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What is worst - even or odd order of distortion
What is worst - even or odd order of distortion
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Old 30th January 2002, 12:33 PM   #1
DarkOne is offline DarkOne  Slovakia
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Default What is worst - even or odd order of distortion

I don't know which order of distorion is worst, because measuring of my amp shows that even order distortion is dominant.

Can someone help me with this dilema? I don't know, have I to work on my amp or is it OK?

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Old 30th January 2002, 12:50 PM   #2
AudioFreak is offline AudioFreak  Australia
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What is worst - even or odd order of distortion
2nd is the least offensive.... even order is usually less yuk than odd order.
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Old 30th January 2002, 01:16 PM   #3
ALW is offline ALW  United Kingdom
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Default Even / Odd

Even order distortion tends to fatten the sound, odd order sharpens it.

Odd order distortion in small quantities can make things sound faster / punchier and more dynamic - artificially of course.

Of more importance is the harmonic extension, low order harmonics are relatively unobtrusive, extended order is much more easily detected by the ear.

e.g. A well set up cartridge generates realtively high levels of 2nd / 3rd order harmonics. When a cartridge mistracks the absolute distortion level changes much less than one expects, but the distortion harmonics extend to the top of the audio band, where the ear is more sensitive.

It's why CD players used to sound so poor, they generated low levels of extended, non-musically-related distortion at low signal levels. It made them sound bright, sharp and nasty.
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Old 30th January 2002, 01:19 PM   #4
tvi is offline tvi  Australia
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You might find the following of interest:

<a href="http://hyperphysics.phy-astr.gsu.edu/hbase/music/pianof.html">The Piano</a>
"<i>Actually, the hammers are in sets for the keys which sound two or three strings. The striking point is about 1/7th of the way along the string to discriminate against the 7th harmonic resonance, which is significantly out of tune with the equal tempered scale. This "7th harmonic problem" can be illustrated by examining the musical intervals formed by a an exact <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/music/harmon.html#c1">harmonic sequence</a>.</i>"

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Old 30th January 2002, 01:38 PM   #5
DarkOne is offline DarkOne  Slovakia
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Thank You all, it is very usefull for me. So I can continue working on prototype.
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Old 1st February 2002, 01:45 AM   #6
seangoesbonk is offline seangoesbonk  Canada
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Default even/odd distortion

Quick Version:
Even order harmonic content is less offensive than odd order.

Longer (better) Version:

Harmonics are produced at multiples of the fundamental frequency.
Ex. If the frequency amplified(the fundamental) is 100Hz, then the 2nd harmonic is 200Hz, the 3rd is 300Hz, the 7th at 700Hz, etc...

Also, If the frequency is doubled, the same note in a musical scale is produced an octave higher.
Ex. The musical note "A" is produced at 440Hz, 880Hz, 1760Hz, 3520Hz, etc... (also at 220Hz, 110Hz, 55Hz, etc...)

By doing some simple math, you can see that the 2nd, 4th and 8th harmonics would sound "better" because they sound like the same notes 1, 2 and 3 octaves higher.

The other harmonics (3rd, 5th, 6th, 7th, 9th) would sound dissonant or "crappy-***"(as an engineer would put it) because they are related to the fundamental only in a mathematical sense, and not a musical one.

Tube amps produce mostly 2nd order harmonics. This accounts for the "fuller" (but less accurate) sound they produce.

But I don't want to spark a "tube vs SS" war...
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Old 1st February 2002, 02:18 AM   #7
Dave is offline Dave  New Zealand
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What is worst - even or odd order of distortion
As far as I understand amplifiers using large amounts of Global negative feedback tend to produce higher levels of the higher harmonics compared low feedback designs. Is this about right?
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Old 1st February 2002, 07:00 AM   #8
Chucko is offline Chucko
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Red face I don't think so Dave...

Check this op amp comparison (Japanese). It tests a number of common op amps in a non-inverting gain of 10 circuit, and provides the distortion results and FFTs of the residuals.

Note that the devices that get the best distortion measurements, and have the fewest high order harmonics, have very high amounts of global feedback - and are screamin' fast devices.

IMHO, global feedback is not by itself inherently good or bad; it's just another tool in the engineer's kit. Global feedback has the desirable property that it can clean up after several stages at once, rather like the catalytic converter on a car.

It's not a panacea, though; applying global feedback to a non-linear amplifier only makes it appear linear. Where global feedback really runs into problems is when the amplifier can't slew fast enough or doesn't have enough gain at all frequencies across the band, which results in what was once called TIM but should really be called slewing-induced distortion; or conversely when there is too much loop gain and phase delay, causing oscillation.

Global feedback earned a black eye from early SS power amps and op amps, which didn't have enough slew rate, gain bandwidth product, or open-loop linearity. These designs measured OK on simple test signals, but fell apart when you pushed them with real-world audio signals and loads. The result, in hindsight, was predictable, as was the backlash against global feedback that followed.

Note that most of the designs that use small amounts of global feedback are using comparatively large amounts of local feedback, in the form of emitter/cathode/source degeneration or inter-stage feedback loops.

At least that's the way it appears to me from 30 years or so of armchair audio engineering. I reserve the right to change my story in the face of hard evidence.
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Old 1st February 2002, 09:07 PM   #9
Nelson Pass is offline Nelson Pass  United States
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What is worst - even or odd order of distortion
Feedback is like a credit card. Used conservatively,
it's very helpful.
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Old 1st February 2002, 11:01 PM   #10
grataku is offline grataku  United States
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Just to be a little off topic, what about IMD where the frequencies have no harmonic relationship? That has to be nastier than harmonic distortion.
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