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difx:highspecres

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How to achieve very high spectral resolution

DiFX can support a wide range of spectral resolutions. Achieving the highest resolutions can be tricky for a number of reasons, many with adverse performance side effects:

  • Typically transform sizes get large
  • Lots of memory is needed / cache memory becomes less effective
  • Bandwidth.time product becomes small (as low as 1), meaning less reduction of data
    • Output data could be larger than input data!
  • Individual FFTs become long (in time), butting up against

Some general tips to consider:

  • Start with small input bandwidths (e.g., plan the experiment properly!)
  • Use factors of 10 in FFT spectral resolution, rather than only factors of 2
    • E.g., set spectral resolution (specRes and fftSpecRes) to 0.001 (MHz) rather than 0.0009765625 (MHz)
  • Make sure integration time (tInt) multiplied by specRes is not less than 0.0000001
  • Make use of zoom band to only save part of the spectrum, if consistent with the science
  • To minimize memory usage, numBufferedFFTs should probably be set to 1 (may greatly hurt performance)
difx/highspecres.1456153079.txt.gz · Last modified: 2016/02/23 01:57 by walterbrisken