Randy Yates wrote:> Rune Allnor <allnor@tele.ntnu.no> writes: > >> On 20 Feb, 08:34, "kungcoccos" <c...@hallqvist.biz> wrote: >>> Hi! >>> >>> I would like to create a filter with an inverse sinc-like form in the >>> passband >> What does 'inverse sinc' mean? Are you talking about time domain >> or frequency domain? Do you know how to design FIR filters by >> the window method? If so, how is what you want to do different >> from that method? >> >>> using the most effective algoritm. For now I using fir2, but I >>> suspect that it is not the most cost efficient method. Is it any? >> A somewhat unique problem. Cost efficiency is usually a >> very important issue at the *implementation* stage; cost >> efficiency has not been an issue in design stages for >> decades. > > You're being too pedantic/anal, Rune (good in design, bad in human > interaction). The OP probably meant "implementation efficiency" - it > seems to make more sense given the context.Randy, I expect people to say what they mean, rather than their saying something else and hoping I will guess what they mean. I expect it even more in writing. I try to be sensitive to possible difficulties that people might have with language, but my first inclination is to accept statements at face value. I'm with Rune here. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Arbitrary frequence response
Started by ●February 20, 2008
Reply by ●February 20, 20082008-02-20
Reply by ●February 20, 20082008-02-20
Randy Yates wrote:> Rune Allnor <allnor@tele.ntnu.no> writes: > >> On 20 Feb, 13:36, Randy Yates <ya...@ieee.org> wrote: >>> Rune Allnor <all...@tele.ntnu.no> writes: >>>> On 20 Feb, 08:34, "kungcoccos" <c...@hallqvist.biz> wrote: >>>>> Hi! >>>>> I would like to create a filter with an inverse sinc-like form in the >>>>> passband >>>> What does 'inverse sinc' mean? Are you talking about time domain >>>> or frequency domain? Do you know how to design FIR filters by >>>> the window method? If so, how is what you want to do different >>>> from that method? >>>>> using the most effective algoritm. For now I using fir2, but I >>>>> suspect that it is not the most cost efficient method. Is it any? >>>> A somewhat unique problem. Cost efficiency is usually a >>>> very important issue at the *implementation* stage; cost >>>> efficiency has not been an issue in design stages for >>>> decades. >>> You're being too pedantic/anal, Rune (good in design, bad in human >>> interaction). The OP probably meant "implementation efficiency" - it >>> seems to make more sense given the context. >> If I need to use terms like 'probably' and 'seem' to understand >> a question, I ask for clarifications. If you think that is >> too pedantical then that's your problem. > > I think asking for clarification is good. However, I didn't see you > asking anything with respect to the efficiency issue. What I saw is you > hammering someone for not asking a question in precisely the right way.The way he asked the question was perfectly correct. The only problem, it was the wrong question. (I would likely not have guessed that on my own.) Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●February 20, 20082008-02-20
Vladimir Vassilevsky wrote:> > > kungcoccos wrote: > >> Hi! >> >> I would like to create a filter with an inverse sinc-like form in the >> passband using the most effective algoritm. > > Actually what you need is equalize the frequency rolloff of sinc up to > some frequency, right? This is a typical problem and you can find many > canned solutions. Or you can tackle the problem directly with > Parks-Mclellan or by deconvolution in the time domain.If a DAC is in the signal path, the compensation can often be part of the reconstruction filter. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●February 20, 20082008-02-20
Jerry Avins <jya@ieee.org> writes:> I'm with Rune here.<waves> I'm with helping people rather than bashing them. I like a well-formed question just as much as the next person, and perhaps the OP needs some "correction" in this area, but this group has gotten too unfriendly lately in my opinion. If you aren't in the same corner, then so-be-it. -- % Randy Yates % "Ticket to the moon, flight leaves here today %% Fuquay-Varina, NC % from Satellite 2" %%% 919-577-9882 % 'Ticket To The Moon' %%%% <yates@ieee.org> % *Time*, Electric Light Orchestra http://www.digitalsignallabs.com
Reply by ●February 20, 20082008-02-20
On Feb 20, 9:05 am, Randy Yates <ya...@ieee.org> wrote:> Jerry Avins <j...@ieee.org> writes: > > I'm with Rune here. > > <waves> > > I'm with helping people rather than bashing them. I like a well-formed > question just as much as the next person, and perhaps the OP needs some > "correction" in this area, but this group has gotten too unfriendly > lately in my opinion. If you aren't in the same corner, then so-be-it.I post here for my education and entertainment. (For professional consulting solutions, maybe go see Vladimir or Al, et.al.). If I can't figure out an OP's question, then I might well pick an entertaining or educational mangling of their question, and attempt to comment on or answer such. If that reply has nothing to do with the OP's quest, well, that's what they get for not constraining my imagination with a more clearly or tightly worded (or less homework-problem-looking) description of their situation. For homework questions, I prefer the comp.arch practice of absolutely correct but completely useless answers, if possible. These are often either educational or entertaining to figure out or realize why there are so. IMHO. YMMV. -- rhn
Reply by ●February 20, 20082008-02-20
