jamin

can anyone help me with implementing an IIR filter, is it possible to use the buffir~ object, i've tried but seem to get no output. regards

iir-using-buffir

IIR filters need feedback (at usually less than the MaxMSP signal 

vector size). Also, most standard MSP objects will not let you do 

feedback directly anyway. The multitap delay objects in MSP allow 

feedback, but the minimum delay length, imposed by the signal vector 

size, is too long for most filtering applications. From what I've 

gathered on this list in recent discussions, cooking one up in Java 

is probably the way to go (That's one of my summer projects, by the 

way....when summer arrives.) unless you are good at coding externals 

in C++ (which is not me....). Personally, I'd love to have a set of 

comb-type objects with accessible feedback loops (for filtering, 

etc.) as MSP standard objects. Meanwhile, have a look at [comb~] and 

[teeth~], among others, to see if they get you where you want to go.

There was some discussion on this general topic a couple months ago 

On Feb 20, 2008, at 6:39 PM, ben Gilman wrote:

> can anyone help me with implementing an IIR filter, is it possible 

> to use the buffir~ object, i've tried but seem to get no output. 

IIR filters need feedback (at usually less than the MaxMSP signal  
vector size). Also, most standard MSP objects will not let you do  
feedback directly anyway. The multitap delay objects in MSP allow  
feedback, but the minimum delay length, imposed by the signal vector  
size, is too long for most filtering applications. From what I've  
gathered on this list in recent discussions, cooking one up in Java  
is probably the way to go (That's one of my summer projects, by the  
way....when summer arrives.) unless you are good at coding externals  
in C++ (which is not me....). Personally, I'd love to have a set of  
comb-type objects with accessible feedback loops (for filtering,  
etc.) as MSP standard objects. Meanwhile, have a look at [comb~] and  
[teeth~], among others, to see if they get you where you want to go.

There was some discussion on this general topic a couple months ago  
in the forum - have a look.

>
> can anyone help me with implementing an IIR filter, is it possible  
> to use the buffir~ object, i've tried but seem to get no output.  
> regards

----
Steven M. Miller
Professor, Contemporary Music Program
College of Santa Fe

Home 
SFIFEM 
Atrium Sound Space 
OVOS 
CMP 


thanks for your response.there is apparently the possibility of using a P4P5 filter in-place of the IIR but im unsure as to how to construct one in Max/Msp.

I'm unfamiliar with the 'P4P5 filter' reference. Perhaps you can 

provide some contextual information about the project you're working 

on and the intended outcome/application? That might give enough info 

p.s. - a brief quote from the email/post to which you are replying 

(i.e., I assume you are replying to my previous response) is helpful, 

particularly to those of us using the email list rather than the 

online forum. See the recent post on discussion threads for more 

On Feb 20, 2008, at 9:05 PM, ben Gilman wrote:

> thanks for your response.there is apparently the possibility of 

> using a P4P5 filter in-place of the IIR but im unsure as to how to 

I'm unfamiliar with the 'P4P5 filter' reference. Perhaps you can  
provide some contextual information about the project you're working  
on and the intended outcome/application? That might give enough info  
to help send you in the right direction.

p.s. - a brief quote from the email/post to which you are replying  
(i.e., I assume you are replying to my previous response) is helpful,  
particularly to those of us using the email list rather than the  
online forum. See the recent post on discussion threads for more  
'user-friendliness' tips.

>
> thanks for your response.there is apparently the possibility of  
> using a P4P5 filter in-place of the IIR but im unsure as to how to  
> construct one in Max/Msp.

Quote: smill wrote on Wed, 20 February 2008 21:27

----------------------------------------------------

> I'm unfamiliar with the 'P4P5 filter' reference. Perhaps you can > provide some contextual information about the project you're 

> working on and the intended outcome/application? That might give > enough info to help send you in the right direction.

A quote makes sense sorry about that, is that a sure fire way to spot a newbie or does the fact it say junior member at the top of every post give it away.

