Originally Posted by JimP
Originally Posted by Stealth3si
regarding post #10, If the usb mic already comes calibrated then why calibrate it (again) with a spl meter?
if someone doesn't have a usb mic and spl meter isn't better to get dayton audio emm-6 and a usb dual art pre?
I'd think that the intent is to be sure that you've go the mic set for the correct sensitivity which varies depending on your computer hardware settings.
Should only take a few seconds to perform.
Correct. Your input gain settings and the sensitivity will affect the results, so the first step to getting accurate results is to verify that the readings from the Mic correspond to the readings from a known device (an SPL meter). The calibrated mic is merely calibrated to generae a correction file for the deviation from a flat response, compared to a known accurate device. If a particular mic reads 90db at 200Hz where the Reference mic reads the same, but only 75db at 20Hz where the Reference Mic reads 85db, then the correction file reintroduces that 10db difference to the output measured at that frequency with the calibrated mic so the results are in line with what you'd see if you were using a Reference spec mic. To sync everything up though, you need to first verify that a tone with a 90db SPL is being measured by the system in total (with Input Gain settings, avr output volume settings etc.) AS 90db.
Although this next bit is stepping a little ahead of the current position in using REW, when and if you ever choose to try system distortion limit measurements, you'll find that you'll need to bring out the SPL meter again and tweak the Inut gain settings.
Eg. when I tested my setup to see if it could indeed play flat to 105db SPL at my MLP through 20Hz-20kHz, I measured the FR at 75db, 85db, 95db and 105db then compared the graphs to see if there was any deviation in the Frequency Response measurements at increasing SPLs to see if compression or clipping was beginning to rear its ugly head. You can't just simply turn up the volume knob on the avr and take measurements at the louder volumes though. That 30db difference between the first set of measurements and the last was too great for the measurement system and would clip the inputs if I didn't turn the measurement setup's input gain down. That's one of the steps in REW, you verify that the REW measured SPL with your mic of choice corresponds to the SPL read by a known device (like a RatShack SPL meter), AND set up the Input Gain so you have an optimal range for the measured signal. Turn the Input gain too high and you'll clip the input signal, rendering the measurements useless. Set the Input gain too low and you'll be obscuring data (BTW, this was with my external Roland Quad Capture soundcard with it's own Gain knobs etc. PLUS the Input and Output gain settings in Windows and REW, so your mileage may vary if you're solely using the internal soundcard with an USB mic).
No, REW is NOT Plug N Play in the manner most folks have come to view PnP. Definitely not in the way that Omnimic or XTZ is, but that said, I do feel that it IS worth the effort for me to use, as it has tools that the other systems don't, and the USB mic plus HDMI connection setup will make things a lot easier to use,... once you have all the basic settings ironed out, and unfortunately, that's where one of REW's steep learning curves comes in. All the little settings in Windows (and the various different versions of Windows that different users may be on) that need to be correctly set for everything to work together. No sound from HDMI? Did you set your soundcard's outputs correctly? My laptop doesn't automatically output sound through the HDMI connection, only video. I have to go into the configuration to change that manually. Once I know how and where to do that, it's quick and simple, but until and unless I know that, it can be a PITA. Did I configure the input channel settings in Windows correctly for REW? (this was my first PITA when trying to hook up my external soundcard. Took a while for me to figure that one out).
HDMI plus USB Mic Plug-N-Play? Definitely not for a newbie. A lot easier once you figure out all the proper configuration settings? Yes, definitely. More powerful than OM and XTZ? Yes. Worth the hassle and frustration? Yes to me, but up to each individual to decide.
MaxEdited by djbluemax1 - 1/10/13 at 2:03am