Quiz: How Well Do You Know Your Synthesis?

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Quiz: How Well Do You Know Your Synthesis?

Post by HideawayStudio » Sat Jun 20, 2009 12:11 am

OK Here are 15 questions to set the men from the boys....

1. What is actually meant by a 24dB / octave low pass filter?
2. Why is the resonance control sometimes marked Q on synths?
3. What is meant by a subtractive synthesizer?
4. Why is a sawtooth a more useful waveform than a sinewave in subtractive synthesis?
5. Why are the oscillator ranges often marked in feet on older synths eg. 16', 8' & 4'
6. Why does stack (unison) mode sound the way it does?
7. Why are VCOs often more desired than DCOs?
8. Why are CV interfaces not used to control pitch on polyphonic synths?
9. What is meant by divide down architecture?
10. What is meant by the term Paraphonic and give an example of such a synth
11. How is white noise generated on a vintage synth?
12. What actually is a Chorus effect ie. how is it generated?
13. What is meant by oscillator sync mode?
14. What is a ring modulator?
15. Why can't bells be synthesized on all analog synths?
Last edited by HideawayStudio on Sat Jun 20, 2009 1:44 am, edited 1 time in total.

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Re: Quiz: How Well Do You Know Your Synthesis?

Post by Yoozer » Sat Jun 20, 2009 12:33 am

1. It's the steepness of the filter slope.
2. Quality factor is another term
3. Start with a waveform containing lots of harmonics, chop the ones away you don't need
4. Because there's actually something to subtract.
5. Organ pipe lengths
6. Because you're triggering all oscillators at the same time.
7. Drift, nonlinearity, which causes pleasant detuning
8. Because you can't figure out whether you've got 1.5 + 1.5 or 2 + 1 if you play 2 notes; there's only a single voltage.
9. Start with a master clock signal, divide by two to get the frequency of an octave lower
10. Korg PS3100, it means that you get full polyphony but shared filter / amplifier stage.
11. Amplifying circuit noise.
12. Using a (BBD) delay line where delay time is modulated
13. The starting point of the waveform of one oscillator is re-set on the basis of another oscillator's frequency.
14. It multiplies the volume of one oscillator with that of another
15. Because bell sounds are inharmonic, and the basic waveforms don't contain those waveforms (though you can get close with cross mod).

No Google/Wiki used.
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Re: Quiz: How Well Do You Know Your Synthesis?

Post by AstroDan » Sat Jun 20, 2009 1:14 am

Nicely done. =D>
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Re: Quiz: How Well Do You Know Your Synthesis?

Post by OriginalJambo » Sat Jun 20, 2009 1:18 am

HideawayStudio wrote:1. What is actually meant by a 24dB / octave low pass filter?
Describes how steep the filter slope is. The level of the signal is attended by 24 dB more for every subsequent octave, starting at the cut off frequency.
2. Why is the resonance control sometimes marked Q on synths?
Q for quality, in this case the "bandwith". Many parametic equalisers also use this terminology.
3. What is meant by a subtractive synthesizer?
Harmonics present in the original signal are attenuated with filters in order to produce new sounds.
4. Why is a sawtooth a more useful waveform than a sinewave in subtractive synthesis?
A sine wave contains no harmonics, only a fundamental. There's nothing to subtract.
5. Why are the oscillator ranges often marked in feet on older synths eg. 16', 8' & 4'
This is terminology used for organ pipe lengths. Double the length and you double the frequency.
6. Why does stack mode sound the way it does?
I must admit, I didn't know what you meant by "stack mode" here.
7. Why are VCOs often more desired than DCOs?
Oscillator drift provides a non-cyclic beating which is generally considered more musical.
8. Why are CV interfaces not used to control pitch on polyphonic synths?
Technically it's possible - you just need as many CV/gate inputs as you have voices. The introduction of MIDI made CV/gate control of polyphonic synthesisers rather redundant.
9. What is meant by divide down architecture?
A master oscillator is divided, often using digital flip-flops, to provide many possible pitches from one oscillator. Mainly used for sub-oscillators or combo organs and string machines.
10. What is meant by the term Paraphonic and give an example of such a synth
Where the pitches of oscillators can be controlled independantly via a keyboard, but all share the same filter/amplifier. The KORG Mono/Poly is an example.
11. How is white noise generated on a vintage synth?
With a white noise generator? ;) Seriously, I didn't know this one.
12. What actually is a Chorus effect ie. how is it generated?
The signal is delayed by a time that is modulated cyclically and then combined with the original. The result is an effect similar to several violin players in unison, a 12-string guitar, double-tracked vocals etc.
13. What is meant by oscillator sync mode?
The slave oscillator is forced to restart when the master completes its cycle.
14. What is a ring modulator?
A circuit that modulates the amplitude of one signal (the carrier) with the amplitude of another (the modular). This process creates new partials at two frequencies - both the sum, and the difference, of the frequencies of the carrier and the modulator.
15. Why can't bells be synthesized on all analog synths?
Natural bells contain inharmonics, that is harmonics that are not multiples of the fundamental frequency. These can only be created through frequency or amplidute/ring modulation. Not all analogue synthesisers offer this.
Last edited by OriginalJambo on Sat Jun 20, 2009 1:54 am, edited 1 time in total.

