Reply by Decay March 4, 20082008-03-04
>Decay wrote: >>> You might find
http://www-users.cs.york.ac.uk/~fisher/cgi-bin/mkfscript
>>> useful. I think a free copy of ScopeDSP from iowegian.com might also. > > ... > >> Thanks Jerry, >> >> These tools are good as the reference as they provide proven results,
but
>> I need something more .. theoretical. I'm looking for some
explanations
>> which will allow me to implement coeffs calculation in c++. > >Download the Java code and figure out what it does. Or get a textbook. > >Jerry >-- >Engineering is the art of making what you want from things you can get. >??????????????????????????????????????????????????????????????????????? >
Oh, I didn't see the link to sources at first: http://www-users.cs.york.ac.uk/~fisher/software/mkfilter Thanks. p.s. it's C actually..
Reply by Jerry Avins March 3, 20082008-03-03
Decay wrote:
>> You might find http://www-users.cs.york.ac.uk/~fisher/cgi-bin/mkfscript >> useful. I think a free copy of ScopeDSP from iowegian.com might also.
...
> Thanks Jerry, > > These tools are good as the reference as they provide proven results, but > I need something more .. theoretical. I'm looking for some explanations > which will allow me to implement coeffs calculation in c++.
Download the Java code and figure out what it does. Or get a textbook. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by Decay March 3, 20082008-03-03
> >You might find http://www-users.cs.york.ac.uk/~fisher/cgi-bin/mkfscript >useful. I think a free copy of ScopeDSP from iowegian.com might also. > >Jerry >-- >Engineering is the art of making what you want from things you can get. >??????????????????????????????????????????????????????????????????????? >
Thanks Jerry, These tools are good as the reference as they provide proven results, but I need something more .. theoretical. I'm looking for some explanations which will allow me to implement coeffs calculation in c++.
Reply by Jerry Avins March 3, 20082008-03-03
Decay wrote:
>> Ooops, sorry Jerry! I missed your original comment citing the same >> source. I was seraching for something else on my own today and stumbled >> onto this very informative site. Then I remembered this thread and >> thought to myself >> "you should put that link on the thread so someone else can benefit from >> it!" >> >> I guess I should spend more time reading before I post! >> >> - Jeff >> > > Jeff, Jerry, > > Thank you. That article is really interesting and R-L filters are quite > popular and useful in audio world, so I'll probably add this to this > "audio tool-set" I'm trying to come up with. > Basically FIR is all done and I'm exploring the Butterworth now. LP is > good and functional(1st and 2nd order and their combination for other > orders), but I'm yet to find how to calculate the coefficients for > high-pass. > So, since you're still viewing this thread, could you please advise or > point to the source with good explanation on this?
You might find http://www-users.cs.york.ac.uk/~fisher/cgi-bin/mkfscript useful. I think a free copy of ScopeDSP from iowegian.com might also. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by Decay March 3, 20082008-03-03
> >Ooops, sorry Jerry! I missed your original comment citing the same >source. I was seraching for something else on my own today and stumbled >onto this very informative site. Then I remembered this thread and >thought to myself >"you should put that link on the thread so someone else can benefit from >it!" > >I guess I should spend more time reading before I post! > >- Jeff >
Jeff, Jerry, Thank you. That article is really interesting and R-L filters are quite popular and useful in audio world, so I'll probably add this to this "audio tool-set" I'm trying to come up with. Basically FIR is all done and I'm exploring the Butterworth now. LP is good and functional(1st and 2nd order and their combination for other orders), but I'm yet to find how to calculate the coefficients for high-pass. So, since you're still viewing this thread, could you please advise or point to the source with good explanation on this? Thanks!
Reply by sparafucile17 March 3, 20082008-03-03
>sparafucile17 wrote: > > ... > >> http://www.rane.com/note160.html > >I sent him that near the beginning of the thread. The filters are >(Butterworth)^2 -- fourth order, but not fourth-order Butterworth. > >Jerry >-- >Engineering is the art of making what you want from things you can get. >����������������������������������������������������������������������� >
Ooops, sorry Jerry! I missed your original comment citing the same source. I was seraching for something else on my own today and stumbled onto this very informative site. Then I remembered this thread and thought to myself "you should put that link on the thread so someone else can benefit from it!" I guess I should spend more time reading before I post! - Jeff
Reply by Jerry Avins March 3, 20082008-03-03
sparafucile17 wrote:

   ...

