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Old 12th June 2012, 12:49 AM   #1
Jehan is offline Jehan  Indonesia
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Default odd order harmonic squelching?

is it possible to squelch the odd order harmonic while still retaining even order harmonic? For example, a square wave generator but with even order harmonic only, or a push pull but with odd order harmonic squelching, they will be ear-pleasing, right?
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Old 12th June 2012, 03:14 AM   #2
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No, no, and no, I'm afraid. Not in analogue anyway, unless you can isolate the section responsible for the odd harmonics and use feedback. A common strategy is to use an SS amp with lots of feedback, and then add a single-ended triode before or after.

Does a square wave have any even harmonics?

The most musical combination of harmonics depends on the music. A declining mix of 2H and 3H is arguably most desirable if some harmonics must be present.
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Old 12th June 2012, 03:24 AM   #3
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Yes, square waves may have even order harmonics. Duty cycle of square waves is equal to the number of even harmonics, from which above all even harmonics are absent.

You can not build such device that adds to any input signals even order only harmonics, but it is not needed. There are no desirable distortions in sound reproduction, it is a myth caused by misunderstanding. But there are desirable distortion in sound synthesis that is completely different application of electronics.

And there is less nasty behavior on overload that is represented by gradually bent transfer curve. When slightly overloaded it will give distortions of low order. The higher you overload it, the higher is order of distortions. It is about overload, of course!
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Last edited by Wavebourn; 12th June 2012 at 03:27 AM.
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Old 12th June 2012, 03:33 AM   #4
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One way to minimize any harmonics, and especially higher order harmonics is to limit the preceeding stage's harmonic amplitude as well as output stages. In otherwards keep the distortion level down before the output stage, as well as the output stage. As such, when 2nd and 3rd harmonics combine, 4th, 6th, and 9th orders etc will be minimized.

According to RCA Radiotron Designers Handbook, 26 engineers, 1960, the 7th harmonic is considered the first dissonant harmonic, then 9th order, "fundamental frequency is taken for convenience as 250hz".

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Old 12th June 2012, 04:13 AM   #5
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Quote:
Yes, square waves may have even order harmonics. Duty cycle of square waves is equal to the number of even harmonics, from which above all even harmonics are absent.
50% duty cycle is assumed unless otherwise stated.

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You can not build such device that adds to any input signals even order only harmonics,
SE triode can come close if deliberately arranged for that purpose.

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but it is not needed. There are no desirable distortions in sound reproduction,
Not quite the same point. "pleasing", "musical", and "desirable if some harmonics must be present" are all quite different from "desirable". They are especially different from "desirable distortions in sound reproduction" which is obviously a direct contradiction.

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it is a myth caused by misunderstanding.
Misunderstanding on the part of reproductionists. Fidelity cannot be reduced to reproduction.

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But there are desirable distortion in sound synthesis that is completely different application of electronics.
What is desirable or otherwise for synthesised sound is the same as for any other sound. Distortion is departure from the original. All sound sources contain harmonics, including synthesisers and traditional musical instruments. Why should it be OK to distort one, and not the other?
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Old 12th June 2012, 09:23 AM   #6
Jehan is offline Jehan  Indonesia
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sorry, my statement about "square waves generator but with even order harmonics only" is only an imagination, we already know that square waves generator is dominated by odd order harmonics, i post that way because i cant imagine such a waves generator that generates 2nd,4th,6th,and 8th harmonics, not 3rd,5th,7th,and 9th harmonics.
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Old 12th June 2012, 12:14 PM   #7
DF96 is offline DF96  England
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Originally Posted by PlasticIsGood
Misunderstanding on the part of reproductionists. Fidelity cannot be reduced to reproduction.
Hey, I have just discovered something new: I am a "reproductionist"! Is this the new name for what used to be called "hi-fi enthusiast" i.e. someone who wants to reproduce sound with as little change as reasonably possible? Does that mean that those who prefer changes should henceforth be known as distortionists?

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What is desirable or otherwise for synthesised sound is the same as for any other sound.
I think you misunderstand Wavebourn's point. In sound synthesis, 'distortion' is part of the instrument and presumably required to get a particular sound. In sound reproduction, distortion is generally unwanted unless it can be shown that it compensates for some other unavoidable distortion.
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Old 12th June 2012, 01:50 PM   #8
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Triangle waves are very rich in even harmonics.
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Old 12th June 2012, 01:56 PM   #9
12E1 is offline 12E1  United Kingdom
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Originally Posted by Jehan View Post
sorry, my statement about "square waves generator but with even order harmonics only" is only an imagination, we already know that square waves generator is dominated by odd order harmonics, i post that way because i cant imagine such a waves generator that generates 2nd,4th,6th,and 8th harmonics, not 3rd,5th,7th,and 9th harmonics.
A true square wave is made up from the fundamental and ONLY the odd harmonics. If there are any even harmonics then it's not a square wave.
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Old 12th June 2012, 02:01 PM   #10
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Originally Posted by 12E1 View Post
A true square wave is made up from the fundamental and ONLY the odd harmonics. If there are any even harmonics then it's not a square wave.
Not always. It depends on the DC level. If it is centered on 0V, then is true, but if not it has Cd term, so, even harmonics are present.
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