[sdiy] DSO recommendation please

[cheater cheater]

In that case you are using the scope incorrectly - you should limit
the headroom of the scope - if your sinewave is a +/-5V signal, you
just sample 4.8V...5.2V letting the rest clip. Better yet, you use a
high pass filter and just turn up the sensitivity of the scope. This
applies to any measurement tool/instrument, as precise as they can
get.. it's impossible to make measurements without using a tool
properly, be it adjusting the range or some other parameter. There are
no precise calipers that work for a 12" screw and a 0.002" one.
Besides, this sort of thing is easier to measure with a spectrum
analyzer (it was explained a few days ago on the list how spectrum
analyzers enhance their dynamic range even with normal bit depth
ADC's)

Regarding the waveform reconstruction: generally just a low pass
filter needs to be run on the sampled signal, but the problem is that
it requires 64-bit precision for good quality (especially if you want
to zoom in), and besides it's not something that most people bother
the manufacturer about (because they don't use the scopes at this
level), so they just don't do it, and the scope sells anyway. If you
want good waveform reconstruction, I thik Soundforge has a good
waveform display, Wavelab might too but I've never used it.

D.

On Sun, Apr 4, 2010 at 14:52, Colin f <colin at colinfraser.com> wrote:
>
>
>> Granted, you do have some quantization distortion and noise,
>> but that's at -50dB. It's not like most analog scopes have
>> higher accuracy than 0.5% either :).
>
> So you cant tell the difference on the scope between a pure sinewave, and a
> sinewave overlaid with hideous periodic noise at -48db, and that's assuming
> you have the sinewave perfectly aligned with FSD.
> But you can bet you will hear the difference.
> So what use is the 8-bit scope if it cant show you what you can easily hear
> ?
>
> Cheers,
> Colin f
>
>
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