ben m
Joined: 15 Sep 2002
Posts: 344
Location: UK |
| Week 4 - Synthesis 1 |
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I'm posting these early this week as I won't be around for tonights workshop or monday (at least til the evening)
I'll leave any required feedback on the Computers 2 thread on Mon night/Tue.
Here are the questions for Synthesis 1;
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 |
Sun Mar 27, 2005 9:04 am |
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JohnA
Joined: 20 Jan 2005
Posts: 28
Location: Mid Glamorgan, UK |
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Audio Course
AUMT03
Week 4
Synthesis
JohnA (mixindown)
Describe each of the following methods of synthesis, and name one famous example/model of each:
a) Analogue:
In analogue synthesis (or subtractive synthesis), you start with more sounds than you need and keep taking bits away until you end up with the sound that you want. It is essentially a 3-stage process:
a. Tone generation,
b. Tone shaping,
c. Volume shaping.
The tone or raw sound is generated with an “oscillator”, the tone is then fed into and through a “filter” which shapes or “colours” the sound. This is then fed into an amplifier. This amplifier is controlled by an envelope generator which allows control of the Attack, Decay, Sustain and Release of the generated tone. An oscillator is a device that generates waveforms of various shapes. Older synths were able to generate regular or cyclic waveforms such as sine, triange, square and sawtooth waveforms. Today, computer based oscillators can generate far more waveforms.
Hartley Oscillator is one famous model.
b) FM Synthesis
FM Synthesis (Frequency Modulation Synthesis) takes sine waves and multiplies them together in an attempt to generate complex waveforms more quickly. It tends to add several of these products together to get to its more effective results (which is why 6-operator FM sounds better than 4-operator FM, because you can add more products together). Invented by John Chowning.
c) Physical Modelling: Karplus-Strong
Physical Modelling is neither additive or subtractive. It is a method of creating audio with a numerical model of a physical system. Physical modelling synthesis is the synthesis of sound by using a set of equations and algorithms to simulate a physical source of sound. When an initial set of parameters is run through the physical simulation, the simulated sound is generated. For example, to model the sound of a drum, there would be a formula for how striking the a drumhead injects energy into the formula that describes the resonance and damping of the drumhead. Another formula could then be applied to mimic the separate resonance of the cylindical body of the drum.
d) Wavetable & S+S (Sample and Synthesis): Andrew Horner:
Wavetable synthesis is used in digital musical instruments (synthesizers) to produce natural tone-like sounds. The sound of a existing instrument (a single note) is sampled and parsed into a sequence of wavetables having one period or cycle in each wavetable. Upon playback, these wavetables are used for sample "lookup" in the same manner as in a Numerically-controlled oscillator (or a Digitally controlled oscillator) but in wavetable synthesis, the output waveform is not normally static and evolves slowly in time as one wavetable is mixed with another, creating a changing waveform. Looping occurs when the wavetable evolution is halted, slowed, or reversed in time.
Define the following terms within the synthesis discipline;
a) Oscillators
A device or electronic circuit that generates an RF (radio frequency) signal that generates a specific tone or frequency. It contains a path whereby the output signal is fed back into the input making it a continuous tone. The rate at which it generates each cycle of the waveform is what we hear as the pitch, measured in Hertz (Hz). One Hertz is one cycle per second. Although there are many types of oscillator, the main one is the Keyboard Controlled Oscillator, labeled on a synthesizer as VCO, DCO or sometimes as a Waveform.
b) Filters
A filter is a device that shapes the tone generated by the oscillator. In subtractive synthesis, a filter is used to remove frequencies from the waveform, to alter its timbre.
c) Envelopes and Amplifiers:
Once you've got a basic signal coming from your oscillator, you will need to amplify it in some way in order to make it audible. In analogue modular synths, Amps are used to convert a voltage into audible sound. We want some way of controlling the loudness of a sound.
An envelop will control the way in which the loudness of the signal changes over time. This will have an enormous effect on the quality of the sound, and is one of the most important factors in determining the eventual output of the synth. If you compare the sound of different instruments (or of any sound in fact) one of the many distinguishing factors is the way in which the volume of the sound changes over time. For example, think of the difference between a church organ which reaches its maximum volume almost instantaneously, compared to, say a violin, where there will be a slight delay before the note reaches full volume.
LFOs
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. The output of the LFO is usually fed to a Modulation Wheel before going to the oscillator. This allows you to control the vibrato level in real time - great for solos.
Lower frequencies and more modulation can be used to give siren type effects.
d) Velocity Zones
With velocity, the harder you press the key on a keyboard, the louder the sound becomes. Take velocity on a scale of 0 to 127 where 0 is not touching the key and 127 produces the loudest sound when you press the key. You can assign a sampled sound to velocity values 0 to 50, and assign a different sampled sound to values 51 to 127. When you press the key, if you press it so that the value is at 50 or below, you will just get the first sound, but if you press it at 52 or above, you will get the second sound.
f) ADSR Curves (Attack, Decay, Sustain, Release).
When a key on a keyboard is pressed:
Attack: time determines the speed at which the sound reaches its maximum loudness
Decay: time determines the speed at which the loudness drops until it reaches the…
Sustain: level, the level the loudness maintains until it decays to its final level (usually silence) in a time determined by the….
