# [FieldTrip] Hann taper vs. single Slepian taper

David Groppe dgroppe at cogsci.ucsd.edu
Mon Dec 20 14:21:42 CET 2010

```Thanks very much for the helpful emails Ingrid & Robert.
-David

On Mon, Dec 20, 2010 at 3:59 AM, Robert Oostenveld
<r.oostenveld at donders.ru.nl> wrote:
> To complement Ingrids good explanation: the shape of the Slepian tapers
> depend on how many you compute, i.e. if you compute one it will have a
> (slightly) different shape that the first one if you compute four. The first
> Slepian taper never goes exactly to zero at the edges, whereas the Hanning
> (or Hann, as it is also called) does. The consequence is that a single
> Slepian leaks more than a Hanning. The reason for using a Hanning taper is
> typically that you don't want to spectrally smooth (usually because the time
> window is already on the short side), so the leakage of a single Slepian is
> in that case not desired.
>
> Robert
>
>
>
>
> On 18 Dec 2010, at 1:13, Ingrid Nieuwenhuis wrote:
>
>> Dear David,
>>
>> The Slepian tapers are sets of multiple (orthogonal) tapers, that only
>> combined accomplish this "optimally maximized frequency resolution while
>> minimizing leakage from distant frequencies". If you use only a single
>> taper, the Slepian taper is suboptimal compared to the Hanning taper. I've
>> attached some teaching slides I have with some background on multitapers.
>>
>> Hope this helps,
>> Cheers,
>> Ingrid
>>
>>
>> On 12/16/2010 6:01 AM, David Groppe wrote:
>>>
>>> Hi Fieldtripians,
>>>   Could anyone explain to me when, if ever, it would be better to
>>> perform a DFT with a Hann taper vs. a single Slepian taper?  It was my
>>> understanding that Slepian tapers in general optimally maximized
>>> frequency resolution while minimizing leakage from distant
>>> frequencies.  However, a colleague of mine says he was told at a
>>> workshop at the Donders Institute that a Hann taper was better than a
>>> single Slepian taper (if you are only going to use one taper).
>>>            -David
>>>
>>
>> --
>> Ingrid Nieuwenhuis PhD
>> Sleep and Neuroimaging Laboratory
>> Department of Psychology
>> University of California, Berkeley
>> California 94720-1650
>>
>> <multitapers.pdf>_______________________________________________
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>
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--
David Groppe, Ph.D.
dgroppe at cogsci.ucsd.edu
http://www.cogsci.ucsd.edu/~dgroppe/

```