ben m
Joined: 15 Sep 2002
Posts: 337
Location: UK |
| Week 5 -Synthesizers 2 |
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Hi,
Firstly, I will post comments on lasts weeks answers later this afternoon.
More questions on synthesis this week for you all.
Again, in-depth answers are required to show an understanding of the topic rather than simple yes or no answers. Make sure that all your terminology is correct as this will be rewarded in the exam.
 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?
Any problems then please post them in this forum.
Good Luck.
ben m
_________________
ben@audiocourses.com |
Mon Sep 29, 2003 6:13 pm |
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mommi
Joined: 21 Apr 2003
Posts: 47
Location: Tallinn, Estonia |
| Where to start |
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I'm a bit clueless with at least the first three questions. Maybe I'm just getting tired, lot of info there on the net, but can't take the important part out from there.
Any hints please?
mommi |
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Thu Oct 02, 2003 6:16 pm |
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Albow
Joined: 02 Sep 2003
Posts: 27
Location: Spain |
Bloody Hell that's a good link. Got any more?
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Thu Oct 02, 2003 10:45 pm |
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julesf
Joined: 31 Aug 2003
Posts: 58
Location: Southampton, UK |
What on Albow m8 
Jules. |
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Thu Oct 02, 2003 11:24 pm |
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Albow
Joined: 02 Sep 2003
Posts: 27
Location: Spain |
Well, synths in general, but specifically for this week's questions. Struggling a bit TBH. |
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Fri Oct 03, 2003 12:15 am |
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mommi
Joined: 21 Apr 2003
Posts: 47
Location: Tallinn, Estonia |
Thanks Jules, the pdf is very compact and informative. What I don't catch at all are the first questions though. I principally understand the idea of additive synthesis, but seem not being able to differentiate between <i>types</i> of additive synthesis. For me it seems an additive synthesis is itself one type of synthesis. What are the <i>subtypes</i> and where to read about them?
mommi |
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Fri Oct 03, 2003 12:18 am |
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julesf
Joined: 31 Aug 2003
Posts: 58
Location: Southampton, UK |
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OK Guys,
The principle is really quite simple. Synthesis is the art of synthetically shaping or re-shaping a waveform. So you have to have a waveform to start with, say a sine wave audio oscillator.
Subtractive synthesis shapes the sound by removing harmonics from the waveform by using a filter, and maybe then modifying the dynamic curve with an envelope shaper controlling an amplifiers gain (VCA)
Additive synthesis takes more than one waveform and "adds" them together in some way to make a different waveform, again the dynamic curve can also be altered. So really a Hammond Organ could be said to be additive synthesis as the multiple waveforms produced by the electronics or tone wheels are being added together to make the final waveform. This is achieved by pulling out the drawbars and mixing or "adding" the various waveforms together. No dynamic shaping here though eh! 
It is now not difficult to see that an analogue synth could be seen as being additive and subtractive at the same time. You normally have two oscillators right, and a pink or white noise generator. You can mix the oscillators and noise generator, or get one oscillator to modulate the other (Sound familiar), or get the noise generator to modulate an oscillator. All of this is additive synthesis. However if you then pass the waveform that results from your electronic sorcery into the VCF and modulate that with the control voltage from the envelope generator, which then sweeps the filter removing some harmonic content, then this is the subtractive part of the synthesis.
Hope that has helped and not hindered.
Check this link for a more professional explanation of additive synthesis.
http://www.soundonsound.com/sos/jun00/articles/synthsec.htm
Cheers,
Jules 
Last edited by julesf on Fri Oct 03, 2003 5:12 am; edited 2 times in total |
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Fri Oct 03, 2003 1:13 am |
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julesf
Joined: 31 Aug 2003
Posts: 58
Location: Southampton, UK |
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MT Week 5 Synthesis
<b>a) Which method of additive synthesis had widespread commercial success in the 1980s? </b>
FM synthesis
<b>b) Describe the basic principles of this method of synthesis. </b>
The system uses digital sine wave operators. One operator is assigned as the carrier which is the output waveform operator and is placed last in the array. The other operators normally act as modulators and shape the sound of the carrier by frequency modulation. Digital algorithms allow the operators to perform according to a pre programmed configuration, a number of factory assigned algorithms are included within the parameters of the instrument.
<b>c) How was this implemented in the synthesisers that were commercially available. </b>
Yamaha dominated the FM scene in the 80's with the DX7 and the DX11, a cut down later version. The DX7 offered six on board operator's sixteen-note polyphony (massive for the 80's) as well as a filter and the usual envelope shapers. The DX11 used just four operators, had ADRS dynamic shaping, basic filters and only sported 8-note polyphony despite having multi timbre capability with zoning. The DX7 was the biggest selling all time FM synth, also made famous by heavy use on Steve Winwards "Arc Of A Diver" Album.