> http://www.rane.com/note160.html
I sent him that near the beginning of the thread. The filters are (Butterworth)^2 -- fourth order, but not fourth-order Butterworth. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by sparafucile17 March 3, 20082008-03-03
> > >Decay wrote: > >>>First mistake. Don't use FIRs for the audio crossover. >> >> >> Why? > >It is inefficient. The FIR filter for crossover has to be ridiculously >long. It will also introduce the significant amount of delay, which you >will have to compensate by adding the delays to all other channels. > >> IIR instead? > >Yes. A Butterworth of the 4th order will suffice. > >> What about non-linear phase? > >...and the problem with the nonlinear phase is? > >>>Second mistake. The filters are designed either by Remez or by windows.
>>>Remez and windows altogether do not make sense. >> >> >> I'm not sure if it makes sense to gurus, but in my case simple Remez
(at
>> lease as implemented in SPUC) didn't give me zero values at the ends
of
>> the IR. >
Decay, Not sure if you're working on this still or not, but I did find a nice link that talks about the classic IIR cross-over filter topology: Linkwitz-Riley. It basically uses 2 butterworth filters with cut-offs set to the -6dB point instead of the typical -3dB. There's a little more to it but, the link does cover some of the topics discussed here in this thread. http://www.rane.com/note160.html - Jeff
Reply by Vladimir Vassilevsky February 28, 20082008-02-28

Ron N. wrote:


>>>>Don't use FIRs for the audio crossover. >>>Why? >>It is inefficient. The FIR filter for crossover has to be ridiculously >>long. It will also introduce the significant amount of delay, which you >>will have to compensate by adding the delays to all other channels. > > > And if one didn't care about efficiency (the power > required by a dsp which could do this might only be a small > fraction of that used by the amp),
However the cost of the DSP which is able to compute several hundred FIR taps in the real time is a big fraction of the cost of the amp.
> or the delay (one could > even pre-process each speaker channel off-line), then the > problem with experimenting with a linear-phase FIR crossover > would be what? Would it sound bad, or would one be > able to even hear a difference?
There wouldn't be any clear advantage or disadvantage. The trained ear could distinguish the slight difference in the coloration because of the interaction of the highpass and the lowpass crossovers in the areas of overlap. The difference in the speakers is a lot more significant. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by sparafucile17 February 28, 20082008-02-28
>If we get back to phase - humans ears are sensitive to phase (at least at >some frequencies). This can easily be checked by putting some sine wave >into one channel, and the same wave with shifted phase to another and >listening to resulting stereo signal. This will definetely differ from
the
>signal with two coherent channels. >Also, among analog active filters, those with linear phase are valued >most. >Is phase non-linearity of IIRs not audible in real life? > >
In my experience, it would take an "trained ear" to really notice the difference between linear and non-linear phase responses. The average listener is never going to notice the difference. For some reason the research industry is focused in on FIR filter design leaving IIR by the wayside. (mistakenly IMO) Thus a preponderence of papers stating that FIR filters are superior in most ways. The funny thing is if you search hard enough yuo'll find techniques out there that can do the same kind of "tricks" a FIR filter can do using IIR. In my job we develop automotive amplifiers for a bunch of customers and we ONLY use IIR filters. For whatever it's worth I can say manufacturer's like Lexus and Mercedes in their "Luxury" market use IIR filters and I have yet to read an audio review about them that said anything about poor phase response... My 2 cents. Jeff