MathGroup Archive 1999

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  • To: mathgroup at
  • Subject: [mg20775] Re: [mg20710] LOW-PASS FILTER
  • From: "Jordan Maclay" <jordanmaclay at>
  • Date: Thu, 11 Nov 1999 00:22:49 -0500
  • Organization: Quantum Fields LLC
  • References: <>
  • Sender: owner-wri-mathgroup at

A low pass filter is a device that removes all frequencies below some
cut-off frequency from a signal that contains many frequencies.  The
simplest example would be found in any beginning electrical circuit text,
and consists of a capacitor and a resistor. The response of the filter to an
applied voltage depends on the fact that the impedance of a capacitor goes
as 1/frequency, so that it tends to short the applied signal at high
frequencies.  A high pass filter, also made from a resistor and capacitor
allows the higher frequencies to pass.

In your case, if you want to remove the noise using a low pass filter, then
you need to add noise that is at a higher frequency than the highest
frequency of interest in your signal.

There are more complicated filters, but the simplest single pole filter that
falls off at 1 db/octave (see EE book) would work fine for you.

good luck...

Jordan MaclayJordan Maclay
Chief Scientist
Quantum Fields LLC
jordanmaclay at

----- Original Message -----
From: Stefanos Xefteris <sxef at>
To: mathgroup at
Subject: [mg20775] [mg20710] LOW-PASS FILTER

> Hi all..
> I have currently taken a project on fourier analysis from a professor of
> mine
> Unfortunately he was very vague about what I have to do.
> He just said that I would take a function(periodic) add noise,and then
> apply a low pass filter on it to eliminate the noise.The problem is I dont
> have a clue about what a low-pass filter is,and he insisted that I should
> find it alone..anyway,if anyone has ann appropriate example,I would be
> glad if he sent it to me

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