# REW UMIK 1 and AV Preamp Calibration Setup



## AVSION (Sep 11, 2016)

Hi,

I would like to use REW to tune my home theatre system and room acoustics, but i need some help understanding how to setup it up for best results.
I have Marantz AV7702 MKII Preamp connected to EMOTIVA XPA5 GEN3 amplifier and focal 5.1 speakers system. i purchased UMIK 1 mic and miniDSP 2x4(for the subwoofers..2 SVS PB2000 coming soon:smile to use it with REW on my samsung laptop running window 10.
From the research i did, best way is to connect the UMIK to the computer input using the USB cable, for the output i will use the HDMI from the laptop to connected to the Marantz HDMI inputs and set the DSP to 5.1 . using this setup the signal from the laptop will be going through the marantz to the AMP and finally to the speakers. 

my question, as the signal going through the marantz preamp does it need to be calibrated (same process when doing a loopback on interface) to make sure i get accurate results? if so how would you calibrate the preamp with REW? or is it better as a second option(prefer not to start unplugging RCAs) to use the miniDSP 2x4 analog IO ,instead of the Marantz preamp, straight to the AMP? and do i need to calibrate the miniDSP 2x4 with REW?

Hope it make sense

Thank you


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## AudiocRaver (Jun 6, 2012)

AVSION said:


> Hi,
> 
> I would like to use REW to tune my home theatre system and room acoustics, but i need some help understanding how to setup it up for best results.
> I have Marantz AV7702 MKII Preamp connected to EMOTIVA XPA5 GEN3 amplifier and focal 5.1 speakers system. i purchased UMIK 1 mic and miniDSP 2x4(for the subwoofers..2 SVS PB2000 coming soon:smile to use it with REW on my samsung laptop running window 10.
> ...


Many good questions.

Simple answer: With HDMI out and UMIk-1 in, no calibration is necessary or recommended. Or easy (or possible?).

Complex answer: loopback calibration for frequency and phase response is only meaningful in a closed-loop situation with an analog input and output in the loop, like with an audio interface with mic preamp, ADC, DAC, line level output. The analog output points you suggest are reasonable possibilities. But the only analog input is the mic capsule itself. There is no purely electronic way to do it. A closed loop allows you to correct for BOTH the input error AND the output error together. You never will know how much of that error is at the output and how much of it is at the input. You could only figure that out by introducing another reference into the system, like a calibrated audio voltmeter. Which is how they calibrate the UMIK-1 in the factory. So the point most prone to error, the mic input, has been calibrated for you in that manner.

The good news: With the grade of components you are using, if you can let go of the notion of NEEDING to calibrate, your measurements will be just fine. The extremes of the audio spectrum will be within a fraction of a dB. For that thunderous LF response you will undoubtedly be looking for, you will be looking at peaks and dips, not if the response is flat to 5 Hz (at 5 Hz, "flat" has no meaning anyway), &/or using a target curve, &/or making manual adjustments to taste, &/or something like that.

Sounds like you are good to go!


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## AVSION (Sep 11, 2016)

Thank you for clarifying that,

after setting up my system for level match speakers as described above, i'm getting high SPL readings when using REW.
i was following "Getting Started with REW: A Step-by-Step Guide (Rev 5.2 August 10, 2016)" and setup the system as follows: 

1. Prepare the AVR:
a. Using the AVR’s setup menu, adjust each speaker’s trim to zero as a starting point.
b. Set the AVR master volume to zero.
c. Disable output to the sub channel. This can be accomplished by turning off the sub(s), or by setting the speakers to “large”.
d. Set the AVR’s output to stereo.
e. If your AVR has automated room correction, make sure it is turned on (we want the speaker levels set with room correction engaged).
2. Select the calibrated USB microphone and the 90-degree calibration file that contains the sensitivity parameter. (If you don’t have the custom 90-degree calibration file, use the calibration file you have.)
3. Set up the mic at the MLP, pointed towards the ceiling, with the tip of the mic at ear-level.
4. Make sure the Windows audio input and output devices are configured properly as per the instructions earlier in this Guide.
5. Launch REW.
6. Open the REW SPL tool and click the red button so that the SPL is measuring sound levels.
7. In the REW preferences screen, select the HDMI channel for the first speaker you will be measuring (e.g. HDMI1 for the left speaker).
8. Open and configure the REW Signal Generator:
a. Select Pink Noise.
b. While measuring the main speakers, select “Speaker Cal”.
c. Set RMS Level dB FS to -30 (Why -30? See note below)going 
9. Click the Play button in the Signal Generator. You should now have a tone playing from the left speaker.
10. Observe the sound level being displayed in the REW SPL. Normally, it should be fairly close to 75dB (within +/- .5db).
11. In the AVR’s setup menu, go to the speaker level-setting screen and adjust the trim for the speaker upwards or downwards until you see a reading of 75dB in the REW SPL. (If the REW SPL meter is fluctuating too rapidly to set the level precisely, you can open the SPL Logger, which might allow a greater degree of precision).

when i get to step 10 it reads 90db SPL not 75db, this is 15db higher, although i followed all steps one by one, 

to double check the SPL levels i used another method by generating the build in pink noise in the AVP as the AVP or AVRs uses -20db pink noise, i set the MV down -10 db (from reference) to get 75db SPL and did get 75db SPL readings. 
any idea where this 15db in gain coming from? its driving me nuts :hissyfit: i would like to use REW manual process that is recommended after running auddyssy.

Also in step 11 they asking me to adjust the levels in the speaker level-setting screen, it is not possible as when you go in to the speaker level-setting screen it automatically run the build in pink noise and disable REW pink noise. i do have in option screen speaker levels settings, for fine tuning, where i can adjust with REW pink noise but the option screen levels solution does not link to auddyssy which is important when making changes. anyone knows how to run pink noise from REW and use speaker level-setting screen to make the changes?

I'm basically stuck at this point, appreciate your help

Thank you


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## AudiocRaver (Jun 6, 2012)

Correct me if I am missing something.

The system is a big loop, from REW generator to REW SPL Meter, and the level reference point for the entire loop is the sensitivity number in the mic's calibration file, so that is set (as it should be) and fixed. Your AVR's volume level and channel trim have been fixed in a completely arbitrary way. The speaker sensitivity is fixed. The generator level is arbitrarily set at -30 dBFS.

Your measured level is what it is. _Calibration_ means changing a gain somewhere in the loop so that a measured level somewhere in the loop matches a reference. I do not see that happening in your procedure. It seems like it would take place in your AVR. Use the -30 dBFS in the generator and trim the channel gain to give 75 dB at the REW SPL meter.


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