ben m
Joined: 15 Sep 2002
Posts: 344
Location: UK |
| Week 5 - Synthesis 2 |
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a) Which method of additive synthesis had widespread commercial success in the 1980s?
b) Describe the basic principles of this method of synthesis.
c) How this was implemented in the synthesisers that were commercially available.
What are the ADSR characteristics of the following instruments;
Piano
Guitar
Snare Drum
Violin
Describe the effect of the following modulations:
a) A VCO is going into a VCF and to a VCA. The VCO is being modulated by another VCO producing a square wave with a frequency of 15 Hz.
b) A VCO is going into a VCF and to a VCA. The VCF is being modulated by an ADSR.
c) A VCO is going into a VCF and to a VCA. The VCA is being modulated by another VCO producing a sine wave with a frequency of 10 Hz.
In early analogue subtractive synthesis, describe the difference between a voltage controlled oscillator and a conventional oscillator.
In subtractive synthesis, describe the function of the resonance control in a low-pass filter.
Describe three common ways an LFO might be used in analogue synthesis. Include references to other components of analogue synthesisers. Do not use abbreviations in your answer.
Give four terms used in FM (Frequency Modulation) synthesis and not in analogue synthesis.
Describe the waveform source in a wavetable synthesiser.
What technical problem would you expect to encounter when using an old analogue synthesizer for a lengthy live performance, even if the synthesizer is working to its original specifications?
What would be the effect of modulating the VCF of an analogue synthesizer with the LFO?
On the ADSR of an analogue synthesizer, how would you make a note decay to complete silence, no matter how long the key is pressed?
In an FM synthesizer, how would you quickly make a major (but probably random) change in the sound produced?
In an FM synthesizer, what would you adjust to change the high frequency content of a sound?
Which would you expect to sound best on an FM synthesizer: a tinkly electric piano sound or an imitation of string instruments?
Describe how frequency modulation can be achieved with a traditional analogue synthesizer, or modern equivalent. How will the end result differ compared to an FM synthesizer?
With reference to sounds creation, briefly explain the following;
a) Sample and Hold
b) Ring Modulator
With regard to FM synthesis, briefly explain the following;
a) Sidebands
b) Modulation Ratio
c) Modulation Index
With reference to physical modelling synthesis, briefly explain;
a) driver
b) Resonator
c) Modifier
In an FM algorithim, what differences in sound would occur from running 2 operators in series rather than parallel. |
Mon Apr 04, 2005 9:03 am |
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hoaxwagon
Joined: 28 Feb 2005
Posts: 27
Location: Boulder Creek, CA USA |
Hey folks this is me just retrieving my post so I can spell check it, oooops |
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Fri Apr 08, 2005 10:00 pm |
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hoaxwagon
Joined: 28 Feb 2005
Posts: 27
Location: Boulder Creek, CA USA |
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hoaxwagon’s Week 5 MT Q&A
a) Which method of additive synthesis had widespread commercial success in the 1980s?
FM
b) Describe the basic principles of this method of synthesis.
FM synthesis uses many operators that can be routed to form many algorithms for easy access to
realistic sounding patches. Each operator or module produces a sinewave that the carriers send to the
mixer. This mix is sent to a Digital audio converter and then to the amplifier.
FM involves putting two "pure" sound waves together in such a way that what you hear is not the
original waves but the mix - or modulation. It's a way of mixing two sounds together to create a third.
c) How this was implemented in the synthesisers that were commercially available.
On the soundcard inside the sythesiser.The Yamaha DX series of synthesizers was the commercially
available form of FM synthesis.
What are the ADSR characteristics of the following instruments;
Piano
Fast attack (10 %), fast (20 %) short decay, long sustain (75 %), and a somewhat fast (40%) release
Guitar
Not as fast of an attack as the piano (20%), and a 40 % decay down to a 25 % short sustain and then a
fast release (20%).
Snare Drum fast attack, instant decay, no sustain or release
Violin slow attack, long sustain, slightly faster release, no decay
Describe the effect of the following modulations:
a) A VCO is going into a VCF and to a VCA. The VCO is being modulated by another VCO
producing a square wave with a frequency of 15 Hz.
when an oscillator is modulating another operator it is referred to as cross-modulation and can be used
to create clangorous bell sounds. An LFO routed to the VCO creates a change in pitch (vibrato)
b) A VCO is going into a VCF and to a VCA. The VCF is being modulated by an ADSR.
Using contour or envelope generators will add dynamics to the sound as well as alter the timbre.
c) A VCO is going into a VCF and to a VCA. The VCA is being modulated by another VCO
producing a sine wave with a frequency of 10 Hz.
Since the human ear can’t pick a tone out of a 10 hertz wave the result is a rhythmic sensation of the
volume repeatedly going up and then back down. Modulating the VCA will change the amplitude
producing a tremolo effect.
In early analogue subtractive synthesis, describe the difference between a voltage controlled
oscillator and a conventional oscillator.
The voltage controlled oscillator uses voltage to generate a complex wave form that is manipulated
further to reveal a desired timbre. A conventional oscillator is electronically dependent and produces
sinewaves that are already fixed in pitch.
In subtractive synthesis, describe the function of the resonance control in a low-pass filter.
its function is to emphasize overtones near the cut off frequency
Describe three common ways an LFO might be used in analogue synthesis. Include references
to other components of analogue synthesizers. Do not use abbreviations in your answer.
