From: Richard Owlett on
Mark wrote:
>>
>>> Often folks will say they need a high Q filter when they really mean
>>> they need a high selectivity filter i.e. a filter with small
>>> transition regions.
>> I was explicitly thinking of an RLC network as a band pass filter.
>>
>>
>
> So you are talking about a one pole (one complex pole pair) filter?
>
> Mark
>

Yes, as a first pass at solving my problem.
From: Richard Owlett on
Clay wrote:
> On Apr 26, 3:55 pm, Richard Owlett <rowl...(a)pcnetinc.com> wrote:
>> Please note quotation marks in subject ;)
>> Also, I'm not the oldest on group --- BUT
>> my father operated a *LEGAL* land based spark gap xmtr
>>
>> All that to say that I think in "linear passive discrete" domain
>> rather than in "digital" domain.
>>
>> I have a "filter" problem.
>> I have a reasonable idea on how to implement it.
>> *UNFORTUNATELY* requires HENRY's and FARADs ;/
>> I can write and solve the associated mesh equations
>> My solution will obviously be a subset of SPICE
>>
>> BUT will I be able to describe either
>> PROBLEM or SOLUTION
>> to those educated in digital domain?
>>
>
> Hello Richard,
>
> Certainly if you can describe your problem in terms of poles, zeroes,
> and filter order (i.e., "s" equations), a digital designer can then
> create an approximation to it.
>
> A common example concerns the A,B,C, or D weighting filters in
> acoustics. They are described using analog terms. And a few here have
> talked about how to go from there to digital approximations. So when
> you arrive at your filter, then the same approaches can be used to
> find digital approximations to your filter.
>
> At the following link, you will see some common "s" equations used for
> audio filters.
>
> http://en.wikipedia.org/wiki/A-weighting
>
> While it is true that these transfer functions are they themeselves
> approximations to human phenomina, a digital guy will find an
> approximation to them.
>
> See Al Clark's paper here for a method to make a digital filter have a
> transfer function that matches (within reason) a given mangitude
> function:
>
> http://www.compdsp.com/presentations/Clark/Magnitude%20squared%20method%20to%20solve%20a%20collection%20of%20arbitrary%20functions.pdf
>
>
> IHTH,
> Clay
>
>

Thanks for links. I'll have to dive in to Al's paper. It will
force a refresh on material I haven't looked at for 40 years ;)

From: Jerry Avins on
On 4/28/2010 5:04 PM, Mark wrote:
>
>>
>>
>>> Often folks will say they need a high Q filter when they really mean
>>> they need a high selectivity filter i.e. a filter with small
>>> transition regions.
>>
>> I was explicitly thinking of an RLC network as a band pass filter.
>>
>>
>
> So you are talking about a one pole (one complex pole pair) filter?
How does a pole pair -- complex or otherwise -- become one pole? Even a
pair of coincident poles will have a shape different from a single pole.

Jerry
--
"I view the progress of science as ... the slow erosion of the tendency
to dichotomize." --Barbara Smuts, U. Mich.
�����������������������������������������������������������������������
From: Mark on

>
> > So you are talking about a one pole (one complex pole pair) filter?
>
> How does a pole pair -- complex or otherwise -- become one pole? Even a
> pair of coincident poles will have a shape different from a single pole.
>
> Jerry
> --
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Jerry,

yes I agree with you 100%.

My background is analog and RF and it has been and still is common
practice for analog RF guys to call a filter with 3 LC tuned circuits
a "3 pole filter" even though as you point out this is technically
incorrect and is actually a filter with 3 complex pole pairs.

It took me a while to sort all this out when I was trying to expand my
background from analog RF to include a bit of DSP as well.

So depending on who you are talking to, the vernacular for a tuned
circuit is "a pole" (technically wrong) or more correctly a "complex
pole pair".

I can tell you from experience if you say to some folks, this filter
has 3 complex pole pairs, they will look at you funny and say oh you
mean it has 3 poles...... I say yeah, that's it... :-)

thanks
Mark





From: Jerry Avins on
On 4/28/2010 10:56 PM, Mark wrote:
>
>>
>>> So you are talking about a one pole (one complex pole pair) filter?
>>
>> How does a pole pair -- complex or otherwise -- become one pole? Even a
>> pair of coincident poles will have a shape different from a single pole.
>>
>> Jerry
>> --
> ����������������������������������������������������������������������
> Jerry,
>
> yes I agree with you 100%.
>
> My background is analog and RF and it has been and still is common
> practice for analog RF guys to call a filter with 3 LC tuned circuits
> a "3 pole filter" even though as you point out this is technically
> incorrect and is actually a filter with 3 complex pole pairs.
>
> It took me a while to sort all this out when I was trying to expand my
> background from analog RF to include a bit of DSP as well.
>
> So depending on who you are talking to, the vernacular for a tuned
> circuit is "a pole" (technically wrong) or more correctly a "complex
> pole pair".
>
> I can tell you from experience if you say to some folks, this filter
> has 3 complex pole pairs, they will look at you funny and say oh you
> mean it has 3 poles...... I say yeah, that's it... :-)

Mark,

It wasn't that way when I studied analog electronics (using tubes). Then
we knew that an asymptotic roll-off was 6 dB/octave/pole, and an LC tank
rolls off at 12 dB/octave.

Jerry
--
"I view the progress of science as ... the slow erosion of the tendency
to dichotomize." --Barbara Smuts, U. Mich.
�����������������������������������������������������������������������
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