# USB Microphones for RTA



## Foglght

I was hoping to hook up my laptop and do some RTA finally at my home. I spoke with Geo about getting a mic, but he said that I needed a pre-amp. 

Is there a way to use a USB mic and just get the software?


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## npdang

If you have a soundcard with a mic input that will power a mic, then you're ok. I've never heard of a usb mic though.


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## Foglght

http://www.audiojunkies.com/blog/927/xtz-room-analyzer

Would something like this work?


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## OBXTINTWORX

I'm Trying to do the same thing. I found the software. Freeware.

jDFT - the free RTA software for Windows

now for the mic. Most true RTA microphones are condenser mics, meaning
that they need power to them which is usually supplied through the XLR
connector from the pre-amp. There are usb mics for recording but most of them
seem to loose frequency response above 15k. The next issue is how flat the frequency response is. Mic's are selected for different insrtuments based on how they naturally roll off certain frequencies. DBX makes a great RTA mic if
we can figure out how to get the "PHANTOM POWER" to it.

Still Searching..


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## OBXTINTWORX

Getting a little pricey but this will work.

Here is the adapter that will provide the "Phantom Power" to the mic.

Buy Shure X2u XLR-to-USB Microphone Adapter | USB Microphones | Microphone Accessories | Musician's Friend

And here is the only mic i could find with a "Flat" frequency response.

Buy dbx RTA-M Reference Microphone for DriveRack PA | Condenser Microphones | Signal Routing | Musician's Friend

But this set up should be pretty accurate.


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## ErinH

^

http://www.diymobileaudio.com/forum/diyma-tutorials/38290-how-make-your-rta-100-dlls.html

that should help.


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## lilmike

There are a lot of mic options out there, some of the best are really cheap.

I used to get by with this sort of a setup:

Simple DIY Microphone

The capsule is essentially flat from <20 Hz. to >20KHz, so it is certainly not the weak link. Laptop sound cards are not the best, mine have typically had pretty poor frequency response and really high background noise.

Buy the capsules here (yes, they really are under 2 bucks, but Digikey has a minimum order charge IIRC):

Digi-Key - P9925-ND (Panasonic - ECG - WM-61A)

With a soldering iron and some wires and stuff you probably already have laying around, this will work fine with the mic input of a typical laptop. Buy more than one capsule - they are TINY, and can be a bit tricky to work with.

For me - it worked pretty good all around and did fine with RTA, but the Laptop soundcard rolled off badly below 50 Hz and above 14,000 Hz. I really needed more accurate bass response for testing my subs.

In my case - better response required a better sound card, which meant I needed a mic preamp too. I use the Emu 0202 USB external sound card and a modified Radio Shack SPL meter as a Mic and preamp. Modifications are detailed here:

Eric Wallin's Internet Homepage

I'm no electrical engineer, but I do know which end of the soldering iron to hold. I was able to do all of the modifications as described in under 2 hours, and the meter worked perfectly afterwards. 

A lot of very good software is available for free, spend your money on measurement hardware. Google is your friend here.

Not counting the Laptop, I think I have less than $125 in my whole SPL/RTA measurement setup, including the Emu-0202 which was $80. With this setup, I'm limited to measuring SPL's I actually listen at (there are some issues above 125 dB with the capsule), but that has not been a problem. Also - it is not SPL calibrated, but as I typically worry about relative changes in SPL, that is not really an issue for me either. 

Need more info - drop me a note.


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## donkeypunch22

just as bikinpunk said:

http://www.diymobileaudio.com/forum/diyma-tutorials/38290-how-make-your-rta-100-dlls.html


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