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Discussion Starter #1
Hi all

A quick (and I think simple!) question from a first-time REW user.

I want to use REW with a Behringer ECM8000 mic and no SPL-meter to check the speaker/room response of my home-audio system. This will be with a view to adding some room-treatment solutions, such as bass-traps and dealing with first-reflection points. I believe there is a thread here where someone was asking about using REW without an SPL-meter.

Anyway, my ECM8000 arrived today and I want to get on with it. Straight away, I have run into a setup issue where I can find no quick answer, either on the Behringer website or anywhere else on the web. The question is:

Where do I point the microphone?!

The mic is omnidirectional, right, so I want to make sure it's picking up room reflections from everywhere, just like my ears would, so is the correct orientation:

A) pointing at the speakers like this:



B) pointing at the ceiling like this:




Looking at the design of the pick-up end of the mic, my gut instinct is B, pointing up, but there are an awful lot of pictures on the web of people pointing them straight at the source...

All answers will be appreciated and respected! :T
 

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Discussion Starter #3
Thanks, Wayne - I really appreciate you taking the time to help out a newcomer like myself!

So I downloaded the ECM8000 calibration file from this site, which you say is calibrated at 0degs, right? So I've gone for the straight at the speakers and angle it up 20degs option. Sorted.

But I'm afraid I now have a couple of follow-up questions (inevitable really, wasn't it?!)

Firstly, the mic is going into the onboard preamp in my RME FireFace400 - do I need to find a calibration file for the soundcard/preamp?

Secondly, I can't see anywhere in the help files to tell me if I need to tick the c-weighted box in the settings when using a microphone. I'm hoping this one is a simple yes/no answer!

Thanks again for taking the time to help a beginner like myself.

Regards
Will
 

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Leave the C weighted SPl meter box unticked. The soundcard response variations are generally very small compared to the mic, it isn't a problem to measure without a soundcard cal file, but doing a loopback measurement of the soundcard is a good way to confirm the basic measurement setup is correct. That needs to be a line out to line in measurement though.
 

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Discussion Starter #5
Leave the C weighted SPl meter box unticked.
Righty-ho.
The soundcard response variations are generally very small compared to the mic, it isn't a problem to measure without a soundcard cal file, but doing a loopback measurement of the soundcard is a good way to confirm the basic measurement setup is correct. That needs to be a line out to line in measurement though.
OK, so I tried a loopback measurement of the soundcard and something appears to be awry. I fed the loop back into the same socket the mic was plugged into, as RME say it can be used for line-level feeds too. But the measurement I get is distinctly un-flat. In fact, it looks a bit like the initial measurements I was getting with the microphone when I was messing around, with what looks like comb-filtering and humps and bumps after 1/3 octave smoothing. I'm sure RME are pretty well respected and it should be impressively flat, so where have I gone wrong?

I am pretty sure there's no feedback loop going on.
I adjusted the level so the peaks were about the same (although the RMS was WAY down on the input meter).
I don't think I can use any other input on the RME, as there's no way to change it in the REW settings (I'm on a Mac).

Help! :help:
 

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Discussion Starter #6
Oh, and I realise this has now moved away from the original thread title - maybe I need a new, more general, "help a confused newbie" type thread?
 

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Did you use a 1/4” TS cable?
No, it's a TRS balanced cable.

I'm beginning to wonder if this is a Mac/Firewire issue.
I tried plugging the loopback into one of the line-inputs (which happens to be input number 5) and ran the measurement again, even though I had no way of telling REW I'd changed the input. Bizarrely I got almost exactly the same result. I'll try with no cable at all...

BTW, maybe now is when I should tell you that it comes up with a warning message at the end of every measurement that says "Measurement may be corrupted - impulse peak is not where it should be", although I assumed this was because I've set the SPL levels roughly by ear, as I don't have an SPL meter.
 

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No, it's a TRS balanced cable.
Line I/O requires a 1/4” TS cable. TRS is balanced I/O.
Leave the C weighted SPl meter box unticked. The soundcard response variations are generally very small compared to the mic, it isn't a problem to measure without a soundcard cal file, but doing a loopback measurement of the soundcard is a good way to confirm the basic measurement setup is correct. That needs to be a line out to line in measurement though.
Regards,
Wayne
 

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There may be bigger problems though, as Java on Macs and Firewire don't seem to get along. Outputs are generated OK but often REW cannot see the Firewire input, even when you have set it up as the default in the Mac's Auio/Midi settings.
 

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Discussion Starter #12
Line I/O requires a 1/4” TS cable. TRS is balanced I/O.
OK, I'll dig around in my cable bag to see if I've got one.

Although, I must say I would have thought it wouldn't make any difference - the RME Fireface 400 is a pretty good quality card, which automatically senses if you're using a balanced or unbalanced connection and adjusts accordingly. Consequently, I would have thought any processing to convert the line level signal to a balanced signal and then back to line level would happen automatically inside the RME.

Anyway, I'll try a TS just in case. :T

BTW, I just tried my demo copy of Fuzzmeasure, and got a nice flat curve from the RME (on loopback with a TRS cable). But Fuzzmeasure doesn't do waterfall plots, unfortunately. SO I really want REW to work, but I'm beginning to suspect it might be a REW/Mac/Multi-channel-firewire-soundcard incompatibility issue...
 

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Discussion Starter #13
There may be bigger problems though, as Java on Macs and Firewire don't seem to get along. Outputs are generated OK but often REW cannot see the Firewire input, even when you have set it up as the default in the Mac's Auio/Midi settings.
This is what I feared, although this seems to suggest there's a workaround.
I tried it though...
 
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