Im attempting to impliment an active noise cancellation system using Max/Msp. The IIR or P4P5 filter is the control filter for the system, i've implemented a FXLMS (Filterd-x least means square) algorithm and that gives me 256 filter weights coefficients for the control filter. Ive attached an image describing the P4P5 filter, im having a hard time picturing how the data flows (at sample level) through the filter.

Quote: smill wrote on Wed, 20 February 2008 21:27
----------------------------------------------------
> Hi Ben,
> I'm unfamiliar with the 'P4P5 filter' reference. Perhaps you can > provide some contextual information about the project you're 
> working on and the intended outcome/application? That might give > enough info to help send you in the right direction.
> Best,
> Steven

Im attempting to impliment an active noise cancellation system using Max/Msp. The IIR or P4P5 filter is the control filter for the system, i've implemented a FXLMS (Filterd-x least means square) algorithm and that gives me 256 filter weights coefficients for the control filter. Ive attached an image describing the P4P5 filter, im having a hard time picturing how the data flows (at sample level) through the filter.
regards,
ben


Does anyone have any thought about constructing the stated P4P5 filter, i don't thoroughly understand the tapped delay lines. any pointers no matter how small would be greatly appreciated. 

Does anyone have any thought about constructing the stated P4P5 filter, i don't thoroughly understand the tapped delay lines. any pointers no matter how small would be greatly appreciated. 
regards  ben 


Do you have a web reference for the design/topology of the P4P5 

filter? If so, I'd be happy to have a look and see if I can help 

explain it. I can't find any info on it doing a simple google search.

On Feb 24, 2008, at 10:21 AM, ben Gilman wrote:

> Does anyone have any thought about constructing the stated P4P5 

> filter, i don't thoroughly understand the tapped delay lines. any 

> pointers no matter how small would be greatly appreciated.

Do you have a web reference for the design/topology of the P4P5  
filter? If so, I'd be happy to have a look and see if I can help  
explain it. I can't find any info on it doing a simple google search.

>
> Does anyone have any thought about constructing the stated P4P5  
> filter, i don't thoroughly understand the tapped delay lines. any  
> pointers no matter how small would be greatly appreciated.
> regards  ben
>

Quote: smill wrote on Sun, 24 February 2008 17:29

> Do you have a web reference for the design/topology of the P4P5 

> filter? If so, I'd be happy to have a look and see if I can help 

> explain it. I can't find any info on it doing a simple google search.

Have you viewed the diagram i attached to one of my previous posts i could email it you if thats any help. Its actually a Non Linear Polynomial (P4P5) Filter. 

Quote: smill wrote on Sun, 24 February 2008 17:29
----------------------------------------------------
> Do you have a web reference for the design/topology of the P4P5  
> filter? If so, I'd be happy to have a look and see if I can help  
> explain it. I can't find any info on it doing a simple google search.

Have you viewed the diagram i attached to one of my previous posts i could email it you if thats any help. Its actually a Non Linear Polynomial (P4P5) Filter. 
regards ben


I didn't see the attachment - I'm on the email list not the forum, so 

it may not have been passed along. Can you email the diagram to me 

On Feb 24, 2008, at 9:07 PM, ben Gilman wrote:

> Have you viewed the diagram i attached to one of my previous posts 

> i could email it you if thats any help. Its actually a Non Linear 

I didn't see the attachment - I'm on the email list not the forum, so  
it may not have been passed along. Can you email the diagram to me  
directly?

On Feb 24, 2008, at 9:07 PM, ben Gilman wrote:
>
> Have you viewed the diagram i attached to one of my previous posts  
> i could email it you if thats any help. Its actually a Non Linear  
> Polynomial (P4P5) Filter.
> regards ben

I'm no expert on filters, but here's my take on the illustration.

