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21st December 2002, 03:54 PM  #1 
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What is an harmonic?
I always read things about ..th harmonic distortion
but what is an harmonic? 
21st December 2002, 04:08 PM  #2 
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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 notquiteallthe waylinear gain device.) Erik 
21st December 2002, 05:10 PM  #3 
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21st December 2002, 05:17 PM  #4 
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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. 
21st December 2002, 06:15 PM  #5 
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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 "A440." 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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21st December 2002, 06:34 PM  #6 
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Hello,
take a look at here, it's explained the simple way : http://www.harmonycentral.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 
21st December 2002, 06:51 PM  #7  
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Re: What is an harmonic?
Quote:
Why do you get overtones? The amplifier in not linear. Output (not =) Input*Gain
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21st December 2002, 09:01 PM  #8 
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this is a harmonica...
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21st December 2002, 09:33 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? 
21st December 2002, 09:54 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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