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Conference napalm::commusic_v1

Title:* * Computer Music, MIDI, and Related Topics * *
Notice:Conference has been write-locked. Use new version.
Moderator:DYPSS1::SCHAFER
Created:Thu Feb 20 1986
Last Modified:Mon Aug 29 1994
Last Successful Update:Fri Jun 06 1997
Number of topics:2852
Total number of notes:33157

2204.0. "Ode to Harmonics (desc. of even/odd)" by WOOF::DRIGIAN () Wed Dec 13 1989 17:02

    Next question.
    
    What are harmonics???
    What are even order harmonics and odd order harmoics???
    
    This question arises out of my knowledge that a tube amp clips
    on even order harmonics and a transistor amp clips on odd order
    harmonics, therefor (i have been told) the tube amp sounds more
    musical.
    
    
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2204.1What the heck, give it a stabVIKING::JANZENTom FXO-01/28 228-5421 MSI ECL TestWed Dec 13 1989 17:1135
    Models of musical sounds today are getting complicated, but and old,
    simple, useful one that hammond organists learned was that different
    color sounds have different amplitudes of harmonics.
    
    If you played a simple pure tone, it has no harmonics.
    If you play a pure tone of fundamental frequency 440 hertz, the only
    tone in the air is a sine tone of 440 hertz; your ear will distort it
    if it is loud enough.
    If you play a "sawtooth" wave, it has plenty of sine tone harmonics.
    they are called harmonic because their frequencies are integral
    multiples of the fundamental.
    Say you played the tone, the fundamental tone of which is harmonic #1,
    at 440Hz.  The sine wave harmonic components are:
    harmonic#  frequency
    1 	* 440 = 440Hz 
    2 	* 440 = 880Hz
    3 	* 440 = 1320Hz
    4 	* 440 = 1760Hz
    
    A sine wave component is described mathematically by 2 * pi * frequency
    * time.  Time is in seconds and pi = 3.14159265358979...
    The frequency is in this example 440 * harmonic number.
    
    Harmomics 1,3,5,7 are odd harmonics.  harmonics 2,4,6,8 are even
    harmonics.
    
    More recent studies show that real instruments change their harmonic
    content dramatically from instant to instant.  An oboist, for example,
    changes the loudness of harmonics above the fundamental to change the
    apparent loudness, but the amplitude of the fundamental doesn't change
    much; the same is often true of trumpet.  So a loud trumpet and a quiet
    trumpet have different harmonic structures, or probabilities or
    tendencies (to stay the nitpickers).
    
    Tom
2204.2oopsVIKING::JANZENTom FXO-01/28 228-5421 MSI ECL TestWed Dec 13 1989 17:149
    I should have said that a sine component is described by
    sin(2 * pi * f * t)
    = sin( omega * t)
    t is time, pi = 3.14159..., f  = frequency.
    You could also include phase:
    voltage or pressure = sin(omega*t + phi)
    phi=phase, in radians.
    The way sound travels in air is a thermodynamic problem.
    Tom
2204.3Loudness vs AmplitudeWOOF::DRIGIANWed Dec 13 1989 17:207
    RE: 2204.1
    
   Would you please explain the difference between loudness and amplitude.
    I thought that the amplitude of a wave determined it's spl (sound
    pressure level) to the ear or in my terms it's loudness?
    
    Bryon
2204.4VIKING::JANZENTom FXO-01/28 228-5421 MSI ECL TestWed Dec 13 1989 18:017
    I also forgot to mention the amplitude of the harmonics.
    In a sawtooth the amplitude of a harmonic is 1/n times the amplitude of
    the fundamental, where n is the harmonic number.
    Loudness is a sensation of the ear; amplitude is a physical quantity.
    I am guessing that amplitude rises with peak air pressure, but apparent
    loudness is said to rise more slowly in a logarithmic way.
    Tom
2204.5What, I Can't Hear You?DRUMS::FEHSKENSThu Dec 14 1989 11:5611
    re .3 - The problem is that perceived loudness and SPL (a physical
    quantity) are not the same.  Amplitude can be converted to SPL,
    but what the ear and brain do is a different matter.  Perceived
    loudness is a function of frequency content, accommodation, the
    state of your ear, etc.
    
    Notice I keep saying "perceived" loudness.  You can measure it until
    it gets inside your head.
    
    len.
    
2204.6Other thoughtsWOOF::DRIGIANThu Dec 14 1989 12:2624
    Do you know anything about what happens when it gets in your head.  I
    saw a show once that gave a demonstration of what they figured sound
    sounded like befor the ear lobe and structure distorted it.  They
    created a plastic/rubber ear and attacked a mic where the hole to you
    inner ear would be.  They recoreded sound throught the mic and then
    tryed to figure out how much the sound differed from the source, 
    accounting for that difference, they created a recording to play on
    television that was surposed to be tanted to make up for the distortion
    created by the ear. 
    
    All of that accounts for the physical changed created by the outer ear,
    but then what?  Does anybody have a good understaning of how we
    perceive sound?  
    
    I have heard a few things like, we hear logrithmically with respect to
    perceived loudness.  And I have heard that we take spacial clues from
    the front wave of sound.  I fact I have heard of a man that is
    recreating the way a fire/police sirene sounds by creating short mulit
    frequency tone bursts, this is surposed to allow bystanders to
    perceive the location of the oncomming police car better.  
    
    Anybody else have any ideas, comments, CORRECTIONS???
    
    								Bryon
2204.7on sirens...KEYBDS::HASTINGSThu Dec 14 1989 15:5317
    re: the police/fire siren thing
    
    	I heard something on the radio about that. I can't remember the
    guy's name but he called himself a "sound sculptor" What he did was to
    come up with a way of modulating frequencies, that in taking advantage
    of the dopler shift, created a siren that was much more effective in
    doing what sirens should do. (Get people out of the way!)
    	If you were behind, or to the side of, the vehicle with this siren
    you would hear a sort of musical warble. If you were in front of such a
    vehicle (in the way) the sound would contain much more higher
    harmonics. Psycologically the sound seems much more URGENT! In addition
    the wide frequency spectrum used makes it very easy to locate the
    source, hence you don't have to crane your neck around to find it. They
    played simulations of it over the radio. Very effective!
    
    	regards,
    	Mark