A nice effect can be archived by connecting the triangle or sine output of a low frequency oscillator to
the cutoff-control input of the voltage control filter. Now the timbre of the sound slowly changes over
time. A low frequency oscillator can modulate the voltage control filter as well. A low frequency
oscillator routed through the voltage control filter will alter the tone color of the sound (trill). Modulating
the voltage control amplifier with a low frequency oscillator will change the amplitude producing a
tremolo effect.
Give four terms used in FM (Frequency Modulation) synthesis and not in analogue synthesis.
Operator, carrier, algorithm, digital control oscillator
Describe the waveform source in a wavetable synthesizer.
The waveform is stored on a memory chip as numerical calculations that represent the sound of other
instruments and is can be just one note.
What technical problem would you expect to encounter when using an old analogue
synthesizer for a lengthy live performance, even if the synthesizer is working to its original
specifications?
As an analog synth warms up it becomes less pitch stable.
What would be the effect of modulating the VCF of an analogue synthesizer with the LFO?
The effect would be a sweeping sensation of the frequencies. In other words, the volume of certain
frequencies is raised and lowered maybe 10 times per second. This is like what a wah wah pedal does.
On the ADSR of an analogue synthesizer, how would you make a note decay to complete
silence, no matter how long the key is pressed?
By applying just attack and decay without sustain or release
In an FM synthesizer, how would you quickly make a major (but probably random) change in
the sound produced?
Choose another algorithm
In an FM synthesizer, what would you adjust to change the high frequency content of a sound?
Turning up the modulation index should make the higher overtones more present.
Which would you expect to sound best on an FM synthesizer: a tinkly electric piano sound or
an imitation of string instruments?
Imitation of string instruments
Describe how frequency modulation can be achieved with a traditional analogue synthesizer,
or modern equivalent. How will the end result differ compared to an FM synthesizer?
Frequency modulation with an analogue synthesizer is achieved when one oscillator modulates another
oscillator. The result is limited and more tedious to set up and is not frequency stable across the
keyboard. In FM synthesis the modulators and carriers are all set up for easy changing of the sound.
This method is also polyphonic.
With reference to sounds creation, briefly explain the following
Sample and hold
Is a module that has two inputs and one output. One of the inputs takes the sample and lets it through
when triggered by a signal at the other input.
Ring modulator
Standard amplitude modulation (modulating the volume of one oscillator with a other oscillator) gives
nice organ sounds. But the most interesting use of a ring-modulator is feeding external sound sources
through. For example, a low frequency oscillator and a human-voice combined in a ring-modulator.
With regards to FM synthesis, briefly explain the following
side bands
Additional frequencies which appear either above and/or below the carrier frequency in a signal which
has been amplitude or frequency modulated .
Modulation index
The modulation index effects the loudness of the sideband overtones. The higher the modulation index
the more audible the overtones are. In this way the modulation index acts similarly to a low pass filter in
an analogue synthesizer.
With reference to physical modelling synthesis, briefly explain Driver, Resonator, Modifier
In physical modeling there is an instrument used to control the sound.
2 components of the "instrument"are a Driver and a Resonator.
The driver emulates the sound vibrations, like the reed, lip mouthpiece or the bowing of a string.
The resonator simulates the resonator part of an instrument, like the flare of a trumpet or the body of a
violin.
In an FM algorithm, what differences in sound would occur from running 2 operators in series
rather than parallel.
If 2 operators are run in series , the sounds of each operator remain individual and are mixed for a final
result. The operators run parallel results in the operator having an effect on the carrier. Modulation
occurs. |
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Fri Apr 08, 2005 10:09 pm |
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rachelh
Joined: 16 Jan 2005
Posts: 35
Location: Trinidad WI |
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a) Which method of additive synthesis had widespread commercial success in the 1980s?
The method of additive synthesis that has widespread commercial success in the 1980s is Frequency Modulation [FM] Synthesis, which is associated with analogue synthesisers.
[1]
b) Describe the basic principles of this method of synthesis.
The basic principles of FM synthesis is as follows:
1. Using at lease two signal generators or operators to create and modify a voice.
2. It is based around using the frequency of one signal (the modulator) to change the frequency of another audible signal (the carrier).
3. The sounds generated being complex signal waveforms, generated of one or more sine wave signals by other sine waves [operators] - It is a form/ method of additive synthesis
4. FM synthesis allows for a wide variety of waveforms to be created.
5. FM synthesis can be achieved via the use of digital or analogue synthesisers.
[1][2]
c) How this was implemented in the synthesisers that were commercially available.
FM synthesis was implemented in the synthesisers that were commercially available by the following process of generating sounds out of complex signal waveforms, which were enerated of one or more sine wave signals by other sine waves [operators] 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 [a similar method of 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][2]
What are the ADSR characteristics of the following instruments;
Piano
Guitar
Snare Drum
Violin
The term ADSR that abbreviates for Attack, Decay, Sustain and Release, are the characteristics of the envelope of a waveform.
The Attack time determines the speed at which the sound reaches its maximum loudness.
The 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.
The ADSR characteristics of a Piano could be as follows:
Attack -fast
Decay -rapid
Sustain - instantaneous
Release – instantaneous
The ADSR characteristics of a Guitar could be as follows:
Attack -fast
Decay -rapid
Sustain –dependant on note type , usually slightly prolonged
Release – gradual descent
The ADSR characteristics of a Snare Drum could be as follows:
Attack -fast
Decay -short
Sustain –instantaneous
Release –fast and prolonged gradual descent
The ADSR characteristics of a Violin could be as follows:
Attack –fast
Decay –prolonged
Sustain - prolonged
Release -fast
Describe the effect of the following modulations:[1][2] [3]
a) A VCO is going into a VCF and to a VCA. The VCO is being modulated by another VCO producing a square wave with a frequency of 15 Hz.
