[LAD] Real-time plotting of audio/ oscilloscope.

[fons at kokkinizita.net]

On Thu, Jun 17, 2010 at 10:53:31PM +0200, Nick Copeland wrote:
> 
> How do the other scopes work? If you really want to get a good image of
> a waveform on a screen then you might want to totally divorce the sampling
> rate from the screen drawing:

Yes. For a soft scope you have two options: a horizontal scale
caibrated in 'samples' (a pixel corresponds to an integer number
of samples), or one that maps to time (in ms or us).

> To actually see a waveform and how it develops then you really need the scope
> to sync to it. The way the oscilloscopes worked was a detection level at which 
> to start painting (positive edge zero crossing for example but other levels are
> equally acceptable) and a delay time before searching again (blanking period,
> more or less).

In a digital scope finding the sync point requires upsampling by a least
a factor of four, then you can interpolate linearly. After that, to 
display the actual waveform correctly aligned to the sync point you may
have to interpolate even to a finer level. It's not at all a simple
thing.

Ciao,

-- 
FA

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