Python Open Room Correction (PORC)

[Pano]

JL, I did a bit of experimenting with PORC and with "by hand". Both seemed to work pretty well.

To do the correction by hand, I took a measurement with HOLMImpluse then combined that (in HOLM) with my target response. I don't remember which math function I used.
Once that done, I exported a 1/6 octave FR, then re-imported it so that that the FR had the smoothing built in. Not sure that step as necessary, it might not be.
From there I exported the impulse wave for use in a convolver. It worked well. Basically it's doing the same thing as PORC, but with a simple 1/6 octave smoothing. You could choose other smoothing, of course. More steps to go thru than PORC, of course.

Can't say which was better, I didn't do enough listening or measuring. But they did sound similar.

[greenm01]

Originally Posted by jlo

Spline curve calculations are allways tricky : would it be possible to avoid splines ?

I appreciate you pointing this problem out. I will have to dive back into the code and research a better solution: it's definitely something that can be solved.

Do you recommend a particular method or algorithm vs spline?

[jlo]

I would prefer a PCHIP interpolation, see :
http://www.mathworks.com/moler/interp.pdf
http://www.mathworks.fr/help/techdoc/ref/pchip.html
because the points you define are real "corners" for the curve. Spline curves are smoother but can easily give values out of the wished limits.

[hochopeper]

I just had a quick review of scipy docs and seems that an equivalent to matlab's pchip doesn't exist.

A while back this was posted this to a sourceforge mailing list for matplotlib but I've not had time to review it thoroughly to know if it still works or is of use directly in porc without rework I did see some discussion on merging it to mpl but I'm not sure if this has happened or not.

Interesting discussion guys, when I get home from in a few hours I'll have a read and post up anything I can find.

[greenm01]

Originally Posted by hochopeper

I just had a quick review of scipy docs and seems that an equivalent to matlab's pchip doesn't exist

Octave, the open source version of MATLAB, has a pchip function. See attached script from the Octave code base. It's just a matter of porting the function over to Python.

I'll try to set aside some time within the next few days to get it done.... unless someone else beats me to it

[greenm01]

I believe the target curve problem is fixed. Interpolation is not an ideal solution but it seems to work fairly well. If I'm not mistaken this is also the method DRC-FIR employs?

Another option is to simply target a flat curve and use parametric equalization further down the chain. I know this is fairly trivial if one uses OpenDRC or MiniDSP.

Please let me know if anyone finds any other problems or bugs.

[jlo]

Thanks Greenm01 for the update !

but I get following error message from porc.py


Any idea ?

[greenm01]

It appears the latest version of Scipy moved the fft and ifft functions into the scipy.fftpack package. I still have 0.9 installed on my machine where it's located in scipy.signal

I made the update and pushed the revision to Github. It works on my end. Please let me know if you have any other version issues.

[jlo]

Quick and great job Greem01,
seems that everything works fine now, including targets !
I'll have to test more but it's late for me now.

Thanks a lot !

[hochopeper]

Originally Posted by greenm01

I believe the target curve problem is fixed. Interpolation is not an ideal solution but it seems to work fairly well. If I'm not mistaken this is also the method DRC-FIR employs?

Another option is to simply target a flat curve and use parametric equalization further down the chain. I know this is fairly trivial if one uses OpenDRC or MiniDSP.

Please let me know if anyone finds any other problems or bugs.

I just noticed in the update to SciPy 0.11 (released today) that there is some improvements/additions to the interpolate tools - SciPy 0.11.0 Release Notes — SciPy v0.12.dev Reference Guide (DRAFT)

Actually that link is a bit odd - try this - http://docs.scipy.org/doc/scipy/refe...se.0.11.0.html

Also note that there is change to behaviour of the univariate spline in 0.11, it now returns an array, I haven't had a chance to test how this might affect current porc code but worth pointing out that people not wanting to get their hands dirty shouldn't upgrade to 0.11 until that is tested.