Hello,
I'm porting to PD a physical model I created in Matlab. I can't see how to import coefficients and list of numbers from Matlab (i.e. text file) to PD. I need to get these coefficients only once in a while, so a loadbang and several bangs later would be ok.

Example: I have a script in Matlab to calculate SOS (second order section) coefficients for a IIR filter. I can use in PD several [biquad~] blocks to create the IIR, but I don't know how to import coefficients. I can save them as text files in several way (comma delimited, tab delimited, etc) but I can't see how to import them in Matlab and feed it to biquad. And after reading them and storing in an array, what if, for example I have 4x6 coeffs? How do I parse them in order to send 6 coeffs to the first biquad, then 6 to the second and so on?

There seems to be not so much about this on the internet...

Assuming Matlab saves the arrays as each row terminated by a carriage return, you can use [textfile] to open them with the cr option. This will replace the carriage return with a semicolon, which is Pd's method of delimiting lists in a textfile. Then it's just a matter of routing each line in the textfile to a different [biquad~]. You could probably do that by using the same [bang( driving the [textfile] to also drive a [counter], have that

the output of [textfile], and send it through [route] to direct the coefficients to the right [biquad~].

Thanks for the suggestions... I also just discovered about the

... It will be probably easier to use a cascade of to cut away the coefficients for each [biquad]... I will try it out
cheers

I'm encountering a new issue with the biquad and its coefficients.
Matlab and [biquad~] use different notation for the coefficients order, so the coefficients prepared in Matlab should be reordered (this is easier in matlab). But that should be it, and it's not difficult at all. So why are, for example, these Matlab coefficients not working: 0.9784, -1.9781, 1, 1, -1.9781, 0.9784

Let's see: [biquad] needs coefficients fb1 fb2 ff1 ff2 ff3.
The transfer function of the biquad is NUM(z)/DEN(z) with NUM= b0+ b1(z^-1) + b2(z^-1) while DEN=1+ a1(z^-1)+ a2(z^-2).
Ok, so fb1 = a1, fb2 = a2, ff1 = b0, ff2 =b1, ff3 = b2.
I should add that from the equations y(n), w(n) reported in the help probably fb1 = -a1 and fb2=-a2.
Now the coefficients in matlab are instead in the order: b0 b1 b2 1 a1 a2.
That said, the coefficients provided as an example above, converted for biquad would be:
[biquad~ 1.9781 -0.9784 1 0.9784 -1.9781]
Isn't it correct? Now if I feed any signal to such a filter it doesn't produce any sound. Note: as a test I use a [phasor~] as input and a [dac~] as output, I also use [0 0 1 0 0] coefficients, and with these coefficients it works perfectly.
Note: the coefficients I'm using in the example are for an allpass filter.

Any idea? What could be wrong?
Thanks

(not sure about the sign inversion for the fb1 and fb2, but I've also tried without inverting)

I'm no expert in filters, but I believe "fb" and "ff" stand for "feedback" and "feedforward", respectively. So your assumption that fb = a and ff = b makes sense to me. I'm not sure if it will help, but there are some externals in the ggee library that calculate [biquad~] coefficients, such as [highpass], [notch], [lowpass], etc. There doesn't seem to be an [allpass], though. But you could, say, get some high pass filter coefficients from Matlab and compare them to [highpass] and see how they differ, if at all. Might shed some light.

Also, just so you know, reordering lists in Pd is pretty easy. In fact, you could grab single elements from a list without cascading

. Just use message boxes with dollar arguments. For example, if you just wanted the second element of a list, you could do this:

(list)
|
[$2(

and the second element will come out of the message box. Likewise, if you wanted to reorder "b0 b1 b2 1 a1 a2" to "a1 a2 b0 b1 b2", you could do this:

[b0 b1 b2 1 a1 a2(
|
[$5 $6 $1 $2 $3(

thanks useful tips, I'll check out.
Could the biquad implementation be buggy? I'm on Windoze. I may try out on linux as well...

Hi,
the order of the biquad was right, but I manually wrote them down in the wrong way. Now the biquad works.
I have problems in understanding how the textfile sends output.
See attachment: I'm trying to debug the output but I can see no output from textfile or the list split. How should I debug the output of [textfile] without using print?
What does the [textfile] after the [read( message? From the help it seems a mere [bang( should send the lines in output but it doesn't seem so.
Notice: you should input a number on the right inlet, a signal on the left one. The number should be 1-60, better in the range 1-12 since I gave you only one of the txt files.

http://www.pdpatchrepo.info/hurleur/my_APdisp.pd

The txt file to use with the previous pd attachment...

http://www.pdpatchrepo.info/hurleur/disp_biquad_lowtones.txt

hi
You have to send a rewind message before you can read (bang).

mvh

Ok thanks. When the file is read is it automatically outputted? I think not, isn't it?