Release: time it will take the envelope to return to zero after the key has been released.
Explain the following terms with reference to a synthesiser:
a) multitimbral
A MIDI instrument can sometimes be referred to as being "multitimbral". It means that the midi device is capable of playing back on all 16 MIDI channels simultaneously, whilst playing any of it's instrument sounds or patches simultaneously, letting each instrument sound or patch play on a separate MIDI channel.
b) polyphony
Polyphony refers to the number of voices or, in most cases, instrument sounds a sound module, sampler, synth or midi device can play back at any given time. Most modern MIDI sound modules and samplers are capable of playing back at least 32 monophonic tones at once. Higher end modules allow up to 128 voices to be played at once. For example, if you use all of your fingers to press down 10 keys on your keyboard, you are using 10 voices of monophonic polyphony. However, if the instrument sounds (or samples) are in stereo, you are using 20 voices of stereo polyphony.
c) after touch
Aftertouch is a control that allows parameters of a synth (typically, filter cutoff, vibrato, volume etc.) to be controlled by how hard a key is pressed after hitting it and holding it.
d) on velocity
This applies to the attack of the note. On velocity or Note On velocity is when a key on a keyboard is depressed (pressed down). This information is sent down the midi cable to the sound source.
Arrange the following devices in the order they would normally be used for subtractive analogue synthesis:
a. VCO (Voltage Controlled Oscillator)
b. VCF (Voltage Controlled Filter)
c. VCA Voltage Controlled Amplifier)
FM Synthesis (FREQUENCY MODULATION SYNTHESIS)
a) What is an operator?
Operators are Oscillators. The basic 'building block' of FM synthesis is called an operator. This consists of an oscillator (traditionally a sine wave, but other waveforms are sometimes used), a DCA to control its output, and an envelope to control the DCA (Digitally Controlled Amplifier). But the most important aspect is that the oscillator has a control input to vary its frequency. Algorithms are the preset combinations of routing available to you. Note that the Carriers are always the last Operators in any Algorithm chain and all other Operators are Modulators.
b) What is a carrier?
Feeding one operator's output into another operator's control input creates complex modulations that generate 'side-band' frequencies. The operator being controlled is called the Carrier, the one doing the modulation is called the modulator. The sideband frequencies are mathematically related to the modulator and carrier frequencies.
What is a modulator?
It is a signal that controls or modulates another signal.
MODULATOR ------> CARRIER -------> sound output
d) What is an algorithm?
Algorithms are the preset combinations of routing available to you and are always the last Operators in any Algorithm chain and all other Operators are Modulators.
How does a digital oscillator produce a waveform?
A lot of digital synthesisers use samples of acoustic instruments to produce the sound. These samples have usually been recorded at different pitches. When you press a key on the keyboard controlling the samples, the synthesiser recalls the sampled audio data that is in the file memory. It then shifts it to the correct pitch, represented by the key that was pressed. This “raw sound”, because it is digital, is nothing more than a set of mathematical equations). So this then forms the raw sound that the filter and envelope act upon. This is the way that synthesisers can be used to create more realistic emulations of acoustic sounds than analogue synths can.
How would a computer soundcard with onboard sounds usually generate its sounds?
The soundcard would use either FM, Wavetable or Physical Modeling synthesis to generate its sound. These sounds are stored on a sound-chip on the soundcard. If you connect, for example, a midi keyboard (controller) to the souncard via its midi input, you can then use the keyboard to generate the sounds on the soundcard chip to be played via its outputs.
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 :Emulation of acoustic instruments
Physical modelling: Tinkly electric piano sounds
http://www.computermusic.co.uk/tutorial/a_sforbeg/a_sforbeg.asp
http://www.soundonsound.com/sos/jul99/articles/synthsecrets.htm
http://www.geocities.com/SunsetStrip/Underground/2288/2ansynth.htm#Basic
http://www.geocities.com/SunsetStrip/Birdland/3547/analog.htm
http://www.soundonsound.com/sos/1997_articles/jun97/synthschool1.html
http://www.soundonsound.com/sos/1997_articles/jun97/synthschool1.html
http://www.soniccontrol.com/tech/midi/faq/polyphony/
http://www.soundonsound.com/sos/nov03/articles/qanda.htm
John A |
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Fri Apr 01, 2005 2:47 pm |
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rachelh
Joined: 16 Jan 2005
Posts: 35
Location: Trinidad WI |
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Week 4 - Synthesis 1
Submitted by:
Rachel H, reynola 31.
1. Describe each of the following methods of synthesis, and name one famous example/model of each:
a) Analogue
The term ‘Analogue Synthesis’ describes the technology by which controlled voltage analog modules are used to create the synthesiser sound. This system uses a variety of analog of modules which all interconnect with the use if a standardised voltage control system. The three main voltage controlled modules in an analog synthesizer are: Voltage Controlled Oscillator (VCO), Voltage Controlled Filter (VCF), and Voltage Controlled Amplifier (VCA). The oscillator generates a periodic waveform, the filter is usually employed to remove certain frequencies from the waveform, and the amp is used to vary the attack and decay characteristics of the waveform.
