attack, decay and envelope shape of each instrument and incorporate looping to maintain long notes. On some patches you can even hear the bow striking the string. E.g. Roland RS-50, Creative Labs Sound Blaster PCI Card.
Define the following terms within the synthesis discipline;
a) Oscillators – An Oscillator continuously generates a waveform or shape which become a sound. The rate at which it generates each cycle of the waveform is what we hear as pitch ( 1 Hertz = one cycle per second ). On a synth the keyboard-controlled oscillator may be labelled VCO, DCO, or Waveform. When a key on the synth is pressed, the oscillator will generate the waveform at the intended pitch continuously. The most common waveforms are sine, triangle, pulse, square and saw tooth.
b) Filters – A filter is used to remove frequencies from the waveform to alter its timbre. On a synth it may be labelled VCF (voltage controlled filter) or DCF (digitally controlled filter) and may include:
- Low Pass Filter – Allows lower frequencies to pass through unaffected and filters out higher frequencies.
- Cut Off – Determine the point in the harmonic spectrum where the filter will begin to filter the higher harmonics.
- Resonance – Boosts frequencies at the cut off point, when set at a high level the filter itself will start to self-oscillate (a controlled feedback).
- High Pass Filter – Allows higher frequencies to pass through unaffected and filters out lower frequencies.
c) Envelopes and Amplifiers – The amplifier section on a synth is sometimes labelled VCA (voltage controlled amplifier). It uses an envelope to control the overall loudness of the sound over time, usually using 4 parameters:
- Attack – The attack time controls the length of time it takes from pressing a key on the synth until the envelope opens to its fullest. Increasing the attack time will make this process happen more slowly.
- Decay – With the key still pressed the envelope drops from full to the sustain level. The decay setting controls the length of time this takes. Increasing the decay time will make this happen more slowly.
- Sustain – This level controls the volume produced while the key is held pressed.
- Release – The release value sets the amount of time the volume takes to return to zero from the sustain level once the key has been released. A value of zero means this will happen instantly.
d) LFOs – Low Frequency Oscillator – A very common oscillator found on most synthesisers which oscillates between 0.1 Hz and 10 Hz. An LFO usually has a number of parameters: Wave, Rate and Delay (the time before which an oscillator starts. Usually sine or tri waves are used as they provide smooth rises and falls without sudden jumps, although square and saw waves can be used for special effects. The LFO can be assigned to modulate the Oscillator Pitch, The Filter Cut-Off, or the VCA.
e) Velocity Zones – A Wavetable synth or sampler can be set up so that a particular zone of the keyboard triggers different samples depending on the velocity assigned to that zone. For example a piano setting may be programmed to trigger a string sound as well as the piano sound if the velocity exceeded a velocity of 90.
f) ADSR Curves – An ADSR curve is the outline created by the envelope settings of Attack, Decay, Sustain, and Release.
Explain the following terms with reference to a synthesiser:
a) Multitimbral - A multi-timbral synthesizer is an instrument that has the ability to play 2 or more different sounds at the same time. The number of multi-timbral parts refer to the number of different sounds it can playback simultaneously. A typical multitimbral tone generator can play, for example, the brass, piano, and violin parts all at once. For example, a Kurzweil K2500 is 16-part multitimbral, meaning it can produce 16 different sounds at once (a sound being defined as a single patch or preset; part one might be piano, part two strings, part three trombone, part four flute, and so on. Generally these parts are assigned to different MIDI channels for independent control). This is distinct from the amount of polyphony, or number of actual notes the unit can simultaneously generate.
b) Polyphony – Polyphony means many-sounding, on a synth it refers to the number of notes of a particular timbre that can be played and sounded at once. If the polyphony of a synth was 4 and a fifth notes was played one of the other notes would be cancelled out. A synth for playing bass lines can be monophonic, however a synth trying to replicate a piano needs to be polyphonic.
c) After touch – This is additional information sent to a sound module after the key has been pressed usually to control vibrato, volume, and other parameters. MIDI data is sent when pressure is applied to a keyboard after the key has been struck, and while it is being held down or sustained.
d) On velocity – This is based on the working of a piano whereby the volume produced by the instrument is dependant upon the velocity the key is pressed. On Velocity replicates this by assigning a MIDI value of between 0 and 127 to determine the volume of the sound generated when the key is pressed at a certain velocity.
Arrange the following devices in the order they would normally be used for subtractive analogue synthesis:
a) VCO
b) VCA
c) VCF
VCO -> VSF -> VCA.
