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Hearing ABCs

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GUEST,Bruce O. 21 Mar 01 - 12:13 PM
GUEST,Bruce O. 21 Mar 01 - 05:10 PM
Bert 21 Mar 01 - 05:49 PM
GUEST,Bruce O. 21 Mar 01 - 05:55 PM
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Subject: BS: Hearing ABCs
From: GUEST,Bruce O.
Date: 21 Mar 01 - 12:13 PM

[See earlier thread on 'What do physicists think about' for background]

What are you hearing from ABCs? Got a pretty good oscilloscope late yesterday afternoon.

The speaker in my computer with no input has both input leads at +4.5 VDC. With music (from BASIC's Sound command) one stays put (how, I don't know yet) and the other varies from 4 to 5 VDC.

The SOUND command of BASIC can do stange things to timing.
First, normal music from ABC with ABC2WIN (compiled Visual Basic?) and my ABC player (compiled True Basic). Speaker gets as square wave, 1 V pk-to-pk. Not liking them much, they get a over(under) shoot by about 2.5 V on the leading(trailing) edge, no more than 1 microsecond wide. This is over/under shoot is sometimes called the back emf (from the inductance of the speaker). If not severely damped (as mine is) it's like a slowly dying bell tone, but I get trivial ringing.

100 times through For i = 1 to 100 loop sounding 2KHz for 500 microsecs gives square wave.

100 times through For loop
2KHz, 500 microsecs
1Khz, 1 millisec

Should last .15 secs, but lasts 11 secs. About 37 millisecs of 2KHZ, then 37 millisecs of 1KHz. I don't understand this yet in spite of some other experiments. At what short time does timing go awry?

At any rate the square wave fouls up any experiments based on ear perception of sine waves, because square waves are loaded with odd harmonics

Let x = f*pi*freq
1 pk-to-pk volt square wave is same as:

[2/pi]*[sin(x) + (1/3)*sin(3x) +(1/5)*sin(5x)+ ......]


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Subject: RE: BS: Hearing ABCs
From: GUEST,Bruce O.
Date: 21 Mar 01 - 05:10 PM

Unforgivable above, I left out the factor of time

x = 2*pi*freq*time


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Subject: RE: BS: Hearing ABCs
From: Bert
Date: 21 Mar 01 - 05:49 PM

If I recall back to my BASIC days, the BASIC 'Sound' command simply toggles the speaker on and off at the chosen frequency. I would expect that to give roughly a square wave.

Bert


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Subject: RE: BS: Hearing ABCs
From: GUEST,Bruce O.
Date: 21 Mar 01 - 05:55 PM

That's what I said, giving a little more detail on how.


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