# Can REW create min-phase frd files?



## ernperkins (Jun 23, 2009)

I've used REW to export minimum phase impulse (.wav) files, but it would nice to directly export minimum phase .frd files the same way. I can't find a way to do that except to export a min-phase IR, read it back in and write that out as an .frd file. Am I missing something?

Thanks,
Ed

PS - The two step approach doesn't seem to work either - the resulting .frd file doesn't contain a phase column.


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## JohnM (Apr 11, 2006)

Hi Ed, the two step approach you described is the only way to accomplish this at present, but the .frd file should have phase data - it does when I do it. The steps I followed are:

create the minimum phase version of the measurement
use Export impulse response as wav ticking the box to select the min phase version
use Import impulse response to load the min phase response, then finally
Export measurement as text to save it.


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## ernperkins (Jun 23, 2009)

John - You're correct about the .frd file. I had taken a quick look and expected to see three items (frequency, magnitude and phase) on each line. When I saw only two items per line I assumed the phase was missing. After reading your reply I took a closer look at the .frd file and discovered it has a different format that what I usually work with: the frequency start and step frequencies are in the header and the frequency isn't on each line. 

Unfortunately I don't think my other main tool (Passive Crossover Designer by Jeff Bagby) will recognize this format. Oh well, at least I can transfer IR files (.wav) between REW and HolmImpulse without any problems.

Thanks,
Ed


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## JohnM (Apr 11, 2006)

ernperkins said:


> the frequency start and step frequencies are in the header and the frequency isn't on each line.


That sounds odd - here is what a .frd file normally looks like:


```
* Measurement data saved by REW V5.01
* Source: Line In (PreSonus FireBox WDM), no input selected, Left channel, volume: no control
* Format:  256k Log Swept Sine, 1 sweep at -12.0 dB FS
* Dated: 29-Dec-2011 19:51:09
* REW Settings:
*  C-weighting compensation: Off
*  Target level: 75.0 dB
* Note: Before
* Measurement: Dec 29 19:51:09
* Frequency Step: 0.3364563 Hz
* Start Frequency: 20.187378 Hz
*
* Freq(Hz) SPL(dB) Phase(degrees)
20.187 87.372 -31.619
20.524 89.024 -34.804
20.860 89.142 -41.766
21.197 87.628 -49.130
21.533 83.979 -52.248
21.870 77.411 -31.141
22.206 77.929 32.182
```
Can you attach your .frd file for me to take a look, please?


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## ernperkins (Jun 23, 2009)

John - I repeated everything following your steps below. Upon closer examination it appears that the final step is writing out an impulse file instead of a .frd formatted file. 

create the minimum phase version of the measurement
use Export impulse response as wav ticking the box to select the min phase version
use Import impulse response to load the min phase response, then finally
Export measurement as text to save it.
Here's all the gory details. I should note I'm using REW V5.01 beta 7.

1. The first file is the original measurement. I have REW setup to automatically apply a 3 msec. gate time (right side) so I don't get any room reflections.

2. I then exported the measurement as a wave file (second image).

3. I imported the wave file back into REW (third image).

4. I then compared the freq. response (fourth image) and phase (fifth image) of the original and round-trip (exported, then imported) measurements. There are some differences as you can see. Not sure why, maybe due to my gate time?

Can't seem to upload more files, will continue in next post.....


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## ernperkins (Jun 23, 2009)

Continuing on.....

5. I then exported both the original (first image) and round-trip measurements (second image) as measurement text. The original measurement looks as expected, but the round-trip measurement appears to in IR format. I repeated writing out the round-trip file several times to make sure I hadn't accidentally chosen the wrong format.


Hopefully I'm just making a stupid mistake. And thanks for taking time to look at this.

Ed


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## ernperkins (Jun 23, 2009)

John -

OK - I repeated the above test at work (on my lunch break of course!) using 5.01 Beta 9 and everything seems to work. Also, Beta 9 alerted me that the imported .wav file has the mic and soundcard calibrations turned off - hence the differences I saw in my previous post between the original and imported .wav frequency and phase plots. Once I re-enabled the calibrations both the FR and phase compared.

I'll try using Beta 9 at home tonite with my original files......

Regards,
Ed


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