Sunday, January 22, 2012

Step-by-Step setup guide to Room EQ Wizard (REW)

If you're like me you were overwhelmed by the REW "guide" on home theater shack. So here is a more thorough step-by-step of how to get REW working. I like to think once you have everything hooked up this guide will get you measuring in about 10-20 minutes.

First things first lets go over the equipment needed

    Notes about Equipment
    The cheapest good audio interface for the purpose of measuring is the tascam US122 MK2.

    It has decent DACs as well and functions as a decent 2 channel device.

    I have studio monitors on my desk setup and if i were to do it again i would buy an m-audio mobilepre audio interface because it has balanced outputs. The tascam's knobs also feel a bit cheap and the m-audio might feel better built.

    For those wanting cheaper, i dont know of anything. If you have a capable pci soundcard you can skip the tascam and buy a behringer xenyx 502 for phantom power (to power the emm-6) but it gets a lot more complicated AND it's not portable. So i would recommend buying an actual audio interface like the m-audio or tascam that has phantom power built in.

    (Note: for this guide I'm using my tascam US144 MK2, thats why it looks slightly different)

    SPL meter
    I have the aperion meter and I'm pretty sure its the same as the radioshack meter, it's just $29 with free shipping, making it a GREAT deal. For some reason it's still a fairly well kept secret. It's pretty accurate too which cant be said for a lot of the cheaper mics on places like amazon

    Issues with
    Some of you are probably wondering why I've recommended cheap looking cables when monoprice has "nice" ones for cheap. The problem with monoprice is they had a bad batch of RCA->XLR cables over the course of several months. I ordered cables in november, RMA'ed them almost a month later, then they shipped me even more defective cables. I dont trust them to wire RCA->XLR cables anymore, so i can't recommend them. The "cheaper" looking cables work for me fine. Youre free to order from monoprice, just realize if you dont have a multimeter and know the pin guide its hard to establish if a cable is broken or something else is.

    The Dayton emm-6 comes with a calibration .txt file (this will makes sense later in the guide) from 20hz to 20khz, if you think you have a serious subwoofer setup and have a lot of output below 20hz you may want to buy a mic that is calibrated from cross spectrum labs. The Basic+ is $75 + $9 shipping. This will result in 5hz to 20khz calibration. Apparently its also recommended for car audio measurments (probably because it offers 90 degree angle of incidences if youre facing the mic "up" at the position of your head in a car, best guess).

    Alright, now onto the instructions:

    Before opening up REW make sure your windows levels are up all the way on the tascam (if its not shown, right click on the volume icon and go to "Volume control options" to enable it)

    Once REW is open click on preferences

    Time to configure the inputs/outputs.

    This guide uses V5.07 beta. v5.07 uses "ASIO." Doesnt change much I just recommend using it, in the program you can change the output on the tascam from left to right in case you want to test two different subs without unplugging and plugging the cable. Make it look like the image below

    Tascams and most audio interfaces in the $100+ price range measure very flat from the factory, so you could get by without calibrating it all! If you are curious or still want to do it, please click HERE to read my page on calibrating a soundcard/audio interface in REW

    Now go to the mic/meter tab


    Go to dayton audio for your calibration file, input your serial number that is on your dayton emm-6, and save the .txt mic calibration file on your computer

    Now press on browse and navigate to the file, then press okay.

    Exit out of preferences...

    Now take your tascam, unplug the TRS to TRS cable, and plug in an RCA cable from the left LINE OUT and plug one end into whatever channel of your receive that you want to start measuring. If youre measuring a subwoofer you can plug it directly into the amp if you want. Turn PHANTOM to On.

    Plug your xlr cable into the tascams MIC IN L, and plug the other end into the emm-6

    For the purpose of measuring a subwoofer i put the mic facing down at the listening position at my couch.

    Before we can do frequency response sweeps time to take out an SPL meter

    Make sure the SPL meter is set to C weighted, and Slow response (highlighted below)

    Now, if you ran the built in calibration on your receiver then the volume at "0" should be reference at listening position. Basically means 85db where your mic is. Feel free to turn the receiver to "0" then adjust the LINE OUT on the tascam accordingly. Getting the SPL # accurate isn't extremely important if all youre doing is getting an idea of how your room behaves with low frequencies, as nulls and peaks will show up anyways. The program will still work exactly the same, its SPL numbers will just be completely off.

    Back to REW, press the SPL button

    Press "Calibrate"

    Depending on what youre doing select subwoofer cal or speaker cal, for our purposes we're doing subwoofer right now 

    If your receiver is on the right input and REW is configured correctly you should have white noise blasting out of the subwoofer. You might want to keep the receiver volume low so that way you can turn it up with the remote to a "comfortable" level while you hold the spl meter near the mic. Aim for around 85db, take it louder if you want just realize depending on how big the room is and what type of subwoofer that even 85db can strain it.

    Enter the number on the spl meter into the window, press ok, and close the SPL meter. Now its time to click on the Measure icon

    Change the start freq and end freq to 20 to 125hz, for most people that should cover the entire range of bass that can be "fixed," feel free to start the freq earlier if you know what you're doing. Set sweeps to 2 or 4 because it finds anomalies in the signal (truck driving by vibrating the floor, vent turning on or off, etc) and eliminates them.

    I dont know enough about the other feature of REW to write a guide about them, red spade audio does a pretty good job though here and the rest of the blog is very useful as well


    1. Excellent article and thanks for illustrating with photographs. It really cleared a lot.
      I have following questions.
      1. I ordered xlr to rca cable few days back after reading the article. What is the role of this cable? You mentioned to unplug it and I did not find the mentioning of connection part.
      2. I did not order TRS cable. I have TASCAM 144. Is it possible to use xlr to rca cable or RCA cable to connect digital outputs to digital inputs for calibration purpose.
      3.You mentioned to increase volume all the way up. The speaker icon for mine shows internal speaker but not TASCAM as illustrated. I don't know why. I connected TASCAM and also modified sound card preferences though.
      Appreciate your help. Thanks again for providing step-by-step instructions.

    2. 1. xlr to rca takes places of TRS to TRS. during the tascam calibration go from left line out (top of the tascam), to the left MIC IN. Its a slightly inferior way of calibrating the card, but is pretty close. This is how i calibrated initially, but i recommend TRS -> TRS now, if you have the chance pick one up for $5 from amazon sometime
      2. see above
      3. Right click the volume icon in windows and go to "volume control options" check the box next to "TASCAM US Speakers" and it should show up

    3. Thanks for clearing up all the questions. I already ordered xlr to rca and it is on the way. Next time, I will order TRS to TRS cable as well.

    4. Thanks for putting this together.

    5. Many thanks! Got this all ordered and ready to test when my new amp rolls in :)

    6. Thanks for the great writeup! I have been trying to get off the ground with REW but this newbie is baffled by the guide. One question--I was under the impression that the SPL meter with a line out could replace the need for the separate mic; I purchased the Galaxy cm140 because it allegedly had more accurate sensitivity in the upper range.

      I would like to take measurements throughout the range, for my main speakers and my new giant LLT/EBS sub (i.e. tuned to 13 hz). Am I still missing an adequate microphone? Thanks again for the great help this write-up is!

    7. Thanks for the guide, Appreciate your help. Thanks again for providing step-by-step instructions.

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