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In article <1992Sep30.154718@sdec1.zrz.tu-berlin.de> feiten@sdec1.zrz.tu-berlin.de (Bernhard Feiten) writes:
>
>I'm looking for methods to analyze sounds with DFT.
>Normal window functions have the problem of either having low side lobe level
>or small main lobe bandwidth.

  The "problem of low sidelobe level and small main lobe bandwidth"?
  The lower your sidelobe level, the less spectral leakage problems
  you window will introduce.  The narrower you mainlobe, the better
  your spectral resolution.  The ideal window (an impulse) has no
  mainlobe width and no sidelobes whatsoever.  When creating a
  window, it can be shown mathematically that you will *always*
  trade mainlobe width for reduced sidelobe level, at least in all
  physically realizable windows.

>
>Does anybody knows an algorithm based on DFT (FFT) that optimizes both - 
>for example a main lobe bandwidth similar to a rectangular window and 
>side lobe level similar to a Kaiser-Bessel window ? 

  I refer you to the definitive window reference, 

  "On the Use of Windows for Harmonic Analysis with the Discrete
  Fourier Transform", Frederic J. Harris, Proceedings of the IEEE,
  Vol. 66, No. 1, January, 1978.

  Additionally, for a reference applicable to sidelobe behavior:

  "Some Windows with Very Good Sidelobe Behavior", Albert H.
  Nuttall, IEEE Transactions on A.S.S.P., Vol ASSP-29, No. 1, Feb.
  1981.

  Another good reference for a fascinating window is:

  "A Novel Window for Harmonic Analysis", Fung I. Tseng, Tapan K.
  Sarkar, and Donald D. Weiner, IEEE Transactions on A.S.S.P., Vol
  ASSP-29, No 2, April 1981.

  The latter allows the user the ability to create a very deep notch
  in the sidelobe level at a selectable frequency displacement from
  the main lobe.  Good for harmonic/multitone signals.

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Bob Beauchaine
bobb@vice.ico.tek.com