[1][2]
b) FM Synthesis
The term FM synthesis or namely Frequency Modulation Synthesis describes the technology whereby sounds were generated via the use of an analog synthesiser. The sounds generated being complex signal waveforms, generated of one or more sine wave signals by other sine waves. Pioneered by John Chowning, FM synthesis allows for a wide variety of waveforms to be created. FM (frequency modulation) is based around using the frequency of one signal (the modulator) to change the frequency of another audible signal (the carrier). Compared to additive synthesis, FM requires significantly less hardware. One example of a FM synthesiser is the Yamaha DX-7, this keyboard, ‘brought FM synthesis to the masses and it is still renowned for its pure bell like times and electric piano sounds’ [1].
[1][2]
c) Physical Modelling
Physical Modelling Synthesis relates to a type of sound synthesis whereby the synthesis itself is performed via computer models of actual instruments. These models are sets of complex equations that describe the physical properties of an instrument (such as the shape of the bell and the density of the material) and the way a musician interacts with it (blow, pluck, or hit, for example). [2]
d) Wavetable & S+S
Wavetable synthesis is a method of synthesis whereby waveforms are generated by loading their characterises from a special set of parameters stored in a look up table into read only memory chips. Although small, the memory allows for various sample based synthesis techniques to be implemented such as mathematical interpolation, pitch shifting and digital filtering which all create richly textured sounds. An example of a Wavetable is the Yamaha SY22. [2]
2. Define the following terms within the synthesis discipline:
a) Oscillators
An oscillator is an electronic device, which generates a periodic signal of a particular frequency. Sine saw tooth as well as triangle waves are used to generate these signals. Sometimes, a second oscillator is forced to synchronise with another [oscillator sync], this produces a sound that is characteristically animated and change over time such as many synth patches. Early synthesizers used oscillators as the basic component for all of the sounds of the machine. All of the filters and envelopes modified the sound created by the oscillator to produce the desired sound. Nowadays most keyboards produce sounds by playing back samples recorded on chips or by more modern synthesis techniques such as Physical Modelling, Frequency Modulation or any number of other methods that have been employed in the past 10 years. [2]
b) Filters
A filter is an electronic device designed to reduce a signal's energy at a specific frequency. A true filter always acts as a subtractive device, not adding anything to the signal. In synthesisers, filters are used to modify the sound created by the oscillator and produce the desired sound, of course without adding anything to the signal. The filter can also be used to reduce the inherent noise and distortion created by the amplifier [VCA]. [2]
c) Envelopes and Amplifiers
An electronic amplifier is a device for increasing the power of a signal. In synthesisers, the Voltage Controlled Amplifier [VCA] is currently used to create the volume envelope of sounds, the VCA being an amplification circuit whose gain is controlled by an external voltage source. This envelope of which we refer is the variation that a sound exhibits over time - basically how a sound starts, continues and disappears. It is comprised of concepts such as attack and decay, but other sonic distinctions such as transient and sustain may also be applied in some circumstances. Pitch, timbre and harmonic content (which is basically timbre) can also change over time and in some cases are considered part of the overall envelope making up a sound. An envelope generator [EG] sometimes called a transient generator is a circuit or algorithm is found in most synthesizers and provides a means to apply these kinds of changes to a sound over time. VCAs are also commonly found as the level attenuation devices in compressors, companders and limiters. [2]
d) LFOs
An oscillator is an electronic circuit, which produces periodic or regularly repeating waveforms; i.e. sine, square, sawtooth, or triangle waves. An LFO is an oscillator producing these waveforms at a very low frequency or pitch. LFO’s are used to modulate or to change a parameter of a synth, they are primarily used as modulators for other things. These generally subsonic, slowly vibrating waves are in the 0 - 20 Hz range or thereabouts, although they may not exclusively operate in that range. ‘One common application is modulating the pitch of an audio oscillator with an LFO; this results in vibrato. If the volume of an audio oscillator is modulated with an LFO, the result is tremolo. Just about any time you see a "modulation" control on a device, it is controlling an LFO, and being used to periodically change some parameter’. [2]
e) Velocity Zones
Once a set of samples are recorded or recalled from a disk, each sample can be split using a system called mapping. The sound which is mapped can mapped into a specific zone or range of notes or into velocity layers which allows the system to be programmed so that various key pressures will trigger two or more samples – pressing the key lightly would reproduce a softy recorded sample, while pressing the key harder would produce a more progressive sample. [1]
f) ADSR Curves