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Re: Quiz: How Well Do You Know Your Synthesis?

Post by cornutt » Sat Jun 20, 2009 1:29 am

Good job, Yoozer! Let me add a few things:
Yoozer wrote:1. It's the steepness of the filter slope.
More specifically, the amplitude of the output decreases by that many decibals for each octave that you move away from the cutoff frequency. And by definition, the cutoff frequency is the point at which the amplitude is 3 dB below the average amplitude within the passband.
4. Because there's actually something to subtract.
To add a bit: The sine wave is the most basic waveform in Fourier analysis. A sine wave has no harmonics. So, for instance, running a pure sine wave through a filter won't change the character of the signal; all it will do is increase or decrease the amplitude. (Although it's very difficult for an analog VCO to produce an absolutely pure sine.)
5. Organ pipe lengths
IIRC, it's the length of the C pipe in that octave (assuming ordinary flue pipes)
10. Korg PS3100, it means that you get full polyphony but shared filter / amplifier stage.
Also the Poly-800. And pretty much any string synth from the '70s.
11. Amplifying circuit noise.
More specifically, it amplifies the thermal noise of an unbiased P-N junction in a diode or transistor.
12. Using a (BBD) delay line where delay time is modulated
Various types of delay effects fall into a time spectrum. Basic chorusing is in the 8 to 20 millisecond neighborhood.
14. It multiplies the volume of one oscillator with that of another
I prefer to say that it multiplies the amplitudes; "volume" is a bit confusing in this context.
15. Because bell sounds are inharmonic, and the basic waveforms don't contain those waveforms (though you can get close with cross mod).
Right; by "inharmonic", we mean that the sounds contain overtones whose frequencies are not integer multiples of the fundemental frequency. Bells do that because they are three-dimensional objects, and can develop vibratory modes across all three axes.
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Re: Quiz: How Well Do You Know Your Synthesis?

Post by HideawayStudio » Sat Jun 20, 2009 1:37 am

cornutt wrote:
Right; by "inharmonic", we mean that the sounds contain overtones whose frequencies are not integer multiples of the fundemental frequency. Bells do that because they are three-dimensional objects, and can develop vibratory modes across all three axes.
A seriously good answer! =D>

Generally very good answers - there is still some detail to come for some of the other questions IMO :)

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Re: Quiz: How Well Do You Know Your Synthesis?