The effect of the above-mentioned modulation is that the signal/ waveform will be filtered and then the signal will be amplified then it will be modulated resulting in a square wave of 15Hz will be produced.
b) A VCO is going into a VCF and to a VCA. The VCF is being modulated by an ADSR.
The effect of the above-mentioned modulation is that the envelope of the original signal will be amplified, then it will be modulated guided by the parameters if the VCF/ ADSR. Thus according to the ADSR settings, the envelope of the waveform will be altered.
c) A VCO is going into a VCF and to a VCA. The VCA is being modulated by another VCO producing a sine wave with a frequency of 10 Hz.
The effect of the above-mentioned modulation is that the Tremolo effect will result. Where the tremolo effect is a cylical variation of amplitude level of a sound over a course of time.
In early analogue subtractive synthesis, describe the difference between a voltage controlled oscillator and a conventional oscillator.
In early subtractive synthesis the pitch of the VCO [voltage controlled oscillator] was controlled by an input voltage. Nowadays, conventional oscillators are digital namely DCO’s {digitally controlled oscillators} both types serve the same purpose, the difference being that the DCO is under digital control whereas the VCO is under analogue control and DCO’s tend to be much more stable and less susceptible to environmental conditions - especially with regard to tuning - than their analogue counterparts, although some synthesis complain they are too sterile and perfect sounding. [2]
In subtractive synthesis, describe the function of the resonance control in a low-pass filter.
In subtractive synthesis, the function of the resonance control in a low-pass filter is that it boosts the frequencies at the cut-off point. The resonance frequency is the frequency at which resonance occurs, an increase in resonance is proportional to a decrease in the amount of signal that will be allowed to pass through the filter and vice versa. [2]
Describe three common ways an LFO might be used in analogue synthesis. Include references to other components of analogue synthesisers. Do not use abbreviations in your answer.
Three ways in which a Low Frequency Oscillator might be used in analogue synthesis giving reference to other components of analogue synthesisers are to create varying levels of tremolo [cyclical variation of amplitude level of a sound over a course of time], vibrato [A cyclical variation in the pitch of a sound over time]
Give four terms used in FM (Frequency Modulation) synthesis and not in analogue synthesis.
Four terms used in FM synthesis and are not used in analogue synthesis are as follows:
1. Algorithm
2. Operator
3. Carrier
4. Digitally Controlled Oscillator [DCO]
Describe the waveform source in a Wavetable synthesiser.
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]
What technical problem would you expect to encounter when using an old analogue synthesizer for a lengthy live performance, even if the synthesizer is working to its original specifications? [4]
The technical problem that I will expect to encounter when using an old analogue synthesiser for a lengthy live performance is distortion, as the onset of this is gradual when using an analogue synthesiser, due to the oscillator’s pitch changing over a period of time.
What would be the effect of modulating the VCF of an analogue synthesizer with the LFO?
The effect if modulating the VCF of an analogue synthesiser with the LFO is that the timbre of the signal will change, as the ADSR characteristics will be altered by the VCF and the higher dynamics and overtones will be eliminated with the LFO.
On the ADSR of an analogue synthesizer, how would you make a note decay to complete silence, no matter how long the key is pressed?
For a note to decay to complete silence via the ADSR of an analogue synthesiser the settings on the sustain and release will have to be set to zero ‘0’ as sustain and release are the two parameters that control the duration of a signal.
In an FM synthesizer, how would you quickly make a major (but probably random) change in the sound produced?
In an FM synthesiser, a major but probably random change in the sound produce can be made by adjusting the modulating frequency.
In an FM synthesizer, what would you adjust to change the high frequency content of a sound?
In a FM synthesiser the device that could be used to change the high frequency content of a sound is to increase the frequency of one or all of the operators.
Which would you expect to sound best on an FM synthesizer: a tinkly electric piano sound or an imitation of string instruments?
A tinkly electric piano sound will sound better on an FM synthesiser.
Describe how frequency modulation can be achieved with a traditional analogue synthesizer, or modern equivalent. How will the end result differ compared to an FM synthesizer?
With reference to sound creation, briefly explain the following;
a) Sample and Hold
The term sample and hold describes a function or circuit found in early synthesisers that enable the instantaneous value voltage of a waveform to be captured. This captured sample is then transmitted or held within the set parameters until another course of action is taken. This voltage can be used to control some other parameter in the synthesiser such as a filter, dependant on the usage, a sample and hold circuit can produce pretty random sounding fluctuations in one or more aspects of a sound. [2]
b) Ring Modulator
A Ring Modulator is an audio mixer that combines two audio signals, and outputs the sum and difference of their combination. The frequencies found in the original signals are not passed through to the output. An example of the output of a ring modulator is resultant in inputting two sine waves into the modulator, frequencies 1500 and the other 500, the resultant frequency that will be outputted by the modulator is one of 1000 Hz. The more complex the waveform, the more clangourous and metallic the sound produced such as robotic voices. [2]
With regard to FM synthesis, briefly explain the following:
a) Sidebands
With respect to FM synthesis, a side band or sidebands refer to the multiple frequencies that are found in the output signal. Sidebands are the result of one signal or waveform being modulated by one or more signals or waveforms. They are produced whenever a signal is frequency modulated (FM) or amplitude modulated (AM) by another signal sum and difference frequencies are produced that appear with the signal – these resultant sum and difference frequencies are the sidebands. Upper Sidebands (USB) are the result of adding the signals together, and Lower Sidebands (LSB), are the result of subtracting them. Sidebands are a big part of what gives FM synthesizers their unique sound. [2]
b) Modulation Ratio
With respect to FM synthesis the modulation ratio refers to parameter by which modulation is to be set. It is the intensity of the signal[s]/ operators that will be used to modify the tonal and amplitude characteristics of the base carrier signal.