The envelope of an acoustical signal is composed of sections namely ADSR which work in combination with the timbre of the instrument all of which determine the subjective sound. ADSR abbreviates for Attack, Decay, Sustain and Release. These are the four parameters found on a basic synthesizer envelope generator and can be graphically represented in the form of an ADSR curve. An envelope generator is sometimes called a transient generator and is traditionally used to control the loudness envelope of sounds, though some modern designs allow for far greater flexibility. The Attack, Decay, and Release parameters are rate or time controls. Sustain is a level control. When a key is pressed, the envelope generator will begin to rise to its full level at the rate set by the attack parameter, upon reaching peak level it will begin to fall at the rate set by the decay parameter to the level set by the sustain control. The envelope will remain at the sustain level as long as the key is held down. Whenever a key is released, it will return to zero at the rate set by the release parameter. By adjusting the parameters of the ADSR on the envelope generator, what you are in fact doing is re-structuring the ADSR curves themselves and therefore manipulating its original structure influencing the sound of the instrument. [1][2]
3. Explain the following terms with reference to a synthesiser:
a) Multitimbral
A synthesizer is multitimbral if it is capable of producing more than one type of sound or timbre at a time. Usually this is described as the number of "parts" a unit can play 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. It is to be noted that multitimbral is distinct from the amount of polyphony- the number of actual notes the unit can simultaneously generate. [2]
b) Polyphony
Polyphony refers to the number of actual notes that the unit can simultaneously generate. All instruments have a finite number of notes they can produce at one time. A synthesizer might be 32-note polyphonic, and so on. The more notes of polyphony an instrument can produce, the more capable it is of playing complex arrangements and chords. If the polyphony of the instrument is exceeded, it must "steal" the notes it needs from others that are already sounding. For example, a synthesizer might steal the last note requested from the first one hit; the first note stops, and the new one begins to sound. Some synths and samplers use sophisticated algorithms for voice stealing, others allow you to pre-allocate a given number of voices to a particular MIDI channel, and so on. [2]
c) After touch
Aftertouch refers to MIDI data sent when pressure is applied to a keyboard after the key has been struck, and while it is being held down or sustained. Aftertouch is often routed to control vibrato, volume, and other parameters. There are two types: The most common is Channel Aftertouch (also known as Channel Pressure, Mono Aftertouch, and Mono Pressure) which looks at the keys being held, and transmits only the highest aftertouch value among them. Less common is Polyphonic Aftertouch, which allows each key being held to transmit a separate, independent aftertouch value. While polyphonic aftertouch can be extremely expressive, it can also be difficult for the unskilled to control, and can result in the transmission a great deal of unnecessary MIDI data, eating bandwidth and slowing MIDI response time. [2]
d) On velocity
In MIDI terms, velocity is how fast a key is moved by the player. There are actually two types: "Attack" velocity (normally referred to simply as "velocity") is how fast the key is struck, while release velocity refers to how fast the player lets go of the key at the end of a note. Velocity is often routed to control the volume of a note, how fast of an attack a note might have, or how bright a sound might be. Release velocity is commonly used to set the amount of time a note hangs or rings on after being released, whilst ‘on velocity’ refers to the attack/ execution of the note and the weight on which the key was pressed. [2]
4. Arrange the following devices in the order they would normally be used for subtractive analogue synthesis:
Subtractive Analog Synthesis refers to sound tailored with the use of filters to selectively remove certain harmonics from an initial waveform. That waveform may be a complex sound, like a sample, or a simple shape created by an oscillator. [2]
The order of devices for subtractive analog synthesis is as follows:
1. VCO- Abbreviation for Voltage Controlled Oscillator. It is an oscillator whose pitch (or frequency) is controlled by an input voltage.
2. VCF - Abbreviation for Voltage Controlled Filter. Similar to a VCA, except the control voltage affects a filter circuit.
3. VCA - Abbreviation for Voltage Controlled Amplifier. An electronic amplifier is a device for increasing the power of a signal. In synthesisers, the Voltage Controlled Amplifier [VCA] is currently used to create the volume envelope of sounds, the VCA being an amplification circuit whose gain is controlled by an external voltage source.
5. FM Synthesis:
a) What is an operator?
In FM synthesis, an operator is referred to as the software equivalent to common parts of other synthesizers such as an oscillator, envelope generator, envelope amplifier, etc. The FM process involves the use of at least two signal generators or operators to create and modify a voice. Often, this is done through the use of analog or digital generation of a signal that modulates or changes the tonal and amplitude characteristics of a carrier signal. The operators are combined in different ways to create different algorithms for producing fundamentally different types of sounds. [1][2]
b) What is a carrier?
A carrier is usually used in radio systems whereby the carrier is the transmitted electromagnetic wave, which is modulated to carry information. In Frequency Modulation synthesis –the same applies. The carrier in this context will be the audible signal whose frequency is altered by the modulator. [2]
c) What is a modulator?
A modulator applies to a control signal, which is being used to alter the perimeter of another signal. In synthesis, modulation is used to produce the various sonic variations that are associated with the synthesiser sound. [2]
d) What is an algorithm?
