Guide to using REW with Convolver...

[rajdude]

(under construction)

I looked everywhere but could not find a tutorial or helpfile which describes how to use REW with Convolver. Hence I thought I will start a thread.


First: What is convolver?

Convolver is an Windows application which can be used for Digital Room Correction. It can be used as a plugin for Windows Media player (and other apps).
Full details are here.
A long convolver thread is here.

Second: Where does REW fit into the picture?

REW measures the room's impulse response. That is how it produces the frequency response plots. Then you can (automatically or manuall) setup the filters. After this you can export the impulse responses of filter setups

Step by step guide:

1. Install convolver.
   It is available for download here: http://convolver.sourceforge.net/download.html
   Full instructions are here: http://convolver.sourceforge.net/usage.html
   
   
2. Use REW to generate the Filter Impulse Response file
   
   (This assumes that you already know how to use REW)
   
   • Measure your room’s response
     
     Use the Generic setting for the equalizers. That has the widest range of filter types and the best filter resolutions.
     
   • Create / Adjust filters
     
     You can automatically adjust the filters following the usual REW sequence. REW only auto adjusts filters upto 500hz. If you need to correct room response beyong 500 Hz. you will need to add/ edit the filters manually.
     
     Why does REW not aetup filters automatically all over the 20-20k Hz range? Well, here is what one post says: http://www.avsforum.com/avs-vb/showt...&&#post6966447
     
     

     The peak search function is restricted to lower frequencies as it is looking for modal resonances. Above a few hundred Hz the resonances overlap to such an extent that it si no longer useful to try and correct individual resonances, but you can of course apply broader filters to even out the response. Future versions of the Wizard will address other parts of the range, but that is quite a way off as there is much yet to do for the low frequency range. It is worth bearing in mind that room treatments work very well in these ranges.

   • Export the Channel Filter Impulse Response as WAV file
     
     The File -> Export -> Channel Filter Impulse Response as WAV option generates the impulse response of the filters for the current channel in WAV format, written as 16-bit mono PCM signed data, with the impulse peak normalized to digital full scale.
   
   
3. Use this file in convolver
   
   Basically, you have to point the convolver to the file you just exported above.
   Full details here : http://convolver.sourceforge.net/usage.html
   

That is it !

Until here the setup is simple. But for best sound quality you have use multiple files for multiple channels.

I will quote jrpavel’s post on AVSForum here:
http://www.avsforum.com/avs-vb/showt...&&#post6939704

Others with more experience of room correction may want to chip in, but there are several approaches of increasing complexity.

Assume that you are using stereo, then:

You can measure the impulse response of your left and right speakers separately, and apply the results to the respective channels. The first example on http://convolver.sourceforge.net/configegs.html shows the convolver config file that allows you to do that. Alternatively, you can combine the mono impulse responses into a single stereo WAV file and load that directly instead of using a config file.

That is not, however, the theoretically best way of correcting your system, although it may give good results in practice and has the merit of simplicity. (At least not if you don't listen with a board in front of you that prevents the left channel sound from reaching your right ear ...)

The more correct way, apparently, is to take 4 impulse response measurements (left speaker to left ear, left to right, right to right and right to left) and then apply them using the head-related transfer function (HRTF) network example on http://convolver.sourceforge.net/configegs.html as a model.

I'll leave it to others to comment on / correct this advice, but the long and the short of it is that with convolver you can mix input channels, filter the result, mix/sum the results of different filter paths, and direct them to specified output channels in a completely configurable way. (In fact, I am trying to decide how best to reduce the flexibility, as it makes convolver more complex to set up than is probably strictly necessary.) So, if you want to do other things like split a channel into different frequency ranges and send the results to different output channels, you can do it.

By this time you can also do this with REW:
It will allow a pair of responses to be exported as a stereo WAV. This can be used on convolver for 2 channel audio (stereo)


I will add More later...
Others, please correct me if I am wrong and add tips and questions in this thread.


