The segmented FFT helps with that.  Ideally you have enough segments that there's rarely more than 30-40 dB of flatness variation within any one of them, which is why HFT95 works well and Hann is still usable.

Except in the presence of very strong spurs, most of the energy in the narrowband segments is going to reside in the first few bins.  It's the HPF prior to each FFT stage that keeps that close-in noise from spreading, more than the choice of window function.

-- john, KE5FX
Miles Design LLC

On 6/11/2016 6:33 AM, Attila Kinali wrote:

This gets even better.  The free Pscope software comes with
FFT.  I don't even need to fool with exporting a .file to
some FFT program.

Rick

On Sat, 11 Jun 2016 11:53:22 -0700
"Richard (Rick) Karlquist" richard@karlquist.com wrote:

Good question, I don't really know. And it's a moving target too.

Currently it seems that sigma-delta ADCs reach higher SNR levels
and have less inherent noise. I am not sure whether they are better
at DNL but slighly worse at INL, but from the datasheets I had a look
at it seems so. The advantage of SAR is that they can reach quite
high sampling rates, going up to 15Msps for an 18bit ADC (LTC2387-18).
Though there are sigma-delta that are quite fast, like the AD7760
that can deliver up to 2.5Msps (but only at an SNR of 100dBFS).
Sigma-delta ADCs get worse performance when run faster (they havily
depend on averaging, filtering and noise shaping), while SAR have their
performance almost independent of sampling rate (but the non-linearities
of the internal components get more pronounced with higher sampling rate).
One thing is for sure though: sigma-delta ADCs get you more bits/SNR per buck,
as the high resolution SAR are still quite expensive. SAR ADCs seem to get
better by the day, so it is a good idea to check again what kind of
performance level they reached, once in a while. Sigma-delta do not
develop that fast anymore, but still see some increase in SNR and
sampling rate.

Which one is actually better is not so clear, as a sigma-delta converter
doesn't get to full resulution until you go waaaay down with the sampling
rate (or average). And because the target applications for the two types
of ADCs are slightly different, the datasheets are written differently,
so it's not easy to actually compare their performance. Even more so as
you will be decimating/filtering the samples quite heavily.

I guess for your application, the easiest way is to just buy some
eval boards that seem good and measure their performance directly.

Hmm.. I couldn't find any of the tools I used (back 15 years ago).
But if nothing else works, you can use python (scipy+matplotlib)
or matlab/octave to read the data (all can read wav files)
and plot an fft (shouldn't be more than a couple of lines in any of
those languages). If you get stuck with that, let me know.

		Attila Kinali

--
Malek's Law:
Any simple idea will be worded in the most complicated way.

Hi

I think you will find that you need the DC890 add on board to run Pscope.

Bob