Is This Normal?

[borntoplease]

Is This Normal? Testing Mic Pairs...

so i decided to test out my new mics to see if they sounded the same. they ARENT a matched pair... so. they are earthworks SR71s... sound treated my room and got it sounding pretty good (if anyone saw my other thread about recording my guitar you know what im talking about...) anyway... i got the idea to see how close in sound they were... and now im a little dissapointed. i figured that even though they werent "pairs", because they were from earthworks, a very reputable company, they would sound somewhat similar. i tested on my vocals and my acoustic guitar. i set the mics side by side, as i identical as i could possibly get them. well, they dont sound similar. one is noticably lounder than the other, and as a result has a little bit more clarity. now i thought this could by my preamps... but they are on exactly the same notch, as far as i can tell. i am just using the pres in my digi 002 rack. whats up? these are used mics and in great looking condition. doesnt look like they've been abused at all. but for some reason they just dont sound good. is this normal for an unmatched pair? the other mic doesnt sound bad, at least not to my untrained ears, just a little less loud. i mean, when i recorded and looked at my wave forms, the peaks look nothing the same. you can tell its the same source, but it sure doesnt look like the same mic. is this normal? can mics be repaired if there is something wrong? where would i take/send them? any advice will help. im feeling a little frustrated. i just spent 100 bucks to get my room sounding decent, now i realize my mics arent sounding good... aaaahhhh!!!

 

[baekgaard]

If they are not a matched pair, there is no guarantee that they will match in polar pattern, frequency response and levels -- even when from a reputable source.

But if the polar pattern and frequency responses are roughly equal, you're OK even if the levels are not.

Here is how to test them properly:

* Align them as closely as possible. Capsules should be in the same plane, next to each other.

* Invert the phase on one of the mics (on the inputs of your mixer, or by a mic cable were one of the ends have had the hot wires swapped). Press the mono button on your mixer, and listen with headphones. Using the pan pots is not good enough, as they may not perfectly put the image in the center.

* Start talking to the mics, from the front at maybe 15" away, while bringing one mic to a "reasonable" level.

* Bring up the other mic until your voice cancels out. It will usually not cancel out fully, but you should be able to get close to cancelling out.

* As the mics are not having the exact same sensitivity, they will not be exactly equal on the preamp/faders. This is OK, and you should not worry about this.

* Listen carefully to how they cancel out one another. Are there certain frequencies that are gone, and others that are more prominent? If so, the frequency response may not be identical. You may have to raise the headphone levels to hear this, but be careful not to blow out your ears ;-)

* Now walk around the mics, speaking (or easier -- having someone else speaking) to the mics. If there are any angles at which the signal becomes stronger, the polar patterns are not well aligned. Some variation will be expected, but not a lot. Don't get too close to the mics while doing this, as proximity effects will be giving wrong results.

Ideally this will work well with perfectly aligned mics in a non-reveberant room. In practice, there will be small deviations -- but you may not need to worry about it.

This way, you can check their patterns and frequency response.


Now, the other issue is of course whether it is a problem in real life or not.

For a guitar recording, mics does not have to be perfectly matched. If they are not, there may be a slightly instable stereo picture (i.e. certain frequencies sounds as they come from a different place than others) even when using a well-aligned XY configuration. But if you have a spaced pair setup, this will probably impact the stereo image more than having a slight difference in the mics.

For guitar, you can sometimes even get away with using different mics.

Only if you do a true stereo recording of e.g. an orchestra will you need well matched pairs. But even there, you may get away with slight imperfections.


So... try the above, and hopefully you'll find that all is well! The test you already did is not realiable.


-- Per.

 

[borntoplease]

wow... thanks for all that info. i'll try it as soon as i have some time. i hope all turns out well...

thanks again.

 

[borntoplease]

update, i tried the this technique. this is what i did.

i got the mics on as close a plane i could. my mic stands were being dificult so there may have been a couple centimeters difference, but just a fraction. i pulled off about 15 inches and spoke into the mics. my room was dead, 95% of all the room sound taken out with sound treatment. i wasnt sure exactly how to invert the phase. i have pro tools, and unlike most boards, there isnt a phase button on the strip. i put a delay plugin on, turned off all the delay and stuff, and hit the phase button. i hope this worked. i dont know how to put it into mono, but i assume with a daw, if the pan is in the middle, it really is in the middle.

i recorded myself speaking into the mics at a normal voice level, i moved over to both sides and spoke again. then i went back to the computer and moved up the out of phase track. i figurered they would cancel themselves out near unity, but i had to push the out of phase track up higher. there was near cancelation at +2.7dB. it sounded like the very top end came through faintly. i could still barely make it out in my headphones, but it cancelled itself out about 96% i would say. when i moved to the sides nothing came through any more, if anything, it got quieter, but that may have been because the mic was cardiod and was just not picking up as well.

i hope this means they are somewhat close. there was still a slight volume difference, but i suppose thats not a huge deal.

if anyone can give me any more tips on testing the mics that would be cool. i hope i dont have to shell out more money for another set of mics.

but then again, new gear is always fun... but not having any money isnt.

like if full of hard choices.

 

[mshilarious]

there was near cancelation at +2.7dB.

That's at the upper range of typical variation, but probably still within spec. Figure that the sensitivity is about +-1.5 to 2dB.

 

[baekgaard]

i hope this means they are somewhat close. there was still a slight volume difference, but i suppose thats not a huge deal.

You should be able to do just fine with this pair of mics then. Mark the phone which is less sensitive, and give it the +2.7dB boost, and you'll be able to get a stable stereo recording with this.

So, no need to worry any longer 'bout this -- now go make some music; spending time finding a good placement of the mics with your guitar instead is going to have a much larger impact on the overall sound.

Good luck


-- Per.

 

[borntoplease]

good to hear then... im glad, i can sleep now, i've been up all night worrying i just threw away money...