An Oscillator is used to generate a suitably bright sound. This is routed through a Filter which cuts-off or cuts-down the brightness to something more suitable. This resultant sound is routed to an Amplifier which controls the loudness of the sound over a period of time so as to emulate a natural instrument. Therefore you start with a sound, subtract out the unwanted bits and control its loudness over time.
FM Synthesis
a) What is an operator? – This is an oscillator, and it either produces the sound source or shapes the sound source depending on whether it is set as a carrier or modulator.
b) What is a carrier? – The oscillator which is being modulated. The pitch of the Carrier is being changed (modulated) in tandem (in sync/ going up and down at the same time) by the Modulator.
c) What is a modulator? - The frequency of the oscillator which modulates the Carrier
d) What is an algorithm? - Algorithms are the preset combinations of routing available to you. Carriers are always the last Operators in any Algorithm chain and all other Operators are Modulators.
How does a digital oscillator produce a waveform?
- Digital Oscillators produce a waveform at a certain frequency. A digital component rather than a voltage generator controls the oscillators. However in a Digitally Controlled Oscillators (DCO) the actual waveforms are generated in the usual analog way. The oscillator’s frequency can be manipulated by modulation of another oscillating signal to determine a different pitch or frequency. It can produce a sine wave or even tone of that frequency. It can also produce a specific waveform such as saw sine tooth triangle etc.
How would a computer soundcard with onboard sounds usually generate its sounds?
- Using Wavetable, FM Synthesis or Physical Modelling. FM synthesis simulates sounds 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. Wavetable uses actual, digitally recorded sound samples stored on the card for the highest performance. Physical modelling is a new type of synthesizing, in which sounds are simulated through a complex programming procedure. Some sound cards can also have sounds downloaded to them.
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 - Tinkly electric piano sounds
Wavetable - Versatile ‘workstation’ keyboard
Physical modelling - Emulation of acoustic instruments |
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Wed Mar 31, 2004 11:52 pm |
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hoggs33
Joined: 09 Feb 2004
Posts: 55
Location: Nottingham, England |
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Describe each of the following methods of synthesis, and name one famous example/model of each:
a) Analogue - This was the first type of synthesis available to the ‘consumer’. Analogue synthesis works by taking electric currents and changing it into sound by using voltage control oscillators (VCO’s). The Mini Moog is a famous example which had three oscillators, one could layer three electronic currents, each within it’s own envelope, and a filter over the entire sound.
b) FM Synthesis – This is Frequency Modulation Synthesis which began in 1983 with the introduction of the Yamaha synthesizers. The first type of FM synthesis involved taking a sine wave, and modulating it with other sine waves to create a more complex wave form. The next generation allowed the user to select eight different complex wave forms and modulate it with another complex wave form. This type of synthesis was found on units such as the TX81Z and V50. This type of synthesis is often called selectable wave synthesis. The third type of FM synthesis is called Advanced Frequency Modulation Synthesis (AFM). This allows the user to take a sample from the internal of the keyboard, input it into the FM formula and create a new sound. This FM also contains sine waves and selectable waves.
c) Physical Modelling – Physical Modelling does not create a sound directly – with physical modelling you are creating and controlling a process that produces the 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. It grew out of research into mathematical models which describe the physics of sound generation in acoustic instruments. It represented a radical departure from all previous synthesis techniques as it is neither additive nor subtractive, it does not treat the synthetic waveform simple as frequency or time-domain components and it bridges the gap between analogue or FM synthesis and sampled ‘real’ instruments. An example is the Yamaha VL1
d) Wavetable & S+S - the S + S stands for Sample + Synth. It is a technique that uses sampled sound representations of instruments as the basis of its sound generation process, but does not need to sample every note played in every possible way. An example is the Roland RS-50.
Define the following terms within the synthesis discipline;
a) Oscillators – An oscillator is the main sound source in analogue synthesizers and software emulations. Oscillators generate sound by oscillating surprisingly enough. In other words their circuitry changes or oscillates, between two states very quickly, and just as a vibrating string produces a sound, so the oscillating electronic circuit generates a waveform that can be amplified and used as a sound source.
b) Filters – Filters are used to remove frequencies from a waveform so as to alter the timbre.
c) Envelopes and Amplifiers – Envelopes are controllers, most of which are separated into four sections – attack, delay, sustain and release. Amplifiers act as volume controls, allowing a sound to differ in volume.
d) LFOs – These are Low Frequency Oscillators and are controlling oscillators. LFO’s operate below the sound spectrum, usually completing a cycle any time from ten seconds to 1/100th of a second.
e) Velocity Zones – velocity controls the playing parameters of sounds for example info relating to how hard you press down on a key when you initially strike it is velocity. The velocity zones are the parameters to which individual sounds have been set to.
