I'm using Dasylab and an IOTech 516E Wavebook.
I want to perform an FFT on one of the analogue channels. Because Dasylab will only perform an FFT on a data block that has a length which is a power of 2, I get 'clunky' FFT bin widths if I sample at 50kHz (e.g. 24.4140625Hz with block length of 2048)
If I sampled at 51200Hz or 61440Hz I'd get more sensible integer FFT bin widths (e.g. 25Hz or 30Hz, respectively, with block length of 2048).
Unfortunately the Wavebook can't sample at these frequencies. I've been looking at using the signal adaption module in Dasylab. If I generate a signal in Dasylab at 61440Hz and use this, with the signal adaption module, to 'adapt' my 50 kHz sampling rate, using full interpolation, I get weird noise effects that get worse the closer I get to Fs/2. I suspect there is some aliasing occurring.
If I use signal adaption to interpolate the signal to a very high sampling frequency (e.g. Fs * 128 = 6.4 MHz) then use the separate module to decimate down to the exact required frequency (6.4 MHz /125 = 51200 Hz), the process takes forever. The time between updates of the FFT display is so long it is useless.
Basically, I wouldn't mind a grounding in what the signal adaption module actually does. There isn't a lot of documentation or examples to show how to use it correctly. For instance if I need to filter out noise, where do I place the filter and what value should be used for Fc?
Alternatively, does anybody know any other tricks that I can use to get integer value FFT binwidths in Dasylab?
Thanks,
Andy Phillips