c) Modulation Index
In FM synthesis the modulation index refers to the change / ratio in the carrier’s frequency sweep, it
is the amount by which the carrier deviates from its un- modulated frequency. The modulation index is directly related to the amplitude of the Modulator. For any given Modulator frequency, it is the Modulation Index (and, therefore, the amplitude of the Modulator) that determines the amplitude of each of the components in the spectrum of the output signal. The modulation index can be found by dividing the carrier frequency by the modulator frequency. [5]
With reference to physical modelling synthesis, briefly explain: [6]
Physical Modeling (PhM) takes a unique and complex, but more intuitive approach to synthesizing sounds. Synthesis is accomplished by simulating the physical properties of a real or fictitious musical instrument mathematically by defining exciters and resonators.
a) Driver
In Physical Modelling synthesis, a driver is an exciter that is used to trigger the synthesiser to start generating sounds.
b) Resonator
In Physical Modelling synthesis, a resonator is the mathematical representation of the simulation of the physical properties of a real or fictitious instrument. They work by stimulating the instruments response to the exciter [which trigger the synthesizer to start generating sounds, by defining how the physical elements of the instrument would vibrate] This type of sound generation can be extremely complex and require heavy computation, so many currently available physical modelling synths use short-cuts or watered-down methods which enable them to respond in real-time.
c) Modifier
In Physical Modelling Synthesis, the modifier is used to control the changes in timbre and level of the signal over a time period. The upper modifier is the VCA (voltage controller amplifier) and the lower the VCF (voltage controller filter)
In an FM algorithm, what differences in sound would occur from running 2 operators in series rather than parallel.
In FM algorithm, the result of running or routing two operators in series is that the outputs from each of the operators would be summed together and no modulation of the sound will take place whereas if two operators were run in parallel the first will operate on the second in the chain and modulation will occur. [7]
========================================
Reference:
[1] Modern Recording Techniques D. M. Huber, R. Runstein
[2] www.sweetwater.com
[3] http://www.soundonsound.com/sos/jul99/articles/synthsecrets.htm
[4] Studio Recording Engineer
[5] Sound on Sound Synth Secrets- 12: An Introduction To Frequency Modulation
[6] http://www.sonicspot.com/guide/synthesistypes.html#physicalmodeling
[7] http://www.soundonsound.com/sos/may00/articles/synth.htm |
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Sat Apr 09, 2005 8:42 pm |
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chemira
Joined: 03 Jan 2005
Posts: 50
Location: Nova Scotia Canada Eh! |
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Week 5 Music Technology Synthesis
a) Which method of additive synthesis had widespread commercial success in the 1980s?
FM Synthesis was the additive synthesis used widely in the 1980’s. [1]
b) Describe the basic principles of this method of synthesis.
The techniques is called summing where by adding two or more wave forms together will create a completely different wave form called an algorithm. By combining algorithms together the complexity of the sounds can be more diverse and varied. Sounds can be made from combining several simple algorithms together to create a very complex sound. [1] [2]
c) How this was implemented in the synthesizers that were commercially available.
The DX series of synthesizer is a fine example of the FM synthesizers that were commercially produced. They utilized six operators to produce each tone and other sound algorithms could be loaded in using the ROM/RAM cartridge slot. [3]
What are the ADSR characteristics of the following instruments;
Attack Delay Sustain Release
Piano - Fast Medium, Little Medium
Guitar - Fast Fast med slow to fast
Snare Drum - Fast Fast little Fast
Violin - slow Medium Long Fast
Describe the effect of the following modulations:
a) A VCO is going into a VCF and to a VCA.The VCO is being modulated by another VCO producing a square wave with a frequency of 15 Hz.
This combination could create a very pulsed sound due to the rise and fall of the first VCO by the second VCO. At 15 HZ it would be very low tone possibly felt more than heard. [5]
b) A VCO is going into a VCF and to a VCA. The VCF is being modulated by an ADSR.
This could cause a spectral shift of frequencies depending on the attack/delay that will change the frequency spectrum present as the sound is presented. [5]
c) A VCO is going into a VCF and to a VCA. The VCA is being modulated by another VCO producing a sine wave with a frequency of 10 Hz.
This will cause the volume to rise and fall at the rate of 10 cycles per second which could be heard as swells or tremolo. [5]
In early analogue subtractive synthesis, describe the difference between a voltage controlled oscillator and a conventional oscillator.
A conventional oscillator DCO does not use the voltage sensed through the wave form to apply a control function to the oscillator. This will allow the control to be more stable and repeatable over time. Since the voltage of input can vary dependant on power available, age of components or voltage demands within the keyboard the analogue controlled oscillators will not be as precisely controllable.[5]
In subtractive synthesis, describe the function of the resonance control in a low-pass filter.
The resonance control in a low pass filter will boost the frequency at the cut off position. When more resonance is introduced around the cut of position the frequencies can begin to oscillate or feedback to a positive effect. [5]
Describe three common ways an LFO might be used in analogue synthesis. Include references to other components of analogue synthesizers. Do not use abbreviations in your answer.