From what I can tell from the illustration and info from online, 

this is intended to be a filter for creating a control signal for 

noise control systems, not an audio filter, per se. As such, it may 

not give you anything very useable as a straight audio filter. In any 

case, this is just a particular variant of an FIR filter (i.e. no 

In a nutshell, there are two multi-tap networks, each with their own 

set of summing weights (unspecified, as far as I could find). The 

number of taps in each network is unspecified. The first network is 

fed the input signal raised to the 4th power, the second is fed the 

input signal raised to the 5th power. The summed outputs of each of 

the two multi-tap networks are then summed together to form the 

output (control) signal. I would assume that the weights are chosen 

 From what I can tell from the illustration and info from online,  
this is intended to be a filter for creating a control signal for  
noise control systems, not an audio filter, per se. As such, it may  
not give you anything very useable as a straight audio filter. In any  
case, this is just a particular variant of an FIR filter (i.e. no  
feedback).

In a nutshell, there are two multi-tap networks, each with their own  
set of summing weights (unspecified, as far as I could find).  The  
number of taps in each network is unspecified. The first network is  
fed the input signal raised to the 4th power, the second is fed the  
input signal raised to the 5th power. The summed outputs of each of  
the two multi-tap networks are then summed together to form the  
output (control) signal. I would assume that the weights are chosen  
to sum to unity (1).

>
> Have you viewed the diagram i attached to one of my previous posts  
> i could email it you if thats any help. Its actually a Non Linear  
> Polynomial (P4P5) Filter.
> regards ben

Quote: smill wrote on Mon, 25 February 2008 00:56

> I'm no expert on filters, but here's my take on the illustration.

It is indeed a control filter for a noise cancellation system, im not sure if im understanding the multitap delay in the correct manner. is it a delay as in the next sample within the signal. does the following patch come close to describing its function.

Quote: smill wrote on Mon, 25 February 2008 00:56
----------------------------------------------------
> I'm no expert on filters, but here's my take on the illustration.

I've never used the [buffir~] object, but based on my understanding 

of the MSP manual page, it does not behave like the multi-tap 

networks in the P4P5 filter diagram. (Someone with more experience 

with the [buffir~] object, feel free to chime in!) The [buffir~] 

object performs a convolution of the input signal with each sample of 

A multi-tap network simply sums a number of individual delays (each 

tap is its own delay in parallel with the others) each multiplied by 

A way to do this in MSP would be to use a number of [delay~] objects 

(no feedback needed) set to different delay times, each multiplied by 

the corresponding weight, then summed together.

Hope this helps. I don't have the free time right now to put together 

a patch to illustrate, but hopefully this explanation is clear enough.

On Feb 25, 2008, at 9:17 AM, ben Gilman wrote:

> Quote: smill wrote on Mon, 25 February 2008 00:56

> ----------------------------------------------------

>> I'm no expert on filters, but here's my take on the illustration.

> It is indeed a control filter for a noise cancellation system, im 

> not sure if im understanding the multitap delay in the correct 

> manner. is it a delay as in the next sample within the signal. does 

> the following patch come close to describing its function.

I've never used the [buffir~] object, but based on my understanding  
of the MSP manual page, it does not behave like the multi-tap  
networks in the P4P5 filter diagram. (Someone with more experience  
with the [buffir~] object, feel free to chime in!) The [buffir~]  
object performs a convolution of the input signal with each sample of  
the buffer used as a coefficient.

A multi-tap network simply sums a number of individual delays (each  
tap is its own delay in parallel with the others) each multiplied by  
the weighting coefficient.

A way to do this in MSP would be to use a number of [delay~] objects  
(no feedback needed) set to different delay times, each multiplied by  
the corresponding weight, then summed together.

Hope this helps. I don't have the free time right now to put together  
a patch to illustrate, but hopefully this explanation is clear enough.

>
> Quote: smill wrote on Mon, 25 February 2008 00:56
> ----------------------------------------------------
>> I'm no expert on filters, but here's my take on the illustration.
>
>
> It is indeed a control filter for a noise cancellation system, im  
> not sure if im understanding the multitap delay in the correct  
> manner. is it a delay as in the next sample within the signal. does  
> the following patch come close to describing its function.
>
> regards ben

i suspected the [buffir~] object wouldn't be appropriate. My only issue might be the fact that i need a few hundred taps how cpu intensive will that be? thanks for your description.