Algorithms can be thought of as a step-by-step problem-solving procedure, especially an established, recursive computational procedure for solving a problem in a finite number of steps. They are often run as subroutines to normal operations of computing devices. Algorithms are used in all sorts of signal processing devices to carry out specific aspects of their functionality. [2]
6. How does a digital oscillator produce a waveform?
An Oscillator is an electronic device that generates a periodic signal of a particular frequency, usually a sine wave, but other waveforms (square, sawtooth, triangle) are often used. Early synthesizers used oscillators as the basic component for all of the sounds of the machine. All of the filters and envelopes modified the sound created by the oscillator to produce the desired sound. This sound is created via ‘striking’ a note on the synthesiser or by playing back samples recorded on chips or by more modern synthesis techniques such as Physical Modelling, Frequency Modulation and the other synthesis types. [2]
7. How would a computer soundcard with onboard sounds usually generate its sounds?
Via the use of Wavetable Synthesis or Frequency Modulation Synthesis, a computer soundcard would usually generate its sounds. [2]
8. Which types of synthesiser are most suited to which applications?
Analogue - 1960’s Sci-Fi film soundtrack
FM -1980s synth pop music
Sample + Synth - Versatile ‘workstation’ keyboard
Wavetable - Emulation of acoustic instruments
Physical modelling - Tinkly electric piano sounds
========================================
Reference:
[1]Modern Recording Techniques D. M. Huber, R. Runstein
[2] www.sweetwater.com |
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Sat Apr 02, 2005 1:05 am |
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chemira
Joined: 03 Jan 2005
Posts: 50
Location: Nova Scotia Canada Eh! |
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Week 4
Music and Technology questions for Synthesis 1;
Describe each of the following methods of synthesis, and name one famous example/model of each:
a) Analogue
Analogue synthesis utilizes voltage controlled oscillators (VCO) a voltage controlled filter (VCF) and a voltage controlled amplifier VCA to shape the sound. By combining saw-tooth, square, sine, triangular waves and noise different sounds can be produced. Filters can be applied to any and all of the oscillators to shape the individual VCO’s or the whole sound. VCA’s can allow volume changes to the sound which may change to sounds attack or decay characteristics. The Minimoog is an example of an analogue synthesizer [1]
b) FM Synthesis
FM Synthesis or Frequency Modulator Synthesis utilizes one signal the modulator to affect another wave known as the carrier. FM synthesis involves the combination of two sounds to make a third sound that is different from the first two. Quote “FM SYNTHESIS - A method of creating music using frequencies to represent instruments” Unquote [4] The DX7 Synthesizer utilizes FM synthesis to make its sounds. [2] [3]
c) Physical Modelling
Physical Modelling is the Quote “creating and controlling a process that produces that sound.” Unquote.[5] By analyzing the content of what a sound is made up of the an instruments attack, tones and textures may be mimicked. [5] an Example of a Keyboard that uses physical modelling is a Generalmusic's Promega3.
d) Wavetable & S+S.
Wavetable and Sampling Synthesis is utilization of a stored sample of a complex moment of a real instrument. The PPG PRK is an example of a Wavetable Keyboard. [6] Sound blaster live value utilizes wave tables to create the sounds that are required in games.
Define the following terms within the synthesis discipline;
a) Oscillators
An Oscillator can be defined as a wave consisting of a frequency and amplitude. [7]
b) Filters
A filter can modify a sound by reducing spectral content which can share the tone of a sound. Filters can be defines by the process they perform or the range that they can effect. [8]
c) Envelopes and Amplifiers
An envelope will create a volume event that can change the actual attack and decay of a sound. The volume event may be adjusted to create sounds and textures that are not part of the original sound. [8]
d) LFOs
A low frequency Oscillator will modify attributes of a sound like volume or pitch to produce vibrato or tremolo. This is done using lower frequencies and speeds. [8]
e) Velocity Zones
Velocity zones are set out on a keyboard so that the speed and pressure that is applied to a key can translate into a closer representation of the interaction between the players style and the output sound. These zones can be progressive and uniform in amplitude or the key pressure can trigger another instrument at a preset value. [8] [9]
f) ADSR Curves
There are four sections of every sound envelope and they are attack, decay, sustain and release. These being the short form acronym ADSR.[9]
Explain the following terms with reference to a synthesizer:
a) multitimbral
A multi timbral synthesizer is capable of producing two or more instrument sounds at the same time.[10]
b) polyphony
keyboard that is capable of playing/triggering more than one key is said to be a polyphonic keyboard. The versatility of a keyboard with polyphony is limited to the maximum number of keys that can be played at the same time. [10]
c) after touch
After toucjh is the ability for a keyboards keys to sensing the amount of pressure that is applied to the keys. [10]
d) on velocity
Keyboard note on velocity is the value related to how hard the key was pressed that is transmitted as a MIDI message that will determine the relative volume that the note will sound. [10]
Arrange the following devices in the order they would normally be used for subtractive analogue synthesis:
a) VCO
b) VCA
c) VCF
For subtractive or analogue synthesis the first device would be the VCO or voltage controlled oscillator, then the VCF also know as the voltage controlled filter then finally the VCA or Voltage controlled amplifier. [11]
FM Synthesis
a) What is an operator?
An operator is an oscillator (VCO) and its associated filters generators, envelopes (VCF’s) and VCA’s. Operators can be combines to create very complex sounds. [12]
b) What is a carrier?
The Carrier is the final oscillator wave frequency which is the initial VCO in an operator. [12]
c) What is a modulator?
A modulator is an operator that can affect the Carrier by changing its pitch. The Modulator can also create harmonics. [13]
d) What is an algorithm?