Three common ways that Low Frequency Oscillators can produce useful sounds is as follows; 1) Low Frequency Oscillators can control a Voltage controlled Amplifiers causing a rise and fall in the volume called Tremolo. 2) The Low Frequency Oscillators can control Voltage controlled Oscillators to raise or lower their pitch called Vibrato. 3) Lastly they can a change in timber by controlling the Voltage controlled filter to create a trill effect. Another combination of the LFO being used could be in assembling a doppler effect which changes pitch and timber slightly creating the effect of a distant approach arrival then departure of an object passing by, the old train effect.
Give four terms used in FM (Frequency Modulation) synthesis and not in analogue synthesis.
Operator, carrier, algorithm, digital control oscillator
Describe the waveform source in a wavetable synthesiser.
The source for a waveform in a wavetable synthesizer is an actual sound sample that is stored digitally in RAM/Rom for later playback. These sound samples may be combinations of smaller wave files that together fit the characteristics of the intended sound.[6]
What technical problem would you expect to encounter when using an old analogue synthesizer for a lengthy live performance, even if the synthesizer is working to its original specifications?
Over time and as the synthesizer warms up the voltage available to produce sounds and contol will be affected by the heat which will increase the resistance in some circuits more than others. This will make the synthesizer control differently and the pitch may have changed because of this.
What would be the effect of modulating the VCF of an analogue synthesizer with the LFO?
On the ADSR of an analogue synthesizer, how would you make a note decay to complete silence, no matter how long the key is pressed?
By setting full sustain and no release time the sound will stop after the key is released.
In an FM synthesizer, how would you quickly make a major (but probably random) change in the sound produced?
By changing the order of oscillators the sounds would be completely different since the carrier would become the modulator and vice versa.
In an FM synthesizer, what would you adjust to change the high frequency content of a sound?
By adding a VCO with a high pass filter on it into the signal chain it will bring more higher spectrum content into the sound.
Which would you expect to sound best on an FM synthesizer: a tinkly electric piano sound or an imitation of string instruments?
The tinkly electric piano sound would suit FM synthesis best since there is little true modeling content in the sound produced.
Describe how frequency modulation can be achieved with a traditional analogue synthesizer, or modern equivalent. How will the end result differ compared to an FM synthesizer?
The VCO can be modulated by a LFO. The LFO increases and decreases the amplitude of the wave that the VCO is being carried on at the rate of the LFO. This will increase and decrease the pitch. The LFO will continue it’s cycle at it’s given rate irregardless of the speed of note changes. This may seem unnatural.
With reference to sounds creation, briefly explain the following;
a) Sample and Hold
Is a way of sampling a input voltage and utilizing it a s a point of reference later on. By sampling the voltage present in and VCO, LFO VCF or VCA you can trigger these peramiters later with repeatability. [7]
b) Ring Modulator
A ring modulator is an amplitude modulator that is a combination of two sources that create an output of sum and difference frequencies. The input signals do not reach the output for this type of sound production.
**Added April 11th at 12:12 AM right after work
With regard to FM synthesis, briefly explain the following;
a) Sidebands
Side bands are frequencies higher than and lower to the carrier frequency that contain energy due to the modulation process. [8]
b) Modulation Ratio
Modulation Ratio also referred to as C:M is the relationship between the carrier frequency and the modulation frequency expressed as an integer ratio. [9]
c)Modulation Index
This is the ratio of frequency deviation to the frequency of the modulating signal which can determine the number and spacing of side frequencies.
With reference to physical modeling synthesis, briefly explain;
a) driver
A driver is the primary physical event which will produce the sound of an instrument as it is made naturally as in the Hammers striking the strings in a piano or the buzz of a trumpets mouthpiece.[10]
b) Resonator
The resonator is the part of the instrument that will impart harmonics on the instrument sound such as the lid or case of the piano or the bell of a trumpet. [10]
d) Modifier
The modifier takes the initial physical event (driver) and converts this into the recognizable sound that the instrument is know to make., This would be the soundboard of a piano or the tubing in a trumpet. [10]
[1] http://www.sonicspot.com/guide/synthesistypes.html
[2] http://www.sfu.ca/sca/Manuals/fm/FM_Tutorial.html
[3] http://hem.passagen.se/tkolb/art/synth/dx7_e.htm
[4] http://www.sequencer.de/synthesizer-basics.html
[5] http://groovit.disjunkt.com/analog/subs/2ansynth.htm
[6] http://www.harmony-central.com/Synth/Articles/Wavetable_101/Wavetable-101.pdf
[7] http://www.soundonsound.com/sos/aug00/articles/synthsec.htm
[8] http://www.its.bldrdoc.gov/fs-1037/dir-033/_4841.htm
[9] http://www.sfu.ca/~truax/fmtut.html
[10] http://www.soundonsound.com/sos/aug98/articles/synthschool.html
I am tired
Last edited by chemira on Sun Apr 10, 2005 11:15 pm; edited 1 time in total |
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Sun Apr 10, 2005 10:51 am |
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thx1138
Joined: 07 Jan 2005
Posts: 21
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a) Which method of additive synthesis had widespread commercial success in the 1980s?
FM synthesis is a method of additive synthesis that had widespread commercial use during the 80's.
b) Describe the basic principles of this method of synthesis.
The basic principles of additive synthesis is producing a waveform by mixing/adding together more than one waveform such as the recreating of real instrument sounds by 'adding' together a suitable selection of sine waves.