Here are some more links for further info on this topic:

HTPC and Digital Room Correction :
http://archive2.avsforum.com/avs-vb/...d.php?t=445559

Step by Step guide for using DRC:
http://www.duffroomcorrection.com/im...Guide_v1.0.pdf

In the search for the best parametric eq software for the HTPC...
http://archive2.avsforum.com/avs-vb/...d.php?t=283878

[rajdude]

I am having trouble with exporting the filter WAV file. The option to select a WAV is blank. See below:



And



What am I doing wrong?

[JohnM]

Looks like I broke the export at some point - the list of filter sets for export only contains previous measurements and not the current measurement. If you have no measurements you can export "current settings", if you have more than 1 you can export the settings of the filters for any previous tab but not the latest one. If you only have one measurement you get an empty list. Sorry about that, I'll fix it for the next release.

[rajdude]

Added later..... it works!
Ignore this post!

The problem was that in REW I had opened up the last measurement and applying my filters to it....but when exporting REW was presenting me the earlier measurements....which had no filters !

Stupid me.....just wasted a few hours on this ! I suck !


John,
Thanks ! You are right....with more measurements in REW I am able to export.......just like you described above.

But I am having another issue... When I export the "Filter impulse response as WAV" and use it in convolver....it does nothing... I used a RTA with pink noise to find out that. What's up?

Also is there is nothing in the exported WAV. I mean when I try to play that WAV...I hear nothing.

Whereas I can download some sample IR WAVs here :
http://convolver.sourceforge.net/links.html

When I play them I hear something. Also...... they do work in convolver.

[rajdude]

Ignore this post....see above why.

Here is a test filter which I am having trouble with....

----------------------------------------------------------
Filter Settings file

Room EQ V4.00
Dated: Jul 24, 2007 10:13:25 AM

Notes:

Equaliser: Generic
Jul 23 12:06:10
Full range
Target level: 50.0dB
Filter 1: ON PK Fc 50.0Hz Gain 16.0dB Q 0.493
Filter 2: ON PK Fc 2,987.5Hz Gain -26.0dB Q 0.832
Filter 3: ON None
Filter 4: ON None
Filter 5: ON None
Filter 6: ON None
Filter 7: ON None
Filter 8: ON None
Filter 9: ON None
Filter 10: ON None
Filter 11: ON None
Filter 12: ON None
Filter 13: ON None
Filter 14: ON None
Filter 15: ON None
Filter 16: ON None
Filter 17: ON None
Filter 18: ON None
Filter 19: ON None
Filter 20: ON None

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


The WAV exported from REW is blank.
(see attachment)


Why?

Someone please help me !

[rajdude]

Anyway....I just got it working!
It works amazingly good ! And it is **** simple to do....MUCH MUCH better than using DRC or the long ..lengthy procedure.


You just tweak your filters and export a file to convolver.
and thats it !

Now I have to figure out how to make it work in a Home theater with 7.1 channels of audio.

Thanks a million John! your REW application rocks, big time !
[It would be nice if you can correct that export issue....]

[JohnM]

rajdude wrote:

Thanks a million John! your REW application rocks, big time !
[It would be nice if you can correct that export issue....]

You are very welcome and I fixed the export bug last night so the next release will sort that out.

[terry j]

was always curious about convolver etc etc, but it always made my eyes glaze over ha ha.

The links above led me to read (well, started anyway-not finished yet) the threads on the avs forum on REW and on DRC.

The one on DRC has been archived, which I guess only shows how old it is, the trouble is the guy who started that thread evidently did a big write up on how to use the drc, but the link is no longer active.

SOooo, has that write-up been moved somewhere and is it still available?? I only hope that if it is it is written in such a way that an idiot like me can fumble my way through it.

Rajdude, I would assume that the level of computer knowledge required to successfully get this type of thing up and running is more than required to nut out REW, what is the relative levels of difficulty in your estimation??(only to give me some sort of idea, if the answer is "WWAAAYYY harder dude" then I probably wouldn't even try!!)