Umik 1 with REW vs Old Radio Shack SPL Meter

[darklight]

What do you consider to be more accurate Umik1 with REW or an old analog Radio Shack SPL Meter to set speaker levels?

 

[Wayne A. Pflughaupt]

Technically, REW with a calibrated UMIK-1 should be the equivalent of a laboratory-grade Class 0 meter, which typically are accurate +/- 0.4 dB.

The digital RS meter is rated in its published specs at +/- 2 dB, which is worse than the Class 3 standard of +/- 1.5 dB (there is no Class 4 category).

Regards,
Wayne

 

[darklight]

Technically, REW with a calibrated UMIK-1 should be the equivalent of a laboratory-grade Class 0 meter, which typically are accurate +/- 0.4 dB.

The digital RS meter is rated in its published specs at +/- 2 dB, which is worse than the Class 3 standard of +/- 1.5 dB (there is no Class 4 category).

Regards,
Wayne

Wayne thank you for taking the time to answer my question I really appreciate it.

 

[achugh]

I have a similar question so hopefully using this thread is better than over starting a new one.

I have a calibrated UMIK-1 from Cross Spectrum plus a Galaxy Audio CM-140 SPL meter. When I use REW using the JAVA drivers, the SPL readings shown/plotted varies based on my microphone input level in Windows settings.

How to make sure everything is setup properly? I believe the REW's HELP Documentation and Galaxy Audio both mention that 1Khz signal should read 94db in A weighting to make sure things are calibrated. Galaxy Audio has CM-C200 as the matching calibrator to recalibrate CM-140 in the field which I do not have. I am not sure buying it will help with the REW setup. I do have the Cross Spectrum calibration file for this CM-140 as well to use it as the mic instead of UMIK-1. I was using CM-140 before I purchased UMIK-1.

If I assume my CM-140 is already calibrated (which I know will not use the mic calibration file as the hardware readings use the calibration screw to make changes), how can I make sure what Windows Microphone volume level + Mic Boost setting should I use to make sure my UMIK-1 is at the correct SPL that matches CM-140 and then use this information to add the first line into the Cross Spectrum calibration file? This way going forward REW will know how to properly give me SPL reading.

 

[John Mulcahy]

Do not use mic boost, it is for analog mics plugged into a mic port.

Get the miniDSP cal file for your UMIK-1 and use the sens factor line from that.

 

[achugh]

Hi @John Mulcahy , thank you for responding.

In Windows RECORDING TAB, UMIK-1 allows up to +18db of gain since I have the newer UMIK-1 which goes to +18db instead of the older version that was rated for +12db.

Are you suggesting that I should set the microphone volume level when the reading is 0db (after I have changed the scale to db instead of the windows default to show 0-100 numbers)? Currently I set this number to around 80 which reads as +12db instead of going to 100 volume level of mic which then reads as +18db. This is what I was referring to as the microphone boost.

 

[John Mulcahy]

The 18 dB in the UMIK name is its internal gain and is unrelated to the Windows volume settings. The Windows volume control allows up to 24 dB of gain with a UMIK-1, but it is pointless to use it since it is applied in the digital domain to the digital data and scales noise along with signal, gaining no improvement in S/N and lowering the threshold at which digital clipping occurs. Leave it at 0 dB.

 

[achugh]

@John Mulcahy Thank you for sharing this information.

So in the recording tab, I see

and here this 18db GAIN allowed is all internal to UMIK-1.

When I click on Properties button. I see

which again confirms that the maximum internal gain is 18db

Next I go to LISTEN tab

I believe these default options are correct.

On the LEVELS tab, I was using the following setup

and when switched to DB scale this number 83 on my machine will translate to +12db

If I understood your message correctly, I need to reduce the value down to 0db. Which means I was using the wrong volume on my AVR to get to 75db. Is that correct understanding? Here, I was artificially boosting the SPL value in REW when it was not really at 75 db. In my case all my reading are roughly 12 db higher because once I reduce this volume by 12 db, the values in REW should roughly reduce by 12db too. At that point, I would be roughly increasing my AVR by 12 db to maintain the same SPL across the board.

Finally, my Advanced tab looks like below

 

[John Mulcahy]

If the cal file has the sense factor figure and the input device and input are set for the UMIK-1 REW will read the volume setting and account for it, the REW SPL figure should not be affected by the Windows volume setting. The 0 dB setting provides the widest SPL range without compromising signal-to-noise.