Home Theater Forum and Systems banner

1 - 9 of 9 Posts

·
Registered
Joined
·
11 Posts
Discussion Starter · #1 · (Edited)
Just started with REW yesterday! First attempts at measurement seem to indicate something badly wrong with my setup, but I'm flummoxed.

My Setup:
  • MacBook Pro (OS 10.9.5)
  • HDMI out to my receiver, testing one channel at a time as per these instructions
  • USB UMIK-1
  • Sweep 0Hz to 20kHz, -6.0dB, 256k length
  • Mic pointed directly at speaker from listening position for each measurement.

So here are my weird results:
  • "Level is Low, -69dB" warning on all measurements. Though it appears that the mic is working, and there was definitely plenty of sound in the room (see Footnote 1).
  • Impulse response is almost a solid green block.
  • Waterfall shows no significant decay at all. All frequencies appear as if they're ringing indefinitely.
  • All levels pretty low. I had to make my graphs 20dB-105 instead of 45dB-105 or most of the chart would be off the bottom.

Something wrong with my setup? Am I just not reading these charts right? General misunderstanding? Help and advice appreciated. :dontknow:

Footnote 1: I fiddled around with the input gain settings I could find in both REW and my system control panel but could never get the "Low Level" warning to go away. If I cranked my speakers and maxed every input gain setting I could find, that improved the low level warning by about 12 dB. So it was having an effect, which is why I'm confident the mic was returning data.
 

Attachments

·
Super Moderator
Joined
·
9,283 Posts
"Level is Low, -69dB" warning on all measurements. Though it appears that the mic is working, and there was definitely plenty of sound in the room (see Footnote 1).

Footnote 1: I fiddled around with the input gain settings I could find in both REW and my system control panel but could never get the "Low Level" warning to go away.
Sounds like you forgot to do the SPL calibration routine. If you don’t have an outboard sound level meter, you can just play the calibration signal at a comfortable level and “tell” REW that it’s 75 dB.

Regards,
Wayne
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #4 ·
Sounds like you forgot to do the SPL calibration routine.
Well -- I'm feeling like a bit of a dummy, because I can't figure that out. I've tried two different approaches:

Attempted approach #1) Following the instructions in this section of the REW manual, I've opened the SPL meter and clicked the "calibrate" button as suggested. I get the message "SPL Calibration is not required, REW is already calibrated for the USB mic you are using based on the sensitivity data in the mic cal file.

Attempted approach #2) Following the instructions given in this article on using UMIK-1 + HMDI on a mac, I've turned on the generator, opened the SPL meter, and hit the red record button on the SPL meter. The instructions are to "Increase the volume in your A/V receiver or preamp until the level reads about 75 dB." I've swept my receiver through a very wide volume range (from barely audible to near-pain levels) and the SPL meter stays the same, in a range of 68.3 to 68.5. It's not frozen ... it's jittering a bit and clearly a live reading ... but it's not affected by the volume coming out my speakers in any noticeable way.

Results are the same whether I'm using pink noise or 1kHz sine wave from the generator.

you can just play the calibration signal at a comfortable level and “tell” REW that it’s 75 dB.
How do I tell it that the current signal is 75 dB? (Which button/setting?)

Thanks!
 

·
Super Moderator
Joined
·
9,283 Posts
Attempted approach #1) Following the instructions in this section of the REW manual, I've opened the SPL meter and clicked the "calibrate" button as suggested. I get the message "SPL Calibration is not required, REW is already calibrated for the USB mic you are using based on the sensitivity data in the mic cal file.
The first line of the calibration file should be the mic sensitivity information. If not, that’s probably what the problem is. You should be able to download the calibration file from miniDSP.

Regards,
Wayne
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #6 ·
MiniDSP is indeed where I got the cal file. First line looks like this:

Sens Factor =-.478dB, SERNO: 7009549

I tried a few more things last night, and even got a few readings that look reasonable. I'm starting to think the mic has an intermittant problem.

When I cleared the cal file and ran my own calibration, I saw what you meant about telling REW that the level was 75; the place to enter that popped right up.

What I've found is this: the mic tends to produce real data only for a minute or two after first connecting it. I can see the level respond to noise in my system preferences (like if I snap my fingers in front of the mic). During that time, if I run a cal, use the SPL meter, or take measurements during that time I get what looks like real readings. But within a minute or two it stops responding to noise, or if I bump or nudge it at all (even a tiny little bit) it will usually stop producing real output. A couple times it's gotten into weird modes where the SPL was rhythmically bouncing back and forth between two different levels about twice per second, regardless of sound in the room.

So the first day it probably had just already stopped working; I was exploring REW for half an hour after plugging in the mic before I tried recording anything. Last night I got some readings by doing them right after plugging it in, and then disconnecting/reconnecting anytime it stopped working.

I will keep investigating and consider exchanging or replacing the mic if I keep having this much trouble with it.
 

·
Premium Member
Joined
·
1,562 Posts
Be sure the cable is pushed into the mic firmly. I have read here someplace that one of the USB mics (the Umik-1 I think?) needs a firm push to get the plug to snap in completely.
 

·
Registered
Joined
·
363 Posts
Be sure the cable is pushed into the mic firmly. I have read here someplace that one of the USB mics (the Umik-1 I think?) needs a firm push to get the plug to snap in completely.
I agree, it hapenned to me the first time. Push gently but insist a little to put in completly. After a few sessions, no need to insist and all is OK.
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #9 ·
I haven't had opportunity to run more measurements yet but I did check the connection and discovered that yes, I had not pushed it all the way in. I had to push way, way harder than I am usually comfortable doing with small cable connections.

Sorry for the goose chase, if that turns out to have been the problem. But I appreciate all the help!
 
1 - 9 of 9 Posts
Top