Is there a "DIGITAL" equivalent of "Q"?
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From: Richard Owlett on 28 Apr 2010 19:30 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 28 Apr 2010 19:35 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 28 Apr 2010 22:08 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 28 Apr 2010 22:56 > > > 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 28 Apr 2010 23:28
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. ����������������������������������������������������������������������� |