(Music Engineering by Richard Brice)
c) How this was implemented in the synthesisers that were commercially available.
In the 80's one of the most popular FM synths was Yamaha's DX-7 which used operators to generate sounds as opposed to VCOs, VCFs and VCAs with the subtractive analogue synths. The DX's were available as 6 and 4 operator synthesisers.
(web.quick.cz/a.tom.x/dxage.html)
What are the ADSR characteristics of the following instruments;
Piano
Guitar
Snare Drum
Violin
A Piano can show the ADSR envelope of: fast attack, slow decay, slow sustain and a fast release time though this can depend on how the instrument is played, depending on how long notes are held for and the use of the piano pedals.
A Guitar has the ADSR characteristics: fast attack, slow decay, medium sustain and fast release time though a lot depends on the way the guitar is played for instance, palm muted strings would have a faster release than non palm muted strings.
A snare drum would have instant attack, fast decay, virtually no sustain and very fast release.
A violin typically has a slower attack than a guitar or piano, depending on how the instrument is bowed, fast decay, slow/long sustain and fast release. It depends quite a lot on how the instrument is played, playing notes staccato would exhibit a must faster attack and release and a much shorter sustain than playing it legato.
Describe the effect of the following modulations:
a) A VCO is going into a VCF and to a VCA. The VCO is being modulated by another VCO producing a square wave with a frequency of 15 Hz.
The effect of this modulation is a sound repeating 15 times a second with a square wave shape. The VCO is made to switch rapidly between 2 frequencies.
b) A VCO is going into a VCF and to a VCA. The VCF is being modulated by an ADSR.
The effect of this modulation is a filter sweep according to the ADSR settings.
c) A VCO is going into a VCF and to a VCA. The VCA is being modulated by another VCO producing a sine wave with a frequency of 10 Hz.
The effect of this modulation is a sound repeating 10 times a second with a sine wave shape so it will result in a fast tremolo effect.
In early analogue subtractive synthesis, describe the difference between a voltage-controlled oscillator and a conventional oscillator.
A voltage controlled oscillator is variably controlled in real time by a voltage whereas a conventional oscillator's frequency of oscillation is defined by a fixed pre-set value which can be changed by selecting a different pre-set.
In subtractive synthesis, describe the function of the resonance control in a low-pass filter.
Resonance is a parameter available in a low pass filter where the frequencies at the cut off position are boosted a little or a lot depending on the amount of resonance. With a lot of resonance the frequencies are boosted a lot and the lower frequencies start to diminish.
(www.geoctites.com/sunsetstrip/underground/2288/2ansynth.htm)
Describe three common ways an LFO might be used in analogue synthesis. Include references to other components of analogue synthesisers. Do not use abbreviations in your answer.
1. The low frequency oscillator can be routed to control a voltage-controlled oscillator to create changes in pitch for a vibrato effect.
2. The low frequency oscillator can be routed to control a voltage-controlled filter, which would alter the tone colour of the sound, by controlling the cut off frequency in time with the low frequency oscillator.
3. The low frequency oscillator can be routed to control a voltage-controlled amplifier creating a tremolo effect by causing changes in amplitude in time with the low frequency oscillator.
Give four terms used in FM (Frequency Modulation) synthesis and not in analogue synthesis.
Four terms used in FM synthesis and not in analogue synthesis are: operator, carrier, modulator and algorithm.
Describe the waveform source in a wave-table synthesiser.
Wave-table synthesis uses samples of real instruments as its sound source and not modulators, carriers etc.. Most instrument samples would be stored in a 16 bit 44.1 kHz format for better quality. The sounds are then played back at different pitches in accordance with the required note but when a sound is played back too fast it can suffer from 'munchkinistation'. It can also suffer when played back to slow and low so some wave-tables would have multiple samples of each instrument at different notes/pitches to enable realistic playback over several octaves.
(www.pctechguide.com)
What technical problem would you expect to encounter when using an old analogue synthesiser for a lengthy live performance, even if the synthesiser is working to its original specifications?
Analogue synths work best at room temperature so tuning drift can occur with changes in temperature.
What would be the effect of modulating the VCF of an analogue synthesiser with the LFO?
The effect of this modulation would be a filter sweep alteration in tone colour in sync with the LFO.
On the ADSR of an analogue synthesiser, how would you make a note decay to complete silence, no matter how long the key is pressed?
A note can be made to decay to complete silence no matter how long a key is held for by reducing the sustain to zero.
In an FM synthesiser, how would you quickly make a major (but probably random) change in the sound produced?
You could quickly (but possibly randomly) change the sound produced by selecting another algorithm.
In an FM synthesiser, what would you adjust to change the high frequency content of a sound?
Adjusting the high frequency content of a sound can be achieved by altering the modulator frequency.
Which would you expect to sound best on an FM synthesiser: a tinkly electric piano sound or an imitation of string instruments?
A tinkly electric piano sound would sound better on an FM synthesiser than an imitation of a stringed instrument.
Describe how frequency modulation can be achieved with a traditional analogue synthesiser, or modern equivalent. How will the end result differ compared to an FM synthesiser?
Frequency modulation can be achieved on an analogue synthesiser by routing the LFO through another oscillator. The LFO produces sine and triangle waves in the sub-audio range that contour the shape of the waveform it is sitting underneath. This is totally different to the results you would get from an FM synthesiser as the FM modulating signal would be inside the audio range and the changes to the resulting waveform will be far more complex.