Post by Synthaholic » Sat Jun 20, 2009 1:41 am

Ok, I'm going to try to answer these without peeking at others' answers...
1. What is actually meant by a 24dB / octave low pass filter?
It refers to the slope, how much the filter attenuates the signal above the cutoff point.
2. Why is the resonance control sometimes marked Q on synths?
It refers to "quality" factor, how much damping takes place. Higher Q = more tendency to oscillate = resonance.
3. What is meant by a subtractive synthesizer?
It starts with a harmonically rich waveform and filters are used to remove the unwanted parts.
4. Why is a sawtooth a more useful waveform than a sinewave in subtractive synthesis?
Sawtooths are rich in harmonics, sinewaves have no harmonics so there's nothing to "subtract"--the filter has no effect on a sinewave except to reduce its amplitude.
5. Why are the oscillator ranges often marked in feet on older synths eg. 16', 8' & 4'
Octaves on pipe organs are defined by the lengths of the pipes.
6. Why does stack mode sound the way it does?
(Unison mode?) All the oscillators are sounding the same pitch at the same time, and with tuning drift it causes interesting effects.
7. Why are VCOs often more desired than DCOs?
VCOs drift in pitch, causing them to produce a more interesting sound when the frequencies interact.
8. Why are CV interfaces not used to control pitch on polyphonic synths?
You'd need a separate CV input for each voice of polyphony.
9. What is meant by divide down architecture?
The oscillators generate a single octave (the highest), and dividers are used to generate the lower octaves.
10. What is meant by the term Paraphonic and give an example of such a synth
Multiple oscillators that can play separate notes are fed into a single filter and/or VCA. Example = Korg Mono/Poly.
11. How is white noise generated on a vintage synth?
Either by amplifying a reverse-biased diode or transistor junction or with a shift-register based noise generator IC.
12. What actually is a Chorus effect ie. how is it generated?
The signal is run through a delay whose rate is modulated with an LFO, and is then mixed with the original signal to create the effect.
13. What is meant by oscillator sync mode?
When the master oscillator starts a new cycle, the slave (synced) oscillator is forced to restart its cycle.
14. What is a ring modulator?
It multiplies two input signals and produces an output containing the sum and difference of the input signals. Similar to amplitude modulation.
15. Why can't bells be synthesized on all analog synths?
Bells have complex harmonics that can't be derived using typical analog waveforms and a filter.
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Re: Quiz: How Well Do You Know Your Synthesis?

Post by HideawayStudio » Sat Jun 20, 2009 1:49 am

OK Some are putting too much emphasis on the lack of complex waveforms in answer to Q15 - the answer is more to do with the way the oscillators (and they can be basic sinewaves) are modulated....

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Re: Quiz: How Well Do You Know Your Synthesis?

Post by Automatic Gainsay » Sat Jun 20, 2009 1:54 am

Yoozer, SHAME ON YOU.

No wonder you have no PS-3100 love!

The PS-3100 is NOT PARAPHONIC. It and the rest of the PS series have dedicated filters and VCAs per note.
So, you got that one wrong. :wink:
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Re: Quiz: How Well Do You Know Your Synthesis?

Post by Zamise » Sat Jun 20, 2009 7:00 am

1. What is actually meant by a 24dB / octave low pass filter?
Means its more Moog like.
2. Why is the resonance control sometimes marked Q on synths?
=Qualizer
3. What is meant by a subtractive synthesizer?
If you turned everything up to max nothing would come out.
4. Why is a sawtooth a more useful waveform than a sinewave in subtractive synthesis?
because its less rounded
5. Why are the oscillator ranges often marked in feet on older synths eg. 16', 8' & 4'
because thats the distance to the same spot on the next wave
6. Why does stack (unison) mode sound the way it does?
because it plays both sides of a note at the same time
7. Why are VCOs often more desired than DCOs?
that is a random question
8. Why are CV interfaces not used to control pitch on polyphonic synths?
because they are not broad band
9. What is meant by divide down architecture?
Undocks part of the synth so you can play more notes that can sound difrent
10. What is meant by the term Paraphonic and give an example of such a synth
one big enough to stop your fall from an airplane to land safely on the ground, I can't think of any.
11. How is white noise generated on a vintage synth?
through a white noise generator duh
12. What actually is a Chorus effect ie. how is it generated?
similar to delay except it happens instantly with the pitch offset in small incraments, so not really anything like a delay really.
13. What is meant by oscillator sync mode?
keeps them from drifting apart unlike two canoes going over a waterfall
14. What is a ring modulator?
makes a sound more robotic sounding
15. Why can't bells be synthesized on all analog synths?
puss envelope retreats so it won't get defeated by a sharp crack
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Re: Quiz: How Well Do You Know Your Synthesis?