On 20 Feb, 16:57, Randy Yates <ya...@ieee.org> wrote:> Rune Allnor <all...@tele.ntnu.no> writes: > > On 20 Feb, 13:36, Randy Yates <ya...@ieee.org> wrote: > >> Rune Allnor <all...@tele.ntnu.no> writes: > >> > On 20 Feb, 08:34, "kungcoccos" <c...@hallqvist.biz> wrote: > >> >> Hi! > > >> >> I would like to create a filter with an inverse sinc-like form in the > >> >> passband > > >> > What does 'inverse sinc' mean? Are you talking about time domain > >> > or frequency domain? Do you know how to design FIR filters by > >> > the window method? If so, how is what you want to do different > >> > from that method? > > >> >> using the most effective algoritm. For now I using fir2, but I > >> >> suspect that it is not the most cost efficient method. Is it any? > > >> > A somewhat unique problem. Cost efficiency is usually a > >> > very important issue at the *implementation* stage; cost > >> > efficiency has not been an issue in design stages for > >> > decades. > > >> You're being too pedantic/anal, Rune (good in design, bad in human > >> interaction). The OP probably meant "implementation efficiency" - it > >> seems to make more sense given the context. > > > If I need to use terms like 'probably' and 'seem' to understand > > a question, I ask for clarifications. If you think that is > > too pedantical then that's your problem. > > I think asking for clarification is good. However, I didn't see you > asking anything with respect to the efficiency issue. What I saw is you > hammering someone for not asking a question in precisely the right way.So what? If you take half the time you spend nagging on me and actually check out what the guy in fact asks for, you will find that the matlab function FIR2 is a filter *design* function. Just check out the online matlab docs if you don't have access to the SP toolbox. Since you are so upset about this (and for to settle my own curiosity) -- when was the last time you encountered computational efficiency issues as the main limitation when computing coefficients of filters? Rune
Reply by ●February 20, 20082008-02-20
On Feb 20, 9:39 am, "Ron N." <rhnlo...@yahoo.com> wrote:> On Feb 20, 9:05 am, Randy Yates <ya...@ieee.org> wrote: > > > Jerry Avins <j...@ieee.org> writes: > > > I'm with Rune here. > > > <waves> > > > I'm with helping people rather than bashing them. I like a well-formed > > question just as much as the next person, and perhaps the OP needs some > > "correction" in this area, but this group has gotten too unfriendly > > lately in my opinion. If you aren't in the same corner, then so-be-it. > > I post here for my education and entertainment. (For > professional consulting solutions, maybe go see Vladimir or > Al, et.al.). If I can't figure out an OP's question, then > I might well pick an entertaining or educational mangling of > their question, and attempt to comment on or answer such. If > that reply has nothing to do with the OP's quest, well, that's > what they get for not constraining my imagination with a more > clearly or tightly worded (or less homework-problem-looking) > description of their situation. > > For homework questions, I prefer the comp.arch practice > of absolutely correct but completely useless answers, if > possible. These are often either educational or entertaining > to figure out or realize why there are so.... why they are so, if one wishes an understanding beyond the fill-in-the-blanks answer.> IMHO. YMMV. > -- > rhn
Reply by ●February 20, 20082008-02-20
On 20 Feb, 16:15, Vladimir Vassilevsky <antispam_bo...@hotmail.com> wrote:> kungcoccos wrote: > > Hi! > > > I would like to create a filter with an inverse sinc-like form in the > > passband using the most effective algoritm. > > Actually what you need is equalize the frequency rolloff of sinc up to > some frequency, right? This is a typical problem and you can find many > canned solutions. Or you can tackle the problem directly with > Parks-Mclellan or by deconvolution in the time domain.Since sincs are linear phase, they have zeros outside of, or on, the unit circle, so no causal stable deconv filter can be found in time domain. The best one can do is to find a minimum phase filter which emulates the magnitude response, but that will (if at all possible) come at the price of distorting the deconv'ed sequence in time domain. Rune
Reply by ●February 20, 20082008-02-20
Rune Allnor wrote: [...]> when was the last time you encountered computational > efficiency issues as the main limitation when computing coefficients > of filters?This is a routine situation in my job. 1. I have to compute the coefficients for ~200 IIR sections using a 8-bitter. With all sorts of optimizations, it takes about half of second, and I wouldn't mind if it could be done faster then that. 2. The other problem is the calculation and adjustment of the coefficients on the fly, so the filter is tracking some external input. 3. The third problem is the design of a filter to the arbitrary requirements (by shamanistic optimization). You have to do many iterations. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●February 20, 20082008-02-20
Rune Allnor wrote:> On 20 Feb, 16:15, Vladimir Vassilevsky <antispam_bo...@hotmail.com> > wrote: >>kungcoccos wrote: >> >>>I would like to create a filter with an inverse sinc-like form in the >>>passband using the most effective algoritm. >> >>Actually what you need is equalize the frequency rolloff of sinc up to >>some frequency, right? This is a typical problem and you can find many >>canned solutions. Or you can tackle the problem directly with >>Parks-Mclellan or by deconvolution in the time domain. > > > Since sincs are linear phase, they have zeros outside of, > or on, the unit circle, so no causal stable deconv filter > can be found in time domain.Of course I realize that it is not possible to make a reciprocal of the sinc. However the problem of sinc compensation is very practical if you are dealing with DACs or ADCs. It is often required to have the reasonably flat response, say, to 90% of Nyquist. This implies somewhat +3dB of correction, and this is routinely done by an additional FIR filter. This can also be done in the analog domain (as Jerry suggested), if the phase linearity doesn't matter. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