With reference to sounds creation, briefly explain the following;
a) Sample and Hold
b) Ring Modulator
Sample and hold allows for periodic 'capture' of a frequency of a waveform which is held until the next sample is taken.
Ring modulation is an effect performed by multiplying 2 audio signals. Two waveforms are combined and the output is the sum and the difference of the two. It is also known as amplitude modulation,. It produces a signal rich in overtones, suitable for producing bell-like and metallic sounds.
With regard to FM synthesis, briefly explain the following;
a) Sidebands
b) Modulation Ratio
c) Modulation Index
Side Band:
In FM synthesis, side bands are additional sine wave components not necessarily harmonically related to the frequency of the carrier or modulator. They are typically additional frequencies above and below the carrier frequency.
Modulation Ration:
This is the ratio between the carrier and the modulating frequency, which determines the frequencies of the side bands.
Modulation Index:
The modulation index governs the power/amplitude of the side bands. It is defined as the maximum change in the carrier frequency, the maximum frequency deviation due to the depth or amount of modulation.
Modulation Index = Maximum carrier frequency deviation / Modulation frequency
With reference to physical modelling synthesis, briefly explain;
a) driver
b) Resonator
c) Modifier
With reference to physical modelling the driver, in its simplest terms, can be thought of as what actually produces the sound in the first place. Examples: when the pick of finger strikes a guitar string, breath passing through the mouthpiece of a wind instrument, the bow being drawn across a violin string.
The modifier is basically the part of the instrument which takes the initial vibration and changes it into what is recognised as the sound of that instrument, such as the sound box and bridge on a guitar or violin.
(www.soundonsound.com/sos/aug98/articles/synthschool.html)
The resonator modifies the harmonic content of the sound. It is typically the sound box or body of an instrument.
(www.acoustics.salford.ac.uk/acoustics_world/id/soundsynthesis/soundsynthesis.html)
A little confused here, the resonator and modifier appear to be roughly the same thing?
In an FM algorithm, what differences in sound would occur from running 2 operators in series rather than parallel.
Running operators in series in a 'chained' configuration: operator '2' would modulate operator '1'. This would result in a far less complex sound than operators in parallel.
(emusician.com/news/emusic_square_one_.html)
not too certain about the answer I have here. |
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Sun Apr 10, 2005 10:54 am |
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JohnA
Joined: 20 Jan 2005
Posts: 28
Location: Mid Glamorgan, UK |
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Audio Course
AUMT03
Week 5
SYNTHESIZERS 2
JohnA (mixindown)
a) Which method of additive synthesis had widespread commercial success in the 1980s?
FM Synthesis.
b) Describe the basic principles of this method of synthesis.
FM Synthesis is a way of mixing two or more sounds together to create a third.
FM synthesis involves putting two "pure" sound waves together in such a way that what you hear, is not the original waves, but a mix - or MODULATION. The CARRIER is the original VCO and the MODULATOR is the VCO that modulates the carrier. One oscillator modulates another.
c) How this was implemented in the synthesisers that were commercially available.
In 1983, the DX7 came out and for the first time, made DIGITAL FM SYNTHESIS available at an affordable price. Older analogue synthesizers used electronic components to generate ready-made complex waveforms, which are then shaped using filters. In the DX7 (it being digital) the waveforms are just streams of numbers generated by the onboard computer to represent how the audio waveform should sound. All the mixing is done in the digital domain usind FM Synthesis.
What are the ADSR characteristics of the following instruments;
Piano: Fast attack, slow decay, slow release, fast decay.
Guitar: Fast attack, slow decay, medium release, fast decay.
Snare Very fast attack, fast decay, small amount of sustain, fast release.
Violin: Very slow attack, fast decay, slow sustain, fast release.
Describe the effect of the following modulations:
a) A VCO is going into a VCF and to a VCA. The VCO is being modulated by another VCO producing a square wave with a frequency of 15 Hz.
The VCO that is being modulated will produce siren like changes is pitch. This well be 15 times a second.
b) A VCO is going into a VCF and to a VCA. The VCF is being modulated by an ADSR.
The VCF frequencies will be controlled by the ADSR settings.
c) A VCO is going into a VCF and to a VCA. The VCA is being modulated by another VCO producing a sine wave with a frequency of 10 Hz.
This will produce a vibrato effect. If you feed this to a Modulation Wheel you can control the amount of the vibrato effect.
In early analogue subtractive synthesis, describe the difference between a voltage controlled oscillator and a conventional oscillator.
The difference between a VCO and a conventional oscillator is a Voltage Controlled Oscillator can change its frequency but a conventional oscillator has a fixed frequency and is not dependent on voltage.
In subtractive synthesis, describe the function of the resonance control in a low-pass filter.
The resonance control boosts the frequencies “around” the cut-off point. As you increase the resonance, the boosted band becomes narrower.
Describe three common ways an LFO might be used in analogue synthesis. Include references to other components of analogue synthesisers. Do not use abbreviations in your answer.
A Low Frequency Oscillator may be used to modulate a Voltage Controlled Oscillator that is producing a waveform.
It could also be routed to the filters of Envelope Generators to modulate the timbre or output level. You could send it through the Voltage Control Oscillator to alter the Pitch of the sound.
You could use a sinewave and assign a Low Frequency Oscillator to modulate the resonance at a high value. This will give a kink of siren sound. If you take the resonance setting down low, you will get a kind of throbbing effect on the sound.
Give four terms used in FM (Frequency Modulation) synthesis and not in analogue synthesis.
