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Old 21st December 2002, 02:54 PM   #1
Bricolo is offline Bricolo  France
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Default What is an harmonic?

I always read things about ..th harmonic distortion

but what is an harmonic?
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Old 21st December 2002, 03:08 PM   #2
eLarson is offline eLarson  United States
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Electronically speaking, you can think of them as integer multiples of the intended frequency caused
by a nonlinear gain device. (Or a not-quite-all-the-
way-linear gain device.)

Erik
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Old 21st December 2002, 04:10 PM   #3
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Old 21st December 2002, 04:17 PM   #4
dhaen is offline dhaen  Europe
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Harmonics occur naturally in musical sounds. They are what makes musical one musical note sound "rich" rather than "thin".
Each musical instrument has a harmonic signature that makes it recognisable to us.
When an amplifier distorts this harmonic pattern, it can either make the sound different - or, unpleasant.
We normally test with a single (sine wave) frequency, and check that no other frequencies are generated.
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Old 21st December 2002, 05:15 PM   #5
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Default One more try...

Eric Larson wasn't wrong in any respect, but let me try some more explanation:

Say you have a sound wave of some frequency. The favorite note for tuning instruments is an "A" of frequency 440 hz. Also called "A-440." The harmonics of that are frequencies that are integer multiples of that frequency, 2 x 440, 3 x 440, 4 x 440, etc.
giving 880 hz, 1320 hz, 1760 hz, etc. These would specifically be referred to as the second harmonic, third harmonic, fourth harmonic, etc. The original frequency is usually referred to as the "fundamental" although it is also the first harmonic.

If there is something about the system that is prone to oscillating at one of those harmonic frequencies, it may be driven to do so by the mere existence if the fundamental frequency.

How about a piano? It has an A at 440 hz. The next A up the scale, one octave away, is A 880 (so, you get what an octave is?). Since the peaks of the 440 hz. sound wave occur exactly at the same time as every other peak of the 880 hz. , the sound waves from the lower string tend to make the upper string vibrate at its fundamental frequency, 880 Hz. That's why when you push the damper pedal down on the piano and play one note, you hear others joining in to make a richer sound that consists of the fundamental plus other harmonics.

Now, instruments all tend to have harmonics that are naturally occurring as a result of how they are made. That's why an A on a piano sounds different than an A from an oboe. That's because of the differing amplitude of each harmonic produced by the two different instruments.

Harmonic distortion is the distortion (difference between the output signal and input signal) that is due specifically to the harmonics that the amplification system introduces to the signal. Obviously it "shouldn't" introduce any. But all electronic systems introduce some. And as you read more about all this stuff, you'll find that some harmonics are thought to be more naturally pleasing to the ear than others.

As an aside, note that a "pure" frequency consists of nothing other than a sine wave. Exactly. And considering that, you'll realize that a square wave has tons of harmonics.
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Old 21st December 2002, 05:34 PM   #6
claudio is offline claudio  Italy
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Hello,
take a look at here, it's explained the simple way : http://www.harmony-central.com/Guitar/harmonics.html

Basically harmonics are the differences,in frequency,between the original signal (called fundamental) and the tested signal.
So if the tested sinewave is equal to the fundamental, there are no harmonics; if the tested sinewave has a frequency that is the double of the fundamental frequency , it is called second harmonic; if the tested sinewave has a frequency that is the three times of the fundamental frequency , it is called third harmonic and so on.
To go more deeper, take a look at FOURIER THEORY : everything started from it!!

Regards

Claudio
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Old 21st December 2002, 05:51 PM   #7
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Default Re: What is an harmonic?

Quote:
Originally posted by Bricolo
I always read things about ..th harmonic distortion

but what is an harmonic?
Put 1 kHz sinus wave signal at the input of an amplifier. What do you get at the output? Of course 1 kHz sinus (but a little bit more voltage) ....but... also 2 kHz added and 3 kHz added and 4 kHz added and 5 kHz added etc. This additional tones are added the original input signal. Do you see the pattern? x2, x3 x4 x5 x6 x7 times the input frequency. This additional tones are harmonics to the basic tone. 1% harmonic distorion means that all of the harmonic tones has 1% of the basic signal's amplitude.

Why do you get overtones? The amplifier in not linear. Output (not =) Input*Gain
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Old 21st December 2002, 08:01 PM   #8
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this is a harmonica...
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File Type: jpg harmonica1.jpg (19.9 KB, 235 views)
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Old 21st December 2002, 08:33 PM   #9
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OK, I'll take a stab at it

Mathematics shows us that any waveform you can dream up
can be shown to be made up of various frequencies, each with
its own amplitude and phase. This is called Fourier analysis.

ANY wave form.

If the wave form is repetitive forever, then the spectral
composition will be made up of the frequency of repetition
plus multiples of that frequency.

If the wave is a pure distortionless sine wave, then there is
only that frequency. This makes a convenient test signal,
since if the amplifier distorts, the output will not be a pure
sine wave and there will be additional frequencies, all
multiples of the fundamental sine wave.

Even order harmonics, 2nd, 4th, 6th, etc, represent
distortion which is not symmetric from + to - about the "0"
point, and odd order harmonics, 3rd, 5th, etc, are distortions
which are symmetric above and below the zero point of the
wave.

Distortion analyzers remove the fundamental with a filter
and leave you the harmonics to look at.

Does that help?
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Old 21st December 2002, 08:54 PM   #10
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This sound to me like producing harmonics is the only kind of "distorsion" a amplifier circuit is able to produce. A question, i don´t know if its stupid, but i really don´t understand: what is about mixing the signals? Every Radio employs circuits where one frequency is put in, and mixed with a second frquency and out comes the positive and negative difference (plus the original frequencys) so if i don´t go the usual way to put 1 kHz in the amp and look ´how much 2kHz , 3kHz ... comes out, but i put in 1kHz and 900Hz and look for what i suspect comes out : 100Hz and 1100Hz, 900Hz and 1kHz) ???
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