Quote: smill wrote on Mon, 25 February 2008 17:03

> I've never used the [buffir~] object, but based on my understanding 

> of the MSP manual page, it does not behave like the multi-tap 

> networks in the P4P5 filter diagram. (Someone with more experience 

> with the [buffir~] object, feel free to chime in!) The [buffir~] 

> object performs a convolution of the input signal with each sample of 

> A multi-tap network simply sums a number of individual delays (each 

> tap is its own delay in parallel with the others) each multiplied by 

> A way to do this in MSP would be to use a number of [delay~] objects 

> (no feedback needed) set to different delay times, each multiplied by 

> the corresponding weight, then summed together.

> Hope this helps. I don't have the free time right now to put together 

> a patch to illustrate, but hopefully this explanation is clear enough.

i suspected the [buffir~] object wouldn't be appropriate. My only issue might be the fact that i need a few hundred taps how cpu intensive will that be? thanks for your description.
regards
ben 

Quote: smill wrote on Mon, 25 February 2008 17:03
----------------------------------------------------
> Hi Ben,
>
> I've never used the [buffir~] object, but based on my understanding  
> of the MSP manual page, it does not behave like the multi-tap  
> networks in the P4P5 filter diagram. (Someone with more experience  
> with the [buffir~] object, feel free to chime in!) The [buffir~]  
> object performs a convolution of the input signal with each sample of  
> the buffer used as a coefficient.
>
> A multi-tap network simply sums a number of individual delays (each  
> tap is its own delay in parallel with the others) each multiplied by  
> the weighting coefficient.
>
> A way to do this in MSP would be to use a number of [delay~] objects  
> (no feedback needed) set to different delay times, each multiplied by  
> the corresponding weight, then summed together.
>
> Hope this helps. I don't have the free time right now to put together  
> a patch to illustrate, but hopefully this explanation is clear enough.
>
> Best,
>
> Steven


I suspect that simple delays with no feedback should be relatively 

efficient, but the only way to know for sure is to try... ;)

On Feb 25, 2008, at 11:23 PM, ben Gilman wrote:

> i suspected the [buffir~] object wouldn't be appropriate. My only 

> issue might be the fact that i need a few hundred taps how cpu 

> intensive will that be? thanks for your description.

I suspect that simple delays with no feedback should be relatively  
efficient, but the only way to know for sure is to try... ;)

>
> i suspected the [buffir~] object wouldn't be appropriate. My only  
> issue might be the fact that i need a few hundred taps how cpu  
> intensive will that be? thanks for your description.
> regards
> ben

and try i will.i may look into using poly~ an object i haven't used but on first inspection it seems it may be possible to use for the quantity of multitaps i need.

Quote: smill wrote on Tue, 26 February 2008 05:12

> I suspect that simple delays with no feedback should be relatively 

> efficient, but the only way to know for sure is to try... ;)

and try i will.i may look into using poly~ an object i haven't used but on first inspection it seems it may be possible to use for the quantity of multitaps i need.
regards ben

Quote: smill wrote on Tue, 26 February 2008 05:12
----------------------------------------------------
> I suspect that simple delays with no feedback should be relatively  
> efficient, but the only way to know for sure is to try... ;)


On Feb 26, 2008, at 2:54 PM, ben Gilman wrote:

> and try i will.i may look into using poly~ an object i haven't used 

> but on first inspection it seems it may be possible to use for the 

I haven't been following this discussion, but I do have a couple 

examples using poly~, and one application that uses it.

The application is called TheMill, and it's a granular playback 

>
> and try i will.i may look into using poly~ an object i haven't used  
> but on first inspection it seems it may be possible to use for the  
> quantity of multitaps i need.

I haven't been following this discussion, but I do have a couple  
examples using poly~, and one application that uses it.