An algorithm is a preset combination of operators that can be used in a repeated manner, usually accessed through a preset. [13]
How does a digital oscillator produce a waveform?
A digital oscillator can utilize normal VCO oscillator but it’s fundamentally controlled by a digital source for it’s parameters. This will create a more stable and flexible waveform. [15] 
How would a computer soundcard with onboard sounds usually generate its sounds?
Older sound cards used FM synthesis, newer cards utilize wave tables and some newer ones utilize FM and Wavetable synthesis. [14]
Which types of synthesizers are most suited to which applications?
Being a guitar player that Bleeds easily at the sight of MIDI cables, here goes……
Synths Applications Reasoning
Analogue ------------1980s synth pop music --------------------Big fat oscillators=big hair
FM -------------------1960’s Sci-Fi film soundtrack --------------Thin non descript sounds
Sample + Synth ----Versatile ‘workstation’ keyboard------------Choices choices
Wavetable -----------Tinkly electric piano sounds----------------not enough true character
Physical modeling--- Emulation of acoustic instruments---------recorded real deal
[1] http://www.geocities.com/SunsetStrip/Birdland/3547/analog.htm
[2] http://www.computermusic.co.uk/tutorial/fm/fm1.asp
[3] http://www.fm-alive.com/fm_explained.htm
[4] http://www.cheap56k.com/glossary/FM+synthesis.html
[5] http://www.harmony-central.com/Synth/Articles/Physical_Modeling/
[6] http://www.computeruser.com/resources/dictionary/definition.html?lookup=5694
[7] http://www-camil.music.uiuc.edu/classes/320A/lectures/01/Audio/synthesis.html
[8] http://www.sonicspot.com/guide/synthesis.html
[9] http://classes.berklee.edu/ms/classsupport/glossary.htm
[10] http://www.harmony-central.com/MIDI/Doc/tutorial.html
[11] http://www.geocities.com/SunsetStrip/Underground/2288/2ansynth.htm#Basic
[12] http://www.soundonsound.com/sos/may00/articles/synth.htm
[13] http://www.geocities.com/SunsetStrip/Underground/2288/2fmsynth.htm#M&C
[14] http://www.pcmech.com/show/multimedia/160/
[15] http://www.sequencer.de/synthesizer-basics.html |
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Sat Apr 02, 2005 5:11 pm |
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thx1138
Joined: 07 Jan 2005
Posts: 21
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Alex/Acousticalweaponsdivision, damn got to get a shorter yahoo profile 
Week 4 - Synthesis 1;
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:
The basic concept of analogue synthesis is known as 'subtractive' synthesis. It is the act of manipulating tone colour by filtering complex waveforms. It basically takes audio signals produced by oscillators and manipulates them by subtracting frequencies from the signals thus reshaping them.
A typical analogue synth consists of a keyboard, a low frequency oscillator (LFO), usually 2 envelope generators (EG), a filter and a voltage controlled amplifier (VCA). Almost all analogue synths have at least one voltage controlled filter (VCF), these are most often Low Pass Filters.
A low pass filter does exactly what it says - it filters low frequencies. Set at full it lets all low frequencies pass and at its lowest setting no low frequencies at all are allowed to pass.
A famous example of an analogue synthesiser is the MK. 1 MiniMoog as used by Rick Wakeman when he was in Yes in the 70's.
(www.geocities.com/sunsetstrip/studio/5821/analogue.html)
FM Synthesis:
Frequency modulation synthesis was introduced by John Chowning of Stanford university around 1973. It is where one oscillator is used to modulate or change the pitch of another. The oscillators or operators are known as the Modulator and the Carrier. The pitch of the carrier is changed/modulated in sync by the modulator.
It could be thought of in terms of one person singing and another grabbing that person's throat and shaking him/her rhythmically. The singer being the Carrier and the strangler being the modulator.
A Yamaha DX is an example of a FM Synthesiser.
(www.geocities.com/sunsetstrip/underground/2288/2fmsynth.htm#FM)
Physical Modelling:
Physical modelling synthesis is a method of creating audio with a numerical model of a physical system . It attempts to embody the characteristics of a real instrument using a model motivated by a physical analysis of a system.
A Yamaha VL1 is an example of a physical modelling synth.
(www.cs.caltech.edu/~ashman/ee107b/project107b.html)
Wavetable Synthesis and S + S:
This is a technique for generating sounds from digital signals. It stores digital samples of a sound from various instruments that can then be combined, edited and enhanced to produce sound defined by a digital signal. It reproduces the sound of musical instruments much better than FM synthesis does.
A Waldorf synth is an example of a Wavetable synthesiser.
Define the following terms within the synthesis discipline;
a) Oscillators
b) Filters
c) Envelopes and Amplifiers
d) LFOs
e) Velocity Zones
f) ADSR Curves
Oscillators:
This is a generic term describing the part of a synthesiser that produces the basic tone or sample of a synth patch.
Filters:
A filter is a device that blocks certain frequencies while letting other frequencies though.
Envelopes and Amplifiers:
An envelope is a signal processing device in a synthesiser that controls amplitude (volume) over a period of time. It give the sound its shape. It tells the synthesiser when volume should go up and down and the time takes to do so.