<b>What are the ADSR characteristics of the following instruments;
Piano
Guitar
Snare Drum
Violin </b>
Not sure how to present ADSR characteristics without drawing curves.
Piano can display: fast attack, slow decay, no sustain, fast release. (depends on playing and pedal use)
Guitar can display: fast attack, slow decay, no sustain, fast release (if damped)
Snare drum displays fast attack, fast decay, no sustain, no release.
Violin can display: fast attack, no decay, long sustain, and fast release. Depends on how the instrument is bowed.
<b>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>
The pitch of the VCO will rise sharply up and down at a rate of 15 times a second. The amount of pitch increase and decrease will depend upon the amount of modulation applied to the VCO control circuit.
<b>b) A VCO is going into a VCF and to a VCA. The VCF is being modulated by an ADSR. </b>
The sound will filter sweep in accordance with the settings of the ADSR. This is how the classic Moog scream is produced.
<b>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. </b>
This will provide a 10Hz tremolo effect.
<b>In early analogue subtractive synthesis, describe the difference between a voltage controlled oscillator and a conventional oscillator.</b>
A conventional oscillator is fixed frequency set by a preset, although the frequency can be altered by adjusting the preset. A voltage-controlled oscillator is real-time variable across its frequency range by acting
Upon the control voltage from other modifiers in the synth. This enables modification of the frequency to be made by any other module that outputs some form of control voltage.</b>
<b> In subtractive synthesis, describe the function of the resonance control in a low-pass filter.</b>
The resonance control allows frequencies at the cut off point to be boosted or cut. Boosting sub sonic frequency resonance can produce a truly room (and speaker cone) shattering result.
<b>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. </b>
The Low Frequency Oscillator may be set to sine wave and may be connected to the control voltage input of the Voltage Controlled Filter via the Modulation potentiometer. When the Modulation Potentiometer is raised it will send the output to the Voltage Controlled Filter and cause the frequency band pass to be altered. This will provide a way of putting expression in the sound and works best when added to sustained notes.
The Low frequency oscillator may be set to a low frequency square wave, and the output sent to the voltage-controlled amplifier. This will cause the voltage controlled amplifier to trigger in time with the low frequency oscillator which when used with the correct voltage controlled filter settings will produce the sound of a four on the floor kick drum.
The Low frequency oscillator may be set to a low frequency sine wave, and the output sent to the voltage-controlled amplifier via the modulation potentiometer. This will cause the voltage-controlled amplifier to modulate to the low frequency oscillator when the modulation control is raised producing a traditional tremolo effect.
<b> Give four terms used in FM (Frequency Modulation) synthesis and not in analogue synthesis. </b>
Operator, Carrier, Algorithm, Modulator.
<b>Describe the waveform source in a wavetable synthesiser. </b>
The source is from a wavetable of digital algorithms.
<b> What technical problem would you expect to encounter when using an old analogue synthesizer for a lengthy live performance, even if the synthesiser is working to its original specifications? </b>
Tuning drift due to temperature change.
<b>What would be the effect of modulating the VCF of an analogue synthesizer with the LFO? </b>
It would cause the filter to sweep in time with the LFO.
<b> On the ADSR of an analogue synthesizer, how would you make note decay to complete silence, no matter how long the key is pressed? </b>
Turn the sustain right down and just work the envelope generator as an AD generator.
<b> In an FM synthesizer, how would you quickly make a major (but probably random) change in the sound produced? </b>
Select a different operator algorithm.
<b> In an FM synthesizer, what would you adjust to change the high frequency content of a sound? </b>
Digital controlled filter.
<b> Which would you expect to sound best on an FM synthesizer: a tinkly electric piano sound or an imitation of string instruments? </b>
Tinkly electric piano sound
<b>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? </b>
Use one VCO as the carrier routed through the VCF and VCA. Use another VCO as the modulator and use the LFO to modulate the modulator VCO, i.e. emulate an algorithm. The end result will not be anything like an FM synth, for a start it might sound half-decent , but the waveforms will not be complex enough to produce interesting sounds. Also there would be only one carrier. An FM synth with one carrier and one modulator would also sound uninteresting, comes to think of it they don't sound that interesting with four
Last edited by julesf on Sat Oct 04, 2003 5:47 am; edited 2 times in total |
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Fri Oct 03, 2003 3:44 am |
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