Re: AUDITORY Digest - 30 Oct 2003 to 6 Nov 2003 (#2003-183)

[Jont Allen <jba@xxxxxxxxxxxxxxxxxx>]

Dear Hafiz
An all-pass filter is only flat if the entire impulse response is
processed. When you take a finite window of a filtered stimulus,
this rule is broken. In a sense, this is equivalent to taking a piece of
the impulse response a(t) and expecting it to have a constant spectrum.
Such a piece of a(t) will not be flat. The longer you make a(t), the
worse the problem becomes.
Hope this helps,

Jont

Automatic digest processor wrote:

> There is one message totalling 46 lines in this issue.
>
> Topics of the day:
>
>   1. why all-pass filter introducing inaudiable magnitude distortion
>
> ----------------------------------------------------------------------
>
> Date:    Thu, 6 Nov 2003 03:20:49 -0600
> From:    hmalik1 <hmalik1@UIC.EDU>
> Subject: why all-pass filter introducing inaudiable magnitude distortion
>
> Dear Experts and Friends,
> I need guidance for understanding the theory behind distortion(inaudible)
> introduced by all-pass filter.....
>
> I'm using 10-14th order all-pass filter(cascade form) with complex pole-zero
> pair close to unit circle i.e.( pole at .9 and zero at 1/.9 and theta = +/-
> phi).
> when a frame of 128-256 audio samples passed through the all-pass filter and
> power-spectrum of the output frame is estimated using
> a) Moving Average signal model
> b) Autoregressive signal model
>
> this is observed that all-pass filter has introduced a local minima in the
> estimated power spectrum at frequency  = phi for both models, but minima in
> model (a) is stronger than model (b).
>
> this distortion introduced by all-pass filter become more stronger as
> pole-zero pair moves close to unit circle or by increasing the order of the
> filter used. (simulation is done using MatLab)
>
> I would appreciate any suggestion or reference that'll help me to understand.
> this behavior .
>
> thanks in advance.
>
> Regards
>
> Hafiz M.A. Malik,
> Multimedia Systems LAB.
> Elecrical & Computer Engineering Dept,
> UIC, Chicago, IL, 60607
> 1(312)4135499
> 1(312)9966007
> hmalik1@uic.edu
> hmalik@uic.edu
> http//multimedia.ece.uic.edu/aslam
>
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>
> End of AUDITORY Digest - 30 Oct 2003 to 6 Nov 2003 (#2003-183)
> **************************************************************