Topic: Matching

[Big Muff]

I've got 6 nakamichi cm-700's..
I'd like to get a pair matched as closely as possible.  How is this done?

cheers!

[John Willett]

I've got 6 nakamichi cm-700's..
I'd like to get a pair matched as closely as possible.  How is this done?

cheers!

Are they supplied with individual frequency response curves?

If so - hold them up to the light one over the other (so you can see both curves) - repeat until you find the two that most closely match.

This was the way they did it in the old days.

Otherwise it will be expensive as you will have to send all six mics away to someone who can measure them properly in an anechoic chamber to get the curves - this will cost several hundred pounds (Euros, Dollars, etc.)

[Gutbucket]

If sending them somewhere to be measured is too costly, you can so your own matching.  It won't be as close as a match made in a proper facility, and you won't end up with an acurate response graph for each mic, but all it takes is your time, careful methodology and gear you probably already have.

The simplest type of matching compares the mic output levels for a given input.  Play a 1Khz sine though a speaker, record that output though each mic one at a time- be very careful to position each mic in exacly the same location and orientation when under test and also careful to not change the playback or recording levels.  A good check to make sure you have things arranged close enough is to re-run the test group a second time, checking to make sure that the results for each individual mic are the same.  Then analyze the recordings and check the RMS levels for each file.  Pair up the mics with output levels that are closest to each other.

Matching for spectum is probably more important than matching for level though, because level differences are easy to adjust during or after recording.  To do so simply, set up the same test situation as above and record some pink noise instead of a sine signal (you might run both these tests one after the other to keep from having to move mics and set things up twice).  Listen to the recordings and choose mic pairs from those where the recorded pink noise sounds closest in timbre.  In this case you are making a subjective listening comparison between mics.

You can make your timbre matching more accurate by running the resulting pink noise recordings though an audio analyzer plugin which averages the output of the file over the lenght of the file and displays an average reponse curve.  Save each curve (or even an image of the curve) and compare the responses.  You can do it the old fashioned paper way and print them out, line them up and hold them to the light like John mentions if you like.  The resulting curves will not be very accurate representations of the actual response of the microphone like as you would get from a professional response measurement using calibrated test equipment, but that's not important here.  What is important isn't the shape of the curve from each mic, but the differences between the curves of the mics.  Pair the mics with curves that match most closely.

[Chuck]

I use a method this very close to the one Gutbucket posted. But, I will add that I like to position the microphones 4 feet or more from one full range speaker. I use a tape measure to get the mics the same distance away. I always do it all in one day, with one set-up, because even a little change in position can make a big difference.

I also listen to the pink noise results. I import all the mono files into CuBase and line them all up on separate lines. Then I can easily loop the pink noise tracks and switch between them to listen for differences between the tracks. I made a test CD that has 10 seconds of 1k sine WAV followed by 1 minute of pink noise, so I can swap out mics quickly. I just hit the play button on my CD remote and I can get it all done fairly efficiently.