creating ideal filters
Jul 18, 2006 at 9:21pm
creating ideal filters
hey – I am working on a project using a bank of filtergraph objects acting as a number of filters…. 9 filters with octave band center freqs of 63, 125, 250 etc. (9 filters, 2 – low pass and high pass, and 7 bandpass)
I am passing pink noise thru the bank of filtergraph objects and have the bandwidth and q set on the filters to be approximately 1 octave wide…
I need to make the filters more of an “ideal filter” where it performs the equalization on only the frequencies contained in the octave band… and not affect the adjacent octave band…
any and all suggestions would be very helpful
Jul 20, 2006 at 1:56am
Check out the buffir~ example in the Max Examples folder (1/3 octave EQ
On Jul 18, 2006, at 5:22 PM, Mark LoRang wrote:
Jul 20, 2006 at 4:14am
i looked into using the fffb~ object and went on to using the filtergraph obj because i needed to have a dynamic gain on the octave band filters.
but the fffb~ could still work… I was checking the Dodge and Jerse book and there is this discussion about filters on pg 180 that says you can cascade multiple bandpass filters to form a filter with steep rolloff but with a wider passband.
can anyone help me on the mathematics here??
how do i best choose the combo of bandpass filter center freqs to create the most “ideal” filter????
Jul 20, 2006 at 4:52pm
You can see this using filtergraph~ with cascade~. Instead of using
I’m not sure how dynamic you need your gain to be, but fffb~ does
On 7/20/06, Mark LoRang
Jul 24, 2006 at 2:58am
hello again –
will cascade~ using filtergraph~ only take filtergraph acting as a bandpass????
i would like to use a combo of highpass, x number of bandpass, and a low pass to try and create these closer to ideal filters…
i can use a number of bandpass filters and tweak their Q and gain and freq and stuff, but it is only allowing bandpass
can i get a lesson on how to better control the filtergraph that is going into the cascade
thanks much for everything
Jul 24, 2006 at 7:55am
> hello again -
maybe it’s time to take a closer look at filtergraph~ inspector.
Jul 25, 2006 at 1:29pm
filtergraph~ inspector simply describes the properties of any individual filter…
how is this supposed to help create ideal digital filters???
anyone and everyone –
can anyone tell me why only bandpass filtergraphs are allowable in cascade????
will all filtergraph signal processing behave like an analog filter??? is there no way to have a square wave shaped eq?? a square wave shaped frequency based signal processing system to split an broadband frequency source into individual octave band components, without affecting the amplitude of the octave bands is what i am looking to create. Any suggestions about how to do this would be greatly appreciated
is there not an object that will act as an ideal filter… in the digital realm, will there always be aliasing that cannot be accounted for????
i need to take a sound source (pink noise, white noise, playback file, etc.) and separate it into nine discrete octave band frequency chunks that will then be equalized by a separate part of my patch. the separation of the original sound signal should happen in a way where the amplitude of the octave band chunks of the broadband signal source are not affected in amplitude at all
thanks for your help and suggestions
Jul 25, 2006 at 3:27pm
> filtergraph~ inspector simply describes the properties of any
seems i misunderstood you.
> can anyone tell me why only bandpass filtergraphs are allowable in
and this seems to be the source of my confusion. don’t know what you
a truly square wave shaped eq is not possible. it’s the same why an
if you want to stick to cascade~ you want some of these in parallel
Jul 25, 2006 at 6:18pm
On 25-Jul-2006, at 15:29, Mark LoRang wrote:
> is there not an object that will act as an ideal filter…
“Ideal” filters are called “ideal” because the word means “existing
What you are looking for is often referred to as a “brick wall”
PS: If you haven’t looked at Forbidden Planet, your time would be
————– http://www.bek.no/~pcastine/Litter/ ————-
Jul 25, 2006 at 7:38pm
thanks for the info, i appreciate it greatly
about the “allowable” thing – i was messing with cascade~ and somehow could only get the number of filters to change, but whenever i adjusted the characteristics of the filter (Q, gain, etc) they switched back to bandpass only
i guess my question is about the message box inputs into the filtergraph~ objects. i need a lesson on how to specify the characteristics of the filter. should i do multiple filtergraph~ object outputs into one cascade or can i do it with a filtergraph with multiple filters inside it?
and yeah, i realize that a exactly shaped square wave – ideal filter is impossible to create…
what i need is a close approximation (evidently better labeled a “brick wall”) to control a broadband noise source in octave band frequency increments. my order of importance of filter quantification areas is 1. roll off, 2. stopband attenuation, 3. phase response, 4. flat passband
the broadband noise source that i am sending thru the eq bank is pink noise or constant noise like from HVAC systems, so i just need the “brick wall”
i’ll check out the trond lossius lead
again, thanks mucho for the info
Jul 26, 2006 at 6:51am
Mark LoRang wrote:
> should i do multiple filtergraph~ object outputs into one cascade or
The latter, the filtergraph~ can talk to cascade~ in its cascade mode.
> and yeah, i realize that a exactly shaped square wave – ideal filter
Hard with biquad~/cascade~s, a brick filter is better done with an fft
a fffb~ with many filters might be also an option…
Jul 28, 2006 at 3:32pm
> i guess my question is about the message box inputs into the
this is covered in the MSPReference.pdf.
> what i need is a close approximation (evidently better labeled a
i think, if you really want to come close to a brick wall, you won’t
1. design (draw or whatever) the desired frequency response
i’ve put together a max-patch based on the above to give an idea of
you can find both patches here:
http://www.esbasel.ch -> downloads
hope this is useful to somebody.
Jul 28, 2006 at 4:12pm
Here is a link to a tutorial on creating an FFT based analyzer. The same technique can be used to create brick wall filters with variable gain on each band.
There is that time/frequency resolution problem when using FFT so I dont know how well this will work for your application. Its worth a shot.
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