Post by HideawayStudio » Sat Jun 20, 2009 9:31 am

Zamise wrote:1. What is actually meant by a 24dB / octave low pass filter?
Means its more Moog like.
2. Why is the resonance control sometimes marked Q on synths?
=Qualizer
3. What is meant by a subtractive synthesizer?
If you turned everything up to max nothing would come out.
4. Why is a sawtooth a more useful waveform than a sinewave in subtractive synthesis?
because its less rounded
5. Why are the oscillator ranges often marked in feet on older synths eg. 16', 8' & 4'
because thats the distance to the same spot on the next wave
6. Why does stack (unison) mode sound the way it does?
because it plays both sides of a note at the same time
7. Why are VCOs often more desired than DCOs?
that is a random question
8. Why are CV interfaces not used to control pitch on polyphonic synths?
because they are not broad band
9. What is meant by divide down architecture?
Undocks part of the synth so you can play more notes that can sound difrent
10. What is meant by the term Paraphonic and give an example of such a synth
one big enough to stop your fall from an airplane to land safely on the ground, I can't think of any.
11. How is white noise generated on a vintage synth?
through a white noise generator duh
12. What actually is a Chorus effect ie. how is it generated?
similar to delay except it happens instantly with the pitch offset in small incraments, so not really anything like a delay really.
13. What is meant by oscillator sync mode?
keeps them from drifting apart unlike two canoes going over a waterfall
14. What is a ring modulator?
makes a sound more robotic sounding
15. Why can't bells be synthesized on all analog synths?
puss envelope retreats so it won't get defeated by a sharp crack
MAN WHAT ARE YOU ON!!?? :)

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Re: Quiz: How Well Do You Know Your Synthesis?

Post by adamstan » Sat Jun 20, 2009 9:37 am

This is terminology used for organ pipe lengths. Double the length and you double the frequency.
BZZZZZT! Wrong! Halve the length and you double the frequency. Frequency is inversely proportional to pipe's lenght. 16' is one octave LOWER than 8'.
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Re: Quiz: How Well Do You Know Your Synthesis?

Post by Big Gnome » Sat Jun 20, 2009 9:54 am

1. Frequencies above the cutoff are attenuated by 24dB per octave.
2. It stands for "quality".
3. A synthesizer which generates sound by removing components of harmonically rich tones.
4. An (ideal) sawtooth wave is comprised of every harmonic of the fundamental pitch at decreasing amplitudes, whereas a sine wave is a pure tone with no harmonics.
5. It is a holdover from pipe organs in which different octaves correspond to different pipe lengths.
6. Due to small pitch and phase discrepancies between the individual voices.
7. Partly because of their attractively drifty sound, but mostly due to rabid fetishizing on the internet. :wink:
8. Because CV can only be used to control individual voices.
9. An architecture wherein the pitches of twelve high-frequency master oscillators are "divided down" to produce lower octaves, thereby effectively providing polyphony without using a multitude of per-voice oscillators.
10. An architecture wherein a polyphonic oscillator section is processed by a single filter/VCA, e.g. the SCI Prelude a few feet to my right.
11. Beats me, although I've read it has something to do with overdriving transistors.
12. One or more delay lines are modulated by an LFO and mixed with the dry signal.
13. The phase of the slave oscillator is reset when the master oscillator's reaches zero.
14. It is a device that modulates the amplitude of one audio source by another, thereby producing sum and difference frequencies.
15. Many analog synths, especially prepatched ones, and especially those lacking ring modulation or FM, tend not to be well appointed for producing complex tones with many harmonically unrelated partials.
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Re: Quiz: How Well Do You Know Your Synthesis?

Post by Yoozer » Sat Jun 20, 2009 10:12 am

Automatic Gainsay wrote:The PS-3100 is NOT PARAPHONIC. It and the rest of the PS series have dedicated filters and VCAs per note.
So, you got that one wrong. :wink:
I know :(. I should've gone for the easy one.
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Re: Quiz: How Well Do You Know Your Synthesis?

Post by madtheory » Sat Jun 20, 2009 11:08 am

cornutt wrote:
Right; by "inharmonic", we mean that the sounds contain overtones whose frequencies are not integer multiples of the fundemental frequency. Bells do that because they are three-dimensional objects, and can develop vibratory modes across all three axes.
All vibrating bodies including strings and wood panels, are three dimensional. I don't know why bells produce harmonics that are equal or greater in level to the fundamental, but that's not the reason.

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