LFOs:
This stands for low frequency oscillator. They are generally used for adding vibrato or tremolo or otherwise controlling an audio signal. Low frequency implies frequencies below the audio range (20 Hz to 20 kHz), frequencies low enough so they aren't heard as a tone. It runs continuously at a low speed though many synthesisers have a re-trigger option allowing the LFO to be reset for each note played. It is a wave that repeats at a slow rate and has many different shapes and each one defines a different frequency of a waveform.
Velocity Zones:
Velocity is a measurement of how fast a key on the synthesiser descends and a measurement of how loud a note will be in relation to others. This is used to re-create the response of a real instrument as not every note is played at a uniform strength. Attack velocity (which is mostly just called velocity) is how fast the key is struck and release velocity is how fast the player lets go of the note.
ADSR curves:
These are types of amplitude envelope, the basic envelope of a synthesiser. Each letter stands for a different basic parameter of the envelope:
A - Attack - A control that defines the time it takes a note to get to its maximum attack level (the rise in amplitude when a note is triggered) or the speed at which a note reaches its maximum volume.
D - Decay - An envelope that determines the time it takes for the volume of a note to go from the attack level to the sustain level (the intermediate level between attack and sustain).
S - Sustain - The envelope that determines the level that a sound is played at while the note is held after the envelope portions attack and decay have been cycled though.
R - Release - The control envelope that determine how long it takes for the volume of a note to get from the sustain amplitude to 0 volume after a note is released.
(www.bimodular.crosswinds.net/glossary.htm)
Explain the following terms with reference to a synthesiser:
a) multitimbral
b) polyphony
c) after touch
d) on velocity
Multitimbral:
A synthesiser is multitimbral if it is capable of producing more than one type of sound or 'timbre' at a time. This is usually defined as the number of 'parts' a unit can play at a time.
If a synth is 16-part multitimbral it means it can produce 16 different sounds at once, a sound being defined as a single patch or pre-set on the synth.
Polyphony:
Polyphony is the ability to play more than one note simultaneously. The number of notes an instrument can play at a time.
A synthesiser said to be 32 note polyphonic could play 32 notes at a time. A 6 string guitar would be said to be 6 note polyphonic as it can only play up to 6 notes simultaneously.
After touch:
After touch is a synthesiser's response to when pressure is applied to a keyboard after the key has been struck and while it is being held down or sustained. It is often routed to control vibrato, volume and other parameters.
There are 2 types of after touch: Channel after touch, which looks at the keys/notes being held and uses only the highest after touch value. The other less common type is polyphonic after touch, which allows every note being held to have a separate, independent after touch value.
On Velocity:
On velocity is when the synth tracks how fast/hard a note on the keyboard was played.
(www.technical_t.com/Tgloss.html)
Arrange the following devices in the order they would normally be used for subtractive analogue synthesis:
a) VCO
b) VCA
c) VCF
VCO > VCA > VCF
Voltage Controlled Oscillator - where the pitch of a sound is controlled by voltage.
Voltage Controlled Amplifier - where the amplitude of a sound is controlled by a voltage.
Voltage Controlled Filter - where cut off frequency is controlled by a voltage.
Subtractive synthesis is a simple process:
Oscillator > Filter > Amplitude
An oscillator is used to generate a suitably bright sound, which is then routed through a filter.
A filter is used to cut off or cut down the brightness to something more suitable. This is routed through to an amplifier.
An amplifier is used to control the loudness of the sound over a period of time.
(www.geocities.com/underground/2288/2ansynth.htm#Basics)
FM Synthesis
a) What is an operator?
b) What is a carrier?
c) What is a modulator?
d) What is an algorithm?
Operators:
Operators are basically oscillators and an FM synth will typically have 4 or 6 operators. Operators are known as either the Carrier or the Modulator. At least 2 operators are required to make and modify a sound.
Carrier:
In FM synthesis a carrier is an operator that 'carries' the main audio output of a sound.
Modulator:
In FM synthesis the modulator is what is used to modify the output of another operator (the carrier) which is the process known as modulation.
Algorithm:
In FM synthesis an algorithm is a description of how the FM operators are set up and processed. They are the pre-set combinations of routing between operators that are available to you.
How does a digital oscillator produce a waveform?
A DCO (digitally controlled oscillator) creates a waveform in much the same way as a VCO creates one. Instead of electrical voltage as with a VCO, the waveforms are created by digital components. The DCO contains a sampled waveform stored as a series of numbers that is triggered at different frequencies.
How would a computer soundcard with onboard sounds usually generate its sounds?
A sound card usually generates its sounds in one of two ways, either FM synthesis in the case of most older and cheaper cards or by wave-table synthesis where sounds that can be triggered by MIDI signals are stored on the card itself.
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
1980's 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 - Wave-table |
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Sun Apr 03, 2005 9:47 am |
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ben m
Joined: 15 Sep 2002
Posts: 344
Location: UK |
| Synths -> Applications |
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One thing I'd like to pick everyone up on is the last question in the synthesis 1 set.
Everyone seems to have picked slightly different answers and there hasn't been a correct permutation yet.