The simple examples can be found here: http://www.xfade.com/max/examples
StupidSynth
PollyWannaAllocate

The application is called TheMill, and it's a granular playback  
thingy, which can be found here:
http://www.xfade.com/max/

> object performs a convolution of the input signal with each sample 

A time-domain convolution is actually combination of delay and gain. 

(but with delay specified in samples, and all samples within the 

window potentially represented) Buffir~ does a time-domain 

convolution, so it is the same thing as a bunch of delay~ objects, 

with the added benefit that you get gain control thrown in for free.

This is the same thing that buffir~ does, except with buffir~ every 

tap is one sample away from the next tap.

That all said, buffir~ is designed for very short IRs (256 samples or 

less). Because it's so short, you're only going to hear its effects 

in the frequency domain, rather than the time domain.

If you needed to sum the last 256 or less samples of your input, you 

could certainly do it with buffir~. On the other hand, if you wanted 

to build a pretty cool comb-filter without feedback, tapin~/tapout~ 

(with lots of integer multiple args) would do the job nicely.

> Hi Ben,
>
> I've never used the [buffir~] object, but based on my understanding  
> of the MSP manual page, it does not behave like the multi-tap  
> networks in the P4P5 filter diagram. (Someone with more experience  
> with the [buffir~] object, feel free to chime in!) The [buffir~]  
> object performs a convolution of the input signal with each sample  
> of the buffer used as a coefficient.

A time-domain convolution is actually combination of delay and gain.   
(but with delay specified in samples, and all samples within the  
window potentially represented) Buffir~ does a time-domain  
convolution, so it is the same thing as a bunch of delay~ objects,  
with the added benefit that you get gain control thrown in for free.

> A multi-tap network simply sums a number of individual delays (each  
> tap is its own delay in parallel with the others) each multiplied by  
> the weighting coefficient.

This is the same thing that buffir~ does, except with buffir~ every  
tap is one sample away from the next tap.

That all said, buffir~ is designed for very short IRs (256 samples or  
less).  Because it's so short, you're only going to hear its effects  
in the frequency domain, rather than the time domain.

If you needed to sum the last 256 or less samples of your input, you  
could certainly do it with buffir~.  On the other hand, if you wanted  
to build a pretty cool comb-filter without feedback, tapin~/tapout~  
(with lots of integer multiple args) would do the job nicely.

> A time-domain convolution is actually combination of delay and gain. 

> (but with delay specified in samples, and all samples within the 

> window potentially represented) Buffir~ does a time-domain 

> convolution, so it is the same thing as a bunch of delay~ objects, 

> with the added benefit that you get gain control thrown in for free.

excellent i suspected the buffir~ object performed as a multitap delay.does that mean that this patch describes the function of the filter at the following link.

https://cycling74.com/forums/index.php?t=getfile&id=1231&rid=0&S=32e9fce9c159425eddbece03c5942629

> That all said, buffir~ is designed for very short IRs (256 samples or 

> less). Because it's so short, you're only going to hear its effects 

> in the frequency domain, rather than the time domain.

All i need is 256 taps with 1 sample delays between, the effects of the filter do not need to be heard as it's a control filter.

> A time-domain convolution is actually combination of delay and gain.   
> (but with delay specified in samples, and all samples within the  
> window potentially represented) Buffir~ does a time-domain  
> convolution, so it is the same thing as a bunch of delay~ objects,  
> with the added benefit that you get gain control thrown in for free.

> That all said, buffir~ is designed for very short IRs (256 samples or  
> less).  Because it's so short, you're only going to hear its effects  
> in the frequency domain, rather than the time domain.

Just an FYI - A primary difference between a true multitap delay and 

convolution with [buffir~] is that each stage in convolution is a 

single-sample delay beyond the previous stage whereas with a multitap 

delay, each individual delay time is independently variable.

It was unclear from the diagram and web-based info I could find how 

many taps were specified and what the delay times were intended to 

be. In retrospect, it could just as well have been a convolution with 

On Mar 2, 2008, at 7:04 PM, ben Gilman wrote:

>> A time-domain convolution is actually combination of delay and gain.

IIR using buffir~