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Using REW and rephase to generate amplitude and time domain corrections


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A short update to mention that, starting with REW 5.17 Beta 14, an XML interface has been substituted to the text file format.

 

To save the filters to the .xml format, just use this function:

Screen Shot 2016-12-04 at 18.16.22.png

The rest of the procedure is unchanged, Pos having changed in rePhase the format of the expected file from REW.

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Hello,

 

Today, I would like to illustrate a slightly different use of REW / rePhase, in the field of simulation, adapted to pedagogy or design of systems.

 

But how can we achieve simulations with rePhase ?

 

It's very simple starting from a blank page, we create a filter, for example high pass like this:

 

Screen Shot 2016-12-07 at 13.25.09.png

 

This filter is a minimum phase filter, and we can generate a pulse from it, for example, with the characteristics on the left of the screen.

 

We will do the same with a linear phase filter of the same characteristics:

 

Screen Shot 2016-12-07 at 13.29.00.png

 

The corresponding pulses are generated and imported into REW by the 'Import Impulse Response' function.

Screen Shot 2016-12-07 at 13.40.48.png

 

From there, we have two filters available in REW, which we can compare the characteristics:

SPL: identical in both cases

SPL_Filtres.jpg

 

Phase: we observe that the phase of the linear phase filter (green on the graph) is equal to zero, which is not the case of the minimum phase filter (red on the graph)

Phase_Filtres.jpg

 

Step: we find the pre-ringing in the case of the linear phase

Step_Filtres.jpg

 

ETC: we find the limit of audibility that I commented on the rePhase forum and which shows that the pre-ringing of the linear filter is probably not audible

ETC_Filtres.jpg

 

Finally, if we represent the excess phase (filter's phase in excess with respect to the minimal phase of the curve), it is observed that the filter in minimal phase behaves better than that in the linear phase, which was expected.

 

MinPhase.jpg

 

LinPhase.jpg

 

With this method, even if you are not at all interested in active correction, but just wanting to simulate the behavior of your speakers, you can go far enough.

 

To illustrate, here is a simulation of the phase of my speakers, with a 2nd order filter at 350Hz and a second at 4000Hz. This is fairly realistic;)

 

BW802.jpg

 

Hope this is useful for some :)

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Hi @pkane2001,

Thanks for your interest in REW/rePhase.

The excess phase is the difference between the minimum phase and the phase actually produced by your system. This difference should effectively be brought back to close to zero in order for your system to behave as a minimum phase system.

As a general rule, you should mainly use the Filters Linearization tag, select the frequencies of your LS crossovers and adjust the slope for each of them. After this step, there should only be some light adjustments to make in the Paragraphic Phase EQ, mainly gentle adjustments in the area of the cross-overs.

If you need help on this, I invite you to join the very friendly and dedicated community which is supporting rePhase here: http://www.diyaudio.com/forums/multi-way/221434-rephase-loudspeaker-phase-linearization-eq-fir-filtering-tool-217.html

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17 hours ago, pkane2001 said:

 

Just as a follow up, here's the corrected speaker output with phase closely matching minimum phase response. I also corrected my HD650 headphone output. Sounds great!

 

phase.thumb.png.81e106bad21489c29a43f12e785a067b.png

 

 

Congratulations ! You did a great job ! Must sound awesomely ;) .

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15 hours ago, lasker98 said:

I'm trying to follow along with SwissBear's pdf tutorial linked above in this thread. I'm having a problem with convolving the rePhase correction impulse to my REW measurement. When I do the convolution with the settings shown (A*B) I end up with a new measurement at 152.9 dB, which is about double the original measurement. At this point, I don't know whether this is wrong (I'm assuming it is) or if it's ok how to I work with it at such an increase amplitude.

 

I've attached a screenshot that should help explain better.

 

Thanks in advance for any help.

Conv Issue.jpg

Nothing wrong here. Just add (in this case subtract) the level which is necessary to obtain a simulated measurement comparable with the original one. On my own system, I subtract 110 db in REW after convolution, but I suspect this is dependent on the level used to make measurements.

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9 hours ago, lasker98 said:

Thanks SwissBear. I assume I do that adjustment in the same window as the convolution? Using the "offset data" setting? That's how I've done it for now.

Yes.

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