Four terms would include the Operator, Carrier, Modulator and Algorithm.
Describe the waveform source in a wavetable synthesiser.
In a Wavetable sinthesizer, the instrument is digitally sampled and the audio samples or waveforms are stored in an array known as a “wavetable” in the synthesizer. The wavetable is a table of stored sound waves that are digitized samples of actual recorded sound. This is usually stored in ROM (Read Only Memory) on a chip. To save memory in this system, most wavetables do not store a recording of every note of every instrument. Only a handful of notes are stored for each instrument.
What technical problem would you expect to encounter when using an old analogue synthesizer for a lengthy live performance, even if the synthesizer is working to its original specifications?
Until they have warmed up, the oscillators tend to drift a little. They can also be prone to overheating and their reliability can be effected by humidity.
What would be the effect of modulating the VCF of an analogue synthesizer with the LFO?
A LFO routed through the VCF will alter the tone colour of the sound (trill) and have a kind of filter sweeping effect.
On the ADSR of an analogue synthesizer, how would you make a note decay to complete silence, no matter how long the key is pressed?
Set no Sustain and no release.
In an FM synthesizer, how would you quickly make a major (but probably random) change in the sound produced?
You could record the knob settings in digital memory. These could be recalled by the push of a button. You could also change the frequency of the modulator.
In an FM synthesizer, what would you adjust to change the high frequency content of a sound?
You would adjust the frequency of the modulator in audio rate where the sidebands can be heard.
Which would you expect to sound best on an FM synthesizer: a tinkly electric piano sound or an imitation of string instruments?
A tinkly electric piano.
Describe how frequency modulation can be achieved with a traditional analogue synthesizer, or modern equivalent. How will the end result differ compared to an FM synthesizer?
Feed a LFO into the VCO. This way, the LFO can modulate the VCO. With an FM Synthesizer, you can use more than two VCO’s.
With reference to sounds creation, briefly explain the following;
a) Sample and Hold
Sample and Hold is a circuit that has two inputs and one output. It takes an analogue voltage and stores it on a capacitor for a short period of time. The part of the circuit that times the sample is called the Clock. This is like a “snapshot” of the inputted signal and should hold the voltage constant for as long as possible (a good capacitor is important here) until the A/D converter has "measured" the voltage. The signal could be an audio signal, an envelope or an LFO, or some other signal.
c) Ring Modulator
A ring modulator is a simple device that can be used to create unusual sounds from an instruments output. It effectively takes two signals (each with some frequency), and produces a signal containing the sum and differences of those frequencies. These frequencies will typically be non-harmonic, so the ring modulator can create some very dissonant sounds. For this reason, ring modulation is not a widely used effect.
A Ring Modulator is a circuit that produces a dense cluster of non-harmonic overtones. It is an effect by performed by multiplying two audio signals. These are combined and the sum and the differences of the two are outputted.
Ring Modulator performs a variation of amplitude modulation in which two input signals are multiplied creating an output that contains the sum and difference of the input signals (called sidebands), but without the original input signals themselves. The result is a very strange clanging, bell-like sound that can only be created with a ring modulator. Useful for producing gong sounds, bell sounds, and many strange sounds having no description. Sometimes referred to as a 'Balanced Modulator'.
With regard to FM synthesis, briefly explain the following;
a) Sidebands
When the modulation is raised to the audio range, we hear new timbres composed of frequencies. These are called SIDEBANDS. These appear symmetrically around the carrier frequency. Those above the carrier frequency are called “upper sidebands” and below are called “lower sidebands”.
b) Modulation Ratio
This is a way of calculating sidebands (as defined above) but instead of dealing with them in Hz, we use ratio. The Modulation Ratio is referred to as the C:M Ratio, where C is the Carrier and M is the Modulator. So if C = 100 and M = 200, the C:M Ratio would be 1:2.
c) Modulation Index
The modulation index is the amplitude of the modulator. It affects the loudness of the sideband overtones so the higher the modulation index, the more prominent the overtones will be.
With reference to physical modelling synthesis, briefly explain;
a) Driver
The driver is what produces the sound in the first place. The driver in a guitar would be the plectrum or the fingers that are hitting the strings. This is the thing that is actually responsible for producing the sound. The driver for a violin is the bow, for flute it is the breath of the musician. With drums it would be the drum sticks.
b) Modifier
A modifier is the part of a musical instrument that takes the initial vibration and changes it into the sound of that instrument. On a guitar, this is the bridge and sound box. On a saxophone it is the tube of the body.
c) Resonator
The resonator is the part of the instrument that alters the harmonics of the sound. With an acoustic guitar, this is the body or sound box of the instrument.
In an FM algorithim, what differences in sound would occur from running 2 operators in series rather than parallel.
When two operators are run in series, they modify one another. The first operator plays, alters the second, and you hear that sound. In parallel, both operators play and you hear the sound of both at the same time.
http://www.samplecraze.com/tutorial.php?xTutorialID=5
http://en.wikipedia.org/wiki/Ring_modulator
http://www.soundslogical.com/support/wavewarp/documentation/english/documentparts/ADSR_Envelope.html
http://www.harmony-central.com/Synth/Data/Moog/MemoryMoog-01.html
http://www.soundonsound.com/sos/aug00/articles/synthsec.htm
http://www.phys.ualberta.ca/~gingrich/phys395/notes/node156.html
http://home.eol.ca/~quirke/synthesis/dx7.html
John A |
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Mon Apr 11, 2005 12:04 pm |
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