# "Export filters impulse as wav" not right?



## Nonlinear (Jun 9, 2012)

I ran a response test of my room with REW, generated the filters, then "exported the filters impulse as wav" file. I loaded that impulse file into SIR convolution plugin and ran some audio.

What I'm hearing from REW sounds very different than the filters generated by DRC Designer. It's almost as if the REW filters are accentuating, rather than correcting, the response variations.

I am going to try and rig up a way to take measurements with the correction filters running to see what's really happening - and which filters are actually correct. 

In the mean time, is it possible the REW "Export Filters Impulse as wav" is actually exporting the _room_ response instead of the filters (a bug)? Or am I doing something wrong?


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## JohnM (Apr 11, 2006)

Nonlinear said:


> is it possible the REW "Export Filters Impulse as wav" is actually exporting the _room_ response instead of the filters (a bug)?


No, but the easiest way to check an impulse response export is to import it back into REW and look at the response.


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## Nonlinear (Jun 9, 2012)

JohnM said:


> No, but the easiest way to check an impulse response export is to import it back into REW and look at the response.


John - thank you for the suggestion.

Now here is what I found - the RED plot is the "correction" filter generated by REW and the green plot is the "correction" filter generated by DRC Designer. As you can see they are VERY different. The filters created by DRC Designer, I'm afraid, actually SOUND right and the REW filters do not.

What am I doing wrong with REW?


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## JohnM (Apr 11, 2006)

REW filtering is mainly aimed at the subwoofer region, the response shown has some very sharp, high gain filters at high frequencies that will certainly make a mess of the sound. Can you post the measurement file you used to generate the filters, and the equaliser, Target and Filter Tasks settings that were used? Did you use any smoothing on the response before generating the filters?


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## Nonlinear (Jun 9, 2012)

John,

Unfortunately I did not save the project after I exported the filters - but I will try to recall what I did. I used a 1/6 smoothing before running the filter generator and a "full range" speaker target setting over the 40Hz-10KHz range.

I know REW is intended primarily for the bass range but I did this just to see what would happen over the full range.

What I find odd is that even in the bass range, one "correction" filter is showing a dip at 200Hz while the other an opposite boost. These look like two completely different rooms/speakers but they were recorded on the exact same setup. All I did was change software programs.

What does all this mean?


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## JohnM (Apr 11, 2006)

Difficult to say without seeing the measurement.


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## shortysock (Oct 8, 2012)

you still need to load the wav file into the audio editor to trim the front and the tail, then inverse the signal to project the opposite of the room.

because when you get all of the room recorded, and you get all of the information without removing layers of it, then the room will completely disappear with enough ability to take you places surreal into a world of story or 'notes' as quick & slick as the drip of existance itself.

it's all about canceling out soundwaves because you throw out the opposite of what it is, as if train tracks in front of the train to allow the thing to roll forward.

there are a lot of convolvers out there that obnoxiously split up the impulse response into two pieces of audio (speaking about the difference between one single sound, compared to one single sound for dry and making people wait for the wet signal with all the important sound data that needs to be there on time to make use of the inversion.
otherwise they are throwing the audio down a hallway and need the delay to get 12ft down the hallway with multiple chained convolution filters going connected to an old atari joystick and a button to set off whether the audio bubble is the only thing in the hallway - or the opposite where the bubble has been cutout and the rest of the hallway is full of audio.

retarded waiting as if you might find it in a theatrical haunted house doing more to satisfy.
because once the haunted house has had it, then the advertisements in the mall speakers are going to want it.
movie theaters would need to rush to it to keep the building paid for by doing the 'master' level thing where other people at home are one level of performance lower.. thus people continue to share with eachother (as if listening to their mouth eating is worth more than the audio of the movie .. i think we agreed to smell eachother, not listening to eachother)

otherwise i need my layers & my reason to turn the thing on and make contact with satisfaction, mixed with feelings of complete.
as if math equations cant be expressed simple with some wires and some switches and some glue all tied in with a plastic toy designed for toddlers.
then they tell me those are the best drivers licenses to get, and the milky cream oat inbetween is a period of wait.. as if the electron worms are extra bigger than necessary.

rew filters sound clean like only the timing is getting calibrated.. because it was already said, if the phase was included the room's physical dimensions would disappear.
if you were in the basement, you would think the dirt behind the wall suddenly yanked on the wall as if some rotating shelf closet in the matrix.
you could fool your brain into thinking there was a backyard with 20ft of room to put your feet up was behind that wall.
a fake window if you will.

a lot to say if you loaded the impulse response file and let it double up the amount of echo rather than cut it.

and dont forget..
if you can get rid of something using the opposite, think about the fundamental ring of the room.. because it should be one piece down in the sub harmonic area, and the opposite of that frequency goes into the negative frequency range.
negative number represents the sub portion of subsonics.
because a single gust of wind is enough to make your skin crawl thinking about something moving at sonic speed.

speakers should be able to hold enough calibrated pressure to form shapes as if a rendering from a projector.
solid enough to bump into and pull you up using a grip around your wrist.
(seeing speakers like tools pepsi & coke gave to the military)


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## Nonlinear (Jun 9, 2012)

I re-ran the setup tonight being very careful not to move anything. The before/after REW EQ response measurements are shown below and are MUCH better. However, it still sounds stange to my ears. Not flat like I expected but actually really strong in the midrange - my full range studio monitors now sound like NS10s!

