Measurement volume always low

**Hi Ho** · **07-26-09, 05:19 PM**

Hello. This is my first attempt at using REW. I followed all of the instructions and I'm having a few issues. I am using a RadioShack SPL meter connected via RCA cable to a small Behringer mixer I use to control the speakers on my PC which then goes to the sound card. Both the sound card and SPL meter have been calibrated as per the instructions. The problem is that every time I click on "Measure" and click check levels it always comes back as "Low" (-40db). The SPL meter reads 75db as does the display in REW. After taking the measurement I always get a message saying that the volume was low. I do get a reading but it's all around 60Hz except for a major peak in the 39Hz range where it's at 90. Is my room response really that bad?

My sound card (HT Omega Striker 7.1) is connected via coaxial output to my Yamaha RX-V2700 receiver. When I try to turn the volume up when the pink noise test tone is being output it starts clicking and cutting out. I would describe it as stuttering. I can't turn the volume on the receiver up past -35db without this problem occurring. I have never seen this before. I have run test tones from other programs like TrueRTA and off of test DVDs at much higher levels without problems. Any ideas?

Also, would I be better off using a different microphone? I do live sound for acoustic music and I have some Audio Technica PRO37's and a few ADK A-51 mk5.1's (can't post links). Would one of those be a better measurement tool?

**brucek** · **07-26-09, 07:13 PM**

Quote:

My sound card (HT Omega Striker 7.1) is connected via coaxial output to my Yamaha RX-V2700 receiver

REW is designed to be connected to your receiver with an analog connection only - not digital. How did you calibrate the soundcard if you're using digital? A soundcard calibration involves a loopback cable be connected from analog line-out to analog line-in for the test. This cable is removed once the file is created and then those analog connections of the calibrated channel are used.

Quote:

I am using a RadioShack SPL meter connected via RCA cable to a small Behringer mixer

Why are you connecting through a mixer when the Radio Shack meter already outputs a line-level signal. It is to be connected to the line-in of the soundcard directly.

Quote:

would I be better off using a different microphone?

The Radio Shack meter is perfectly suitable for measurements from 0-3500Hz. You must use the calibration file supplied on our site.

Quote:

every time I click on "Measure" and click check levels it always comes back as "Low" (-40db)

Is the bandwidth you have set in the start and end frequency entries in the Measurement routine consistent with the pink noise chosen in the pulldown for the Settings Check Levels routine.

brucek

**Hi Ho** · **07-26-09, 07:34 PM**

Well I guess I will need to use my laptop then. I didn't even think about the fact that I calibrated with an analog loopback and connected to the receiver via digital. Duh... The desktop I am using is 30 feet from the receiver and I get a nasty ground loop when I use analog connections. It would probably be easier to use my laptop.

It was connected through the mixer because it was easier to reach. The mixer shouldn't alter the signal anyway as it was connected to a line in and the FX send is connected to the sound card line in with the FX send turned all the way up.

Quote:

Is the bandwidth you have set in the start and end frequency entries in the Measurement routine consistent with the pink noise chosen in the pulldown for the Settings Check Levels routine.

I'll have to check that but I believe they were.

**brucek** · **07-26-09, 07:45 PM**

Quote:

Well I guess I will need to use my laptop then.

Note that most laptops don't enjoy a line-in port (which is required for REW). A mic-in port is not suitable. Most users of laptops use REW with an external USB soundcard.

Quote:

It was connected through the mixer because it was easier to reach.

Yep, no problem.

brucek

**brucek2** · **08-02-09, 12:04 AM**

I've got the same, or similar, issue. I'm also using a RS 33-2055 with the calibration file from this site. When I do the "Check Levels..." part of the set up, and turn up my receiver so that the sound meter registers 75db, the input level shows as -31. My sound card input volume is set to 1.000 (max) in every place I've found in my system.

One question... the input meter has both a filled in bar portion that starts from the bottom and grows upwards (which is what hovers at -31), and a single red line that I assume is some sort of peak indicator. The peak indicator is usually around -18. The filled in bar portion never gets anywhere near the single red line. Is this a clue in itself?

--------

(note on username: I'm brand new here, but I've been brucek2 on many other forums for years now. This is the first time I've ever been in a thread anywhere with another "brucek". I'm sorry if it causes any confusion in this community. Funny coincidence.)

