Date   : Fri, 21 May 2004 19:11:01 GMT 
From   : "Thomas Harte " <thomasharte@...>
Subject: [Electron] sound wave

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Okay, we've discussed the BBC sound wave, but can any electronics people
help me with the Electron 
hardware? The Electron does not have an SN76489, it has a simple single tone
speaker with only two possible 
volumes - 'on' or 'off'. It has a broadly similar capacity as the SN for
turning into a sample generator in that it 
can be set to an inaudible frequency and toggled on and off. My emulator
(ElectrEm) has been able to 
accurately reproduce things like the Exile loading speech for ages, this
isn't really what I want to focus on.

My question is about the actual sound wave. It is my understanding (based
on anecdotal evidence) that the 
little speaker in the Electron is a piezoelectric thing. How do these actually
react to a square wave? Obviously 
we're in the real world so it can't just teleport from high to low (and wouldn't
produce an audible sound if it did), 
but exactly what are its characteristic movements? I was under the impression
that these things are really 
very bad at moving quickly and produce something quite off a square wave
at high frequencies - is that 
accurate?

I'm aware of some old PC and 48kb Spectrum demos that purport to use knowledge
of how similar speakers 
react to state changes to produce higher resolution sound. Although I'm doubtful,
I'd like my emulator to be 
able to reproduce those effects if they exist.

-Thomas

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