I guess what I've learned here (and what everybody says) is that the slightest change in location in the room can GREATLY affect the response. So, that being the case, how does one really know what you're hearing?


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## JohnM (Apr 11, 2006)

Nonlinear said:


> I re-ran the setup tonight being very careful not to move anything. The before/after REW EQ response measurements are shown below and are MUCH better. However, it still sounds stange to my ears. Not flat like I expected but actually really strong in the midrange - my full range studio monitors now sound like NS10s!


Big change at the low end, about 15dB in some spots, so bound to sound very different. However, depending on how far away your speakers are and the characteristics of your room a better EQ target is often found to be a gradual tilt downwards from low frequencies to high, so applying a degree of house curve to the response and EQing against that revised target is likely to sound better. 



> I guess what I've learned here (and what everybody says) is that the slightest change in location in the room can GREATLY affect the response. So, that being the case, how does one really know what you're hearing?


Indeed, may also want to read the REW help on the limits of EQ if you haven't already seen that. The strong influence of position on response above the bass range mean EQ is better applied to broad characteristics of the speaker than to the combination of speaker + room, if applied at all, so you would need to measure the speaker as far as you can get it from boundaries and with the impulse response windowed to exclude reflections to see what the underlying speaker response looks like (assuming you don't have an anechoic chamber nearby ). Generally speaking, less is more when it comes to EQ. Your ears and brain are much, much more capable than our measurement systems at distinguishing the direct sound coming from the speaker from the embellishments of the room, things rarely sound as bad as their measurements look.


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## shortysock (Oct 8, 2012)

a house curve should truthfully be known as the impulse response available inside the pocket of air that is between the microphone and speaker.

even if the pocket of air is only half an inch x half an inch .. there would be information in there worth removing for perfect.

my opinion about a flat response is..
each test tone is the same, and after it is all flat, the replacement tones arent the same decibel anymore and it shows up like 3d depth (or use the word texture instead of depth).

when you've got the option of flat, lower treble, higher treble.. there will be a 'preference' for one over the other two by many people.
deviating from reference is really the worst possible thing to do, and viewing the reference point as inaccurate is a shame dispute between the validity of the two people involved.

cutting your ear lobe off is the easiest way to begin an average, because that would place emphasis on the ear canal shape between two different people.
then there is the fact about how two ear canal shapes can hear the same thing differently because of sensitivity in the bloodstream's complexity.
in the final dispute, there would be room modes in the shape of the canal worth agreeing on.
and then once that specific echo is registered, the rest is judgement accuracy.
it doesnt take long for hundreds of people to build and trim down an average.
at best, people would eat something to increase sensitivity across the entire frequency range (a mistake often overlooked) and then making final adjustments as if viewing from a magnifying glass.

just remember how often people dont involve themselves with calibrating or finding an improved reference point.
tight chains on bicycles
proper tire pressure
adjusted cables
better gear ratios

maybe we should blame VHS tapes and the focus tracking, because people learned to leave it alone when it wasnt completely necessary to adjust it.
or
maybe we should blame the overlay that filters the quality of output as any random (or planned) difference, constantly brushing the shore of perfection out of reach.
16bit audio can be quite good at it's maximum potential, but even then you can hear the depth and want more.
imagine getting cleaned up like a resemblence to the word sterile.
imagine sacrificing sterile for something a bit more dirty, but a whole lot more impressive.
or dirty muddy speakers actually capable of providing sterile if only in the right environment.
from dumb dark coal to next door neighbors to the nurse with the sterile wipes.

the reason any portion of the audio is louder than the rest, well it might be because of the phase of the speaker in relation with the phase of the room (air).
but it could, at worst, be distortion in the FFT .. and since it is an inclusion of problem from one or the other.. it is easier to simply look at what was recorded and realize it wasnt recording a bite big enough to reduce the contact of phase from the speaker with the room or air's elasticity.

it shouldnt be difficult to realize what is going on under the hood of rew, and try to avoid pointing at the accuracy of the FFT math going on.

there's phase, but there's also differences in time, and either one could be the reason why the midrange is louder than the other portions of the frequency range.
people get it confused because phase lays itself on top of time and is a thing of its own.

**edit**
maybe cross-spectrum can send out the impulse response file to those who deserve it, as a thing of not necessarily a tax return - but avoiding the problem, thus isolation from prosecution.


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