Forum: GNU Radio Single pole filter, difference equation and documentation.

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Bb3ff9c86361ea921a64632a4c46e824?d=identicon&s=25 Trond Danielsen (Guest)
on 2007-05-11 13:03
(Received via mailing list)
Hi,

I notice from the documentation that all of the different
single_pole_* filters have the same difference equation. Is this
correct?

--
Trond Danielsen
745d8202ef5a58c1058d0e5395a78f9c?d=identicon&s=25 Eric Blossom (Guest)
on 2007-05-11 16:39
(Received via mailing list)
On Fri, May 11, 2007 at 01:01:44PM +0200, Trond Danielsen wrote:
> Hi,
>
> I notice from the documentation that all of the different
> single_pole_* filters have the same difference equation. Is this
> correct?
>
> --
> Trond Danielsen

I was wondering that myself the other day ;)

I haven't had the time to check them out yet.

Eric
D0072e69d706bb3ca211d33a1b536e2c?d=identicon&s=25 Johnathan Corgan (Guest)
on 2007-05-11 18:19
(Received via mailing list)
gr_single_pole_avg filter kernel:

  output = d_alpha * input - d_one_minus_alpha * d_prev_input;
  d_prev_input = input;


gr_single_zero_avg filter kernel:

 output = d_alpha * input + d_one_minus_alpha * d_prev_input;
  d_prev_input = input;


gr_single_pole_iir filter kernel:

  output = d_alpha * input + d_one_minus_alpha * d_prev_output;
  d_prev_output = output;


gr_single_pol_rec filter kernel:

  output = d_alpha * input + d_one_minus_alpha * d_prev_output;
  d_prev_output = output;


So it looks like the first three blocks compute different things but the
fourth is a duplicate of the third.  The difference equation in the
header files is the same for all four, but is only correct for the last
two.

--
Johnathan Corgan
Corgan Enterprises LLC
http://corganenterprises.com
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