| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 2204.1 | What the heck, give it a stab | VIKING::JANZEN | Tom FXO-01/28 228-5421 MSI ECL Test | Wed Dec 13 1989 14:11 | 35 |
| 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
|
| 2204.2 | oops | VIKING::JANZEN | Tom FXO-01/28 228-5421 MSI ECL Test | Wed Dec 13 1989 14:14 | 9 |
| 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
|
| 2204.3 | Loudness vs Amplitude | WOOF::DRIGIAN | | Wed Dec 13 1989 14:20 | 7 |
| 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
|
| 2204.4 | | VIKING::JANZEN | Tom FXO-01/28 228-5421 MSI ECL Test | Wed Dec 13 1989 15:01 | 7 |
| 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
|
| 2204.5 | What, I Can't Hear You? | DRUMS::FEHSKENS | | Thu Dec 14 1989 08:56 | 11 |
| 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.
|
| 2204.6 | Other thoughts | WOOF::DRIGIAN | | Thu Dec 14 1989 09:26 | 24 |
| 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
|
| 2204.7 | on sirens... | KEYBDS::HASTINGS | | Thu Dec 14 1989 12:53 | 17 |
| 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
|