f) ADSR Curves – these control the attack, delay, sustain and release of a given sound
Explain the following terms with reference to a synthesiser:
a) multitimbral a multitimbral synthesizer is an instrument that has the ability to play 2 or more different sounds at the same time. The number of multi-timbral parts refer to the number of different sounds it can play back at the same simultaneously.
b) polyphony - the number of notes or keys that can be played back at the same time.
c) after touch – a means of generating a control signal based on how much pressure is applied to the keys of a midi keyboard. After touch may be used to control functions such as vibrato depth, filter brightness, loudness etc.
d) on velocity – this emulates the weight that a key was pressed – the harder you press, the louder the sound such as on a piano. On a MIDI keyboard the velocity range is usually 1 to 127 with 1 being the quietest and 127 being the loudest.
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? – isn’t it something off The Matrix?!!!!!! (sorry). An operator is basically an oscillator. An FM synth will have either 4 or 6 operators because the sounds from one modulator and one carrier are not very good.
b) What is a carrier? – The carrier is the frequency of the oscillator which is being modulated
c) What is a modulator? – The frequency of the oscillator which modulates the carrier
d) What is an algorithm? – Algorithms are the preset combinations of routing available to you
How does a digital oscillator produce a waveform? – digital oscillators produce a signal waveform at a certain frequency. A digital component rather than a voltage generator controls the oscillators – not really sure on this one – struggled to find much info.
How would a computer soundcard with onboard sounds usually generate its sounds? – By FM or 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 - FM
Versatile ‘workstation’ keyboard – Sample + synth
Emulation of acoustic instruments – Physical modelling
1960’s Sci-Fi film soundtrack - analogue
Tinkly electric piano sounds - Wavetable |
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Fri Apr 02, 2004 5:58 pm |
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iNSTiNCT2765
Joined: 05 Nov 2003
Posts: 60
Location: Denmark |
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Week 4 - Synthesizers 1
Describe each of the following methods of synthesis, and name one famous example/model of each:
a) Analogue – the first types of synthesizers made were analogue. The sound produced is an analogue signal that is processed with more analogue signals before it is output. The three main components in an analogue synth is a voltage controlled oscillator (VCO), a voltage controlled filter (VCF) and a voltage controlled amplifier (VCA). An example is the Korg MS2000.
b) FM Synthesis – Frequency modulation is done by changing the frequency of a signal rapidly and repetitiously. This is done with the use of a second signal called the ‘oscillator’. This signal modulates the frequencies of the first signal called the ‘carrier’. The Yamaha DX7 FM synth is a good example of this.
c) Physical Modelling – this is a way of emulating acoustic instruments using mathematical algorithms. The physics of the instrument and its playing techniques are modelled by a computer. An example of this is the Yamaha AN1x synthesizer.
d) Wavetable & S+S (sample + synth) – this is a way of generating sound using digital signals by storing samples of different instruments. The samples can then be combined, edited and enhanced to produce sound. Korg Triton is an example of a Wavetable synth.
Define the following terms within the synthesis discipline:
a) Oscillators – the oscillator produces the tone or sound.
b) Filters – shapes the tonal qualities of the sound produced by the oscillator. The way it works is by removing certain frequencies from the sound.
c) Envelopes and Amplifiers – the envelopes control the attack, decay, sustain and release of the sound that is generated. This can change the volume characteristics of the sound by changing the time it takes the sound to reach full level, how long it takes to die down etc.
d) LFOs – The low frequency oscillator is the most commonly used filter and works by removing the high frequency of a sound progressively.
e) Velocity Zones – Different zones set out so the sound varies in volume depending on how hard you press down the keys on a keyboard when you trigger the sound. Since an instrument may sound differently not just in volume but also in some of its characteristics when played softly, this is emulated in most modern sound modules.
f) ADSR Curves – these are attack, decay, sustain and release settings working together to produce an envelope that affects the sound.
Explain the following terms with reference to a synthesiser:
a) multitimbral – this means that the synthesizer can play more than one of the sounds in it at the same time. This is useful when using a synthesiser with a computer sequencer because via midi, 16 channels of different sounds can be played together to form a composition.
b) polyphony – the amount of polyphony a synthesiser has determines the number of notes that can be played simultaneously. If you have 32 note polyphony then you can press down 32 keys on your keyboard at the same time and all of them will play, if you press a 33 key, it will cancel out of one the other notes or not play before a key is released.
c) after touch – this means that a control can be generated depending on how hard the keys on the keyboard are pressed.
d) on velocity – determines how hard the keys are pressed on a midi keyboard?!?!?