**brucek** · **08-02-09, 07:35 AM**

Quote:

Is this a clue in itself?

Not really, the red line is a peak indicator, while the VU meter bars show RMS. We've had members who report the same problem with low input levels, and in the end it appeared to simply be an attribute of the soundcard itself.

Be sure that the cable from the RS meter is proper, and you're using the correct range on the meter (since that affects the voltage output of the meter). If so, you can increase the level of your receiver to measure higher at the RS meter (without changing the range on the meter, such as 80dB). Hopefully that brings the RMS input level up a bit more. Then when you run the Calibrate routine (directly after the Check Levels routine), fool REW by setting the Calibrate thumbwheel to 75dB.

Then carry on as usual with the Measurements.

...the real brucek

**brucek2** · **08-03-09, 02:52 PM**

Thanks brucek. I changed cabling with no difference. Turning up the receiver's volume to reach 80db vs. 75db on the SPL meter did somewhat improve the input level, but not enough to bring it into the desired range. I tried proceeding as you suggested but the measurement I end up with makes no sense to me (shows a red line well above 100db and falling off the top of the screen?)

My soundcard is an ASUS Xonar D2X, in case that matches anyone else's experience.

I ran out of time this weekend, but for next steps I'm thinking I could try:
a) using the built in soundcard on my mobo instead of the Xonar, or
b) returning my SPL meter for another to see if I just got one with abnormally low output

Thanks for the help. All indications are this is an impressive piece of software, here's hoping I can figure out how to make it work in my system.

**brucek** · **08-03-09, 03:12 PM**

You never discussed your soundcard calibration routine results. Did you find that the input level was abnormally low or hard to attain?

Certainly before any measuring is attempted you need to do a soundcard calibration and then measure the loopback cable on the calibrated channel to ensure the result is flat.

Can you comment on how that calibration went, and show me the soundcard calibration graph?

brucek

**brucek2** · **08-03-09, 03:37 PM**

Soundcard calibration struck me as a non-event. I connected soundcard analog out to analog in using a minijackcable. Everything worked per the instructions and the measured input level was very close to the displayed output level without adjustments from me. The calibration graph was basically flat other than the extreme ends.

I'll repeat it tonight so I can reply with more detailed notes and the graph.

**brucek2** · **08-03-09, 11:13 PM**

Measurement from my soundcard calibration is below. Here's how I arrived at it:

1. Deleted all data & settings from REW
2. Plug in loop cable from soundcard analog out to soundcard analog in
3. Go to Settings -> Soundcard -> Measure...
4. The level measurements seemed OK with all the default settings. The meters read:

Code:

     top   -9.0   -8.7   -8.6
bottom -12.0  -11.7 -11.6

5. During measurement, the Headroom was reported at 8.5db

Here's the misc info from the side of the measurement chart:

Code:

Sample rate: 48000Hz
-3dB points: 2.9Hz,  20.866kHz
Input device: No device selected
Input: No input selected
Channel: Right
Input volume: no control
Input RMS target: -12.0dB
Actual RMS at 1kHz: -11.6dB
Output device: No device selected
Output: No output selected
Sweep level: -12.0dB
20Hz .. 20kHz flatness: +0.1, -0.2dB

**brucek** · **08-04-09, 09:12 AM**

From your code box below

Code:

     top   -9.0   -8.7   -8.6
bottom -12.0  -11.7 -11.6

Why are both the left and right VU meters active? A single mono loopback cable is placed on the one right channel (if right selected) and the left channel is not used?

brucek

**brucek2** · **08-04-09, 01:05 PM**

On this last measurement, it was easiest for me to use a stereo loopback cable. I believe I've received the same results using just the right channel in past attempts. I can remeasure just in case.

Intuitively, though, I don't understand why having both channels looped back should produce different results than just a single channel? I'd have expected REW to ignore the extra input on the channel that wasn't being measured.

**brucek** · **08-04-09, 03:29 PM**

Quote:

Intuitively, though, I don't understand why having both channels looped back should produce different results than just a single channel?

The problem I have found is that basically soundcards are junk. The crosstalk and noise is terrible. Whenever I try what you are suggesting I get a lot more noise introduced. I've tried on three different soundcards and have decided that any use of the second channel is a bad idea, including using "left channel as calibration reference" .

brucek

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