[COFF] [TUHS] Monitoring by loudspeaker (was: BTL pranks)

[COFF] [TUHS] Monitoring by loudspeaker (was: BTL pranks)

[@ 2020-07-12 11:58 UTC (permalink / raw)]

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(This should probably be on COFF because I don't think this has much
to do with UNIX.)


On 11 Jul 2020 22:22 -0400, from doug at cs.dartmouth.edu (Doug McIlroy):
> a loudspeaker hooked to the low-order bit of the accumulator played
> gentle white noise in the background. The noise would turn into a
> shriek when the computer got into a tight loop,

How did that work? I can see how tying the low-order bit of the
accumulator to a loudspeaker would generate white noise as the
computer is doing work; but I fail to see how doing so would even
somewhat reliably generate a shrieking sound when the computer is in a
tight loop. Please, enlighten me. :-)

-- 
Michael Kjörling • https://michael.kjorling.se • michael at kjorling.se
 “Remember when, on the Internet, nobody cared that you were a dog?”

[COFF] [TUHS] Monitoring by loudspeaker (was: BTL pranks)

[crossd]

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On Sun, Jul 12, 2020 at 7:59 AM Michael Kjörling <michael at kjorling.se>
wrote:

> (This should probably be on COFF because I don't think this has much
> to do with UNIX.)
>
>
> On 11 Jul 2020 22:22 -0400, from doug at cs.dartmouth.edu (Doug McIlroy):
> > a loudspeaker hooked to the low-order bit of the accumulator played
> > gentle white noise in the background. The noise would turn into a
> > shriek when the computer got into a tight loop,
>
> How did that work? I can see how tying the low-order bit of the
> accumulator to a loudspeaker would generate white noise as the
> computer is doing work; but I fail to see how doing so would even
> somewhat reliably generate a shrieking sound when the computer is in a
> tight loop. Please, enlighten me. :-)
>

I would imagine a cap as a low-pass filter and a transistor as a poor-man's
analog comparator triggering a tape player on loop.

        - Dan C.
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[COFF] [TUHS] Monitoring by loudspeaker (was: BTL pranks)

[fuz]

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When the computer is in a tight endless loop, the accumulator takes the
same series of values every time it's in the loop.  Thus, instead of
white noise you get a sound whose frequency is the clock frequency of
the machine divided by the number of cycles spent by one loop iteration.

That's how you know that the machine is stuck in an endless loop: if it
was doing something useful, the values would change every iteration and
you would get white noise again.

Yours,
Robert C

On Sun, Jul 12, 2020 at 11:58:11AM +0000, Michael Kjörling wrote:
> (This should probably be on COFF because I don't think this has much
> to do with UNIX.)
> 
> 
> On 11 Jul 2020 22:22 -0400, from doug at cs.dartmouth.edu (Doug McIlroy):
> > a loudspeaker hooked to the low-order bit of the accumulator played
> > gentle white noise in the background. The noise would turn into a
> > shriek when the computer got into a tight loop,
> 
> How did that work? I can see how tying the low-order bit of the
> accumulator to a loudspeaker would generate white noise as the
> computer is doing work; but I fail to see how doing so would even
> somewhat reliably generate a shrieking sound when the computer is in a
> tight loop. Please, enlighten me. :-)
> 
> -- 
> Michael Kjörling • https://michael.kjorling.se • michael at kjorling.se
>  “Remember when, on the Internet, nobody cared that you were a dog?”
> 

-- 
()  ascii ribbon campaign - for an 8-bit clean world 
/\  - against html email  - against proprietary attachments

[COFF] Monitoring by loudspeaker

[tih]

Robert Clausecker <fuz at fuz.su> writes:

> When the computer is in a tight endless loop, the accumulator takes the
> same series of values every time it's in the loop.  Thus, instead of
> white noise you get a sound whose frequency is the clock frequency of
> the machine divided by the number of cycles spent by one loop iteration.

A buddy and I did something somewhat related back in the early eighties,
when we were teaching ourselves programming, using, among other things,
his Tandy TRS-80 home computer.  We discovered that a cheap "transistor
radio", sitting close to the computer, would be affected by the noise
generated by it, and then we figured out that if we didn't tune it to a
radio station, we'd get only the noise.  Leaving that on as we worked on
a program, we got familiar with the sound of the code, and became able
to follow the execution by the changing patterns -- and if it did get
stuck in a loop somewhere, we'd not only hear it, but we would also have
a pretty good idea where it happened.

-tih
-- 
Most people who graduate with CS degrees don't understand the significance
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