Arrange the following devices in the order they would normally be used for subtractive analogue synthesis:
a) VCO
b) VCA
c) VCF
The VCO produces the tone and is then fed into the VCF, which colours the sound by adding filters and then the tone is sent to the VCF.
FM Synthesis
a) What is an operator?
This is an oscillator.
b) What is a carrier?
This is the signal being affected by the modulator.
c) What is a modulator?
This is the signal affecting the carrier
d) What is an algorithm?
This is a preset of a combination of operators you use to form FM Synthesis. The last operator is always a carrier and the rest are modulators.
How does a digital oscillator produce a waveform?
It produces a waveform using a DCO (digitally controlled oscillator) instead of a VCO. The pitch is very stable and doesn’t suffer from the tuning problems that the VCO may be experience.
How would a computer soundcard with onboard sounds usually generate its sounds?
The best way for a soundcard to generate sound is through the Wavetable approach since the card can then hold actual sampled sounds instead of having them sound a bit unnatural. Of course, the quality of the sounds would depend on the type of soundcard and probably the price too.
Which types of synthesiser are most suited to which applications?
Synths
Analogue
FM
Sample + Synth
Wavetable
Physical modelling
Applications
1980s synth pop music – FM
Versatile ‘workstation’ keyboard – Sample + Synth
Emulation of acoustic instruments – Physical modelling
1960’s Sci-Fi film soundtrack - Analogue
Tinkly electric piano sounds - Wavetable |
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Sat Apr 03, 2004 12:08 am |
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albertom
Joined: 21 Jan 2004
Posts: 22
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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
Analogue Synthesis - Analogue Synthesis is making sounds from electronic waveforms as opposed to digital or sample based synthesis.
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.
Physical Modelling - Physical modelling is 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.
Wavetable S + S - Wavetable synthesis is based on recordings of actual sounds and instruments to produce sound. It lets us create a digital sample and change it altering the pitch. Its a very good method of producing much more accurate sounds.
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 allow 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 specializes 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. It’s an essential parameter for any filter although it doesn’t 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. Envelopes are very good at replicating how sounds change over time, 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.
d) LFOS - Low Frequency Oscillators is a wave that repeats at a slow rate. There are many different shaped Lfos and each one determines the frequency of a waveform. The most common Lfo, waveforms are
Sine - is a smooth waveform and the pitch would also be smooth.
Sawtooth – is very good 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 suddenly change from one pitch to another.
Triangle – this waveform produces a soft modulation curve that contains all overtones. Its sound is closer to a sine than a Sawtooth wave.
e) Velocity Zones
Velocity controls the playing parameters of sounds. The velocity zones are the parameters to which individual sound have been set to. By using velocity zones you can recreate the response of the actual instrument.
ADSR Curves
ADSR Curves control the Attack. Decay, Sustain, and Release of a given sound. Useful for giving a sound variety character from the moment the sound is pressed to the moment its released.
Explain the following terms with reference to a synthesizer:
a) multitimbral
b) polyphony
c) after touch
d) on velocity
Multitimbral - is when the synth can play more than one sound at a time.
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 - is when synthesizers 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
The VCO produces the tone and is then fed into the VCF, which colors the sound by adding filters and then the tone is sent to the VCF.
FM Synthesis
a) What is an operator?
Is an oscillator.
b) What is a carrier?
Is the signal being affected by the modulator.
c) What is a modulator?
Is the signal affecting the carrier
d) What is an algorithm?
Is a preset of a combination of operators you use to form FM Synthesis. The last operator is always a carrier and the rest are modulators.
How does a digital oscillator produce a waveform?
Digital Oscillators produce a waveform at a certain frequency. A digital component rather than a voltage generator controls the oscillators. However in a Digitally Controlled Oscillators (DCO) the actual waveforms are generated in the usual analog way. The oscillator’s frequency can be manipulated by modulation of another oscillating signal to determine a different pitch or frequency. It can produce a sine wave or even tone of that frequency.
How would a computer soundcard with onboard sounds usually generate its sounds?
Using Wavetable, FM Synthesis or Physical Modeling. FM synthesis simulates sounds 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. Wavetable uses actual, digitally recorded sound samples stored on the card for the highest performance.
Which types of synthesizer are most suited to which applications?
Synths
Analogue
FM
Sample + Synth
Wavetable
Physical modeling
Applications
1980s synth pop music – FM
Versatile ‘workstation’ keyboard – Sample + Synth
Emulation of acoustic instruments – Physical modeling
1960’s Sci-Fi film soundtrack - Analogue
Tinkly electric piano sounds – Wavetable |
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Thu Apr 29, 2004 1:39 am |
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