export impulse response normalization issue

nc535

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I'm using REW with VituixCAD to create equalization filters for JRiver. Jriver wants/needs a filter with nominally unity gain. I import mono filters from Vituix into REW, use REW add offset to data to set 1khz level to 0 db at 1 khz for both left and right channels, then export the pair of filters as a stereo.wav. No matter whether or not I check normalize in the export dialog, the exported filter has an SPL of around 150 db when I bring it back into REW to check the gain. How can this be happening when the original filters had nominally 0 db gain there and less than 20 db boost at the extremes of the spectrum?

Strangely, JRiver is able to play it despite the large filter gain even without Jriver normalization turned off, but there is a large difference between output straight vs through Jriver and non-Jriver output that I would like to eliminate by setting the gain of these filters appropriately.

I guess my question boils down to is there a way to export a filter.wav with a specific gain at the center of the passband?

Thanks in advance for your help!
 

John Mulcahy

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Adding an offset to the response data doesn't affect the IR values, and even if it did that would be lost when normalising since that divides everything by the peak value.

When REW imports an IR it doesn't know the relationship between the data values and SPL so it uses the current measurement SPL offset figure. If the IR was normalised or if it didn't come from a measurement that will produce very high SPL figures. That doesn't mean the IR has a lot of gain.

If you are exporting EQ filter impulse responses exporting them as 32-bit float without normalisation should give an IR that will provide the gain the EQ filter response showed on the Filter adjustment graph.
 

nc535

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Thanks. That is obvious when you point it out. My preconceptions got in the way of understanding. Vituix does show a filter response curve and the ones exported from REW do have unity gain.
 
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huibuh1001

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Hi, lets piggyback here. I wonder a bit if it is right to use normalization if I export stereo filters. Do they fit together then?
 

John Mulcahy

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As above, if you want to preserve the nominal (and relative) gain of the filter sets export them as float without normalisation.
 
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