A stand will allow for a better phase measurement. At 10Khz, the wavelength is 3.4cm, so 10° phase accuracy is close to 1mm. Such stability over the 5s sweep is impossible to achieve holding the mike with the hand. Also a stand makes the overall measurement process more robust and faster (5-10mn), no need to go back and forth.
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Thanks for your suggestions guys, really much appreciated. I have the stand that shipped with the mike, but how do I use it? In my opinion, a sweep is a fluent move from one position to another, but if I interpret this right, I have to change the mike’s position each time and pause REW, while moving the mike on the stand to the next position? Sorry if I sound dumb, just trying to understand how to do this right…
Guys, do L2-L7 measurements come from sweeps from both speakers or only the left speaker?
It depends what you’re referring to when you say “sweep”. Sweep isn’t a sweeping motion of the microphone. It is an audio sweep.
What I did was generate 2 files with the sweep audio. One left. One right. I loaded them into Roon and played them from there. This allowed me to
1 - test the DAC and amplifier as part of the audio response - not just the speakers.
2 - meant I didn’t have to pulling our cables to give me left or right.
3 - both speakers are on when doing the measurement. If the speaker not in use makes any noise then it will be taken into account. Pulling cables out the amp would effectively kill the speaker.
These seemed to make sense to me. Not that I know much about the subject :).
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Meant the audio sweep. Say at position L3 - do I just measure an audio sweep 20-20000Hz from the left speaker or from both speakers?
At every position (1, 2, 3 up to 9) you need to measure left channel (saved as Lx where x is the position) and right channel (saved as Rx). Do not move the mike between left and right channel measurement. Then move to next position.
This is the best and easier in my view. Just play the sweep files over Roon through your usual audio chain.
Here is a quick guide.
1/ download these two sweep files, unzip and copy to your music Library folder
2/ For your information they look like this, one for left channel, the second for right channel.
3/ Roon should automatically discover them
4/ Make sure DSP engine is disabled
5/ Open the REW album
6/ Position the mike, click on “measure” in REW, make sure all is set like that:
7/ Hit “start measuring” in REW then play via Roon LEFT 256k… sweep
8/ Name recording Lx (x=1 to 9 depending on position, 1 is week spot)
9/ Hist “start measuring” in REW then play via Roon RIGHT 256k… sweep
10/ Name recording Rx
11/ Move mike to next position and repeat from 7
12/ When all measurements are done, save all in a .mdat file
13/ Send .mdat file to Thierry (or put it somewhere in the cloud as it will be probably too big for email)
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Many thanks Alec!.
Getting there, but my impulse response doesnt look right. Do you have a screenshot of the analysis tab under preferences in REW?
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Slight word of caution. Using the files via roon and using a USB mic can make timing tricky. The files I created have the signal at the start to start the impulse recording (looking at yours they seem to have the same) but the USB mics are pretty bad at getting the timing right. Might take a couple of goes (I did it 4 times before they aligned. Shut everything else down on the Mac Mini and keep it consistent between tests.
Hi Alec,
many thanks for the instructions. I will get on this shortly. My AV amp has DIRAC built in so I can compare with that when I get that sorted.
One question though about HAF, how do they compensate for the microphone you use to do the measurements? My AV amp comes with a mic that DIRAC presumably has a known transfer function for. Could I use that for the REW measurements? Alternatively I have a Behringer microphone designed for just this purpose, but could I use it for the measurements for HAF?
http://www.music-group.com/Categories/Behringer/Microphones/Condenser-Microphones/ECM8000/p/P0118
Yeah, thanks Alec. Those instructions are fantastic. I was doing it wrong.
I am still having an issue with my impulse response measurements. Has anyone else done the measurements through Roon-HQPlayer? I wonder if my filter choice with DSD upsampling in HQP is causing the issue.
If you do measurements from outside REW, you need to disable all DSP, up-sampling, filters etc. Playback should be bit-perfect (purple star icon in Roon).
But unless its impractical, I suggest you do the measurements from REW.
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Thanks for that - makes sense. I also have an RME babyface and Behringer microphone, might try again with direct connection from the RME to preamp and bypass my server/dac combo.
So, can confirm bypasing my server/dac and upsampling fixed the measurement problem.
I can see that doing the measurements from REW has advantages (not least with timing) but to my mind playing via roon means you’re measuring the entire signal path not just the speakers. Not so?
When you buy a mic for doing measurements they supply a calibration file for it. With the UMIK-1 for example you go on their website and enter the serial number of your particular mic and download the calibration file. Each mic is tested against a reference before it leaves the factory. Hassle with the mic that comes with your amp is you probably don’t have the calibration file - I guess it is baked into the amp (if they even calibrate them individually).
Lots of mic’s have individual callibration files. The Behringer ECM8000 is similar price to the UMIK-1. I have both, although the behringer was mainly used for recording rather than measuring.
My aim is to correct speaker/room interaction. I dont think the source matters too much in my setup.
I guess that depends on your setup, for me that plays from computer I get the same signal path in both cases, but for more complicated cases it might be preferable to play the sweep from Roon.
Yeah. I was referring to the one that comes with the amp itself - they don’t usually supply calibration files for that.
Wasn’t saying the UMIK was the only one.