There is a little ambiguity in the question but here is the 'model answer';
Analogue -> 1960’s Sci-Fi film soundtrack
FM -> Tinkly electric piano sounds
Sample + Synth -> 1980s synth pop music
Wavetable Versatile-> ‘workstation’ keyboard
Physical modelling -> Emulation of acoustic instruments
Could anyone explain the reasoning behind this answer?
cheers,
ben m |
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Sun Apr 03, 2005 10:55 am |
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hoaxwagon
Joined: 28 Feb 2005
Posts: 27
Location: Boulder Creek, CA USA |
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DD, hoaxwagon, MT wk 4 Q&A
Describe each of the following methods of synthesis, and name one famous example/model of each:
a) Analogue
subtractive synthesis, with a voltage control synthesiser like a modular Moog, envolves a voltage control
oscillator producing constant tone consisting of all frequencies, similar to noise. This noise is then run
through the filter to strip away frequencies and leave behind the side bands. These band can be
modulated by an envelope generator or an LFO. Some analogue synths have two oscilators that can
cross modulate to produce FM sounds like bells and percussion.
b) FM Synthesis
Frequency modulation synthesis was first implemented in the analogue domaine. It became the method
of synthesis used by Yamaha (DX7). Oscillators are called operators and carriers, depending on
whether they are being modulated or doing the modulating. An operator that is being modulated and is
at the end of a patch is the carrier. The method works by using multiple operators and preset algorithms
to achieve a more relistic sound.
c) Physical Modelling
Physical modelling uses mathematics to produce a waveform and store it on the memory. Avirtual
instrument is used to further simulate the reality of a person playing the actual instrument. This method
break the waveform into wave guide segments that all can be modulated seperately, making it possible
to fine tune the over all sound.
d) Wavetable & S+S
A sample sound is recorded and stored as a wavetable in a memorie chip in the oscillator. The two
oscillators are used for frequency modulation and are controlled with a keyboard.
Define the following terms within the synthesis discipline;
a) Oscillators
An oscillator generates waveforms with pitch related to the cycles per second of the tone.
b) Filters
Filters are the tone control of the oscillator generated waveforms. They take out certain frequencies to
further reviel a desired pitch.
c) Envelopes and Amplifiers
An envelope genrator is the modulator that provides the sound with attack, decay, sustain and release
qualities. The amplifier is the main volume of the mix of different carriers waveforms.
d) LFOs
A low frequency oscillator produces a sine wave voltage to the main oscillator. 1 to 10 htz. This is used
to create tremelo or vibratto effects.
e) Velocity Zones
Velocity zones are the increments of travel between 0 and 127 velocity.
f) ADSR Curves
ADSR curves are formed when a wave form is modulated by an envelope generator, providing attack,
decay, sustain and release.
Explain the following terms with reference to a synthesiser:
a) multitimbral
Multitimbral is a term used for a synthesiser that can play more than on patch at a time. For wxample, a
three note chord could consist of a piano, a bass and a string sound all playing together ( at the same
time)
b) polyphony
Polyphony is used to describe a synthesiser that can play more than one note at a time.
c) after touch
After touch is a controller that is activated by holding down a key and pressing it into the key bed. The
after touch can be routed seperately from the velocity so that when applied the tone could have effects
on it. The after touch can also be controlled by a foot pedel.
d) on velocity
On velocity would suggest that there are some form of dynamics allowed by the player. The lower the
velocity setting the least amount of dynamic control possible.
Arrange the following devices in the order they would normally be used for subtractive analogue
synthesis:
a) VCO VCO>VCF>VCA
b) VCA
c) VCF
FM Synthesis
a) What is an operator?
An operator is the name given to an oscilator by the Yamaha FM sythesis methods.
b) What is a carrier?
A carrier is an operator that is being modulated by another operator and is at the end of an algorythm.
c) What is a modulator?
A modulator can be a filter, an envelope generator or an oscillator that modulates another operator or
carrier.
d) What is an algorithm?
An algorythm is a preset patch of one of the many possibilities of routings available for quick access and
results in a realistic representation of an intended sound.
How does a digital oscillator produce a waveform?
A sample player uses a DAC instead of an oscillator to make its sound. A DAC is a Digital to Analog
Converter. This converts digital values (representing some waveform) into the analog signals that feed an
audio speaker (so that we can hear the waveform).
A digital oscillator generates a waveform by means of numerical calculations represented by digital
information in a software application. The DAC turns it into an audible sound.
How would a computer soundcard with onboard sounds usually generate its sounds?
The sounds on a computer soundcard are generated with the help of the DAC, digital to analogue
converter.
Which types of synthesiser are most suited to which applications?
Synths Applications
Analogue -1960’s Sci-Fi film soundtrack
FM -1980s synth pop music
Sample + Synth -Versatile ‘workstation’ keyboard
Wavetable -Tinkly electric piano sounds
Physical modelling -Emulation of acoustic instruments
Applications
1980s synth pop music
Versatile ‘workstation’ keyboard
Emulation of acoustic instruments
1960’s Sci-Fi film soundtrack
Tinkly electric piano sounds |
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Sun Apr 03, 2005 11:04 am |
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