Stereo Mic Input Versus Line Input

[kozikowski]

Officially the three contacts are Tip Ring Sleeve. I've seen them called TRS connectors, but that's not at all common.

This really is how they're wired...

http://www.kozco.com/tech/audioconnecto ... ctors.html

You can have special purpose connectors with multiple rings, but those are not at all common and therefore are more expensive. You may have something like that to mate an advanced microphone with a special sound card.

Koz

[kozikowski]

Condenser microphones all work roughly the same way. Two thin metal plates whose separation changes with the pressure of your voice. They all need battery of some sort because the raw sound signal these plates make will not go down a cable. The internal condenser amplifier doesn't necessarily make the signal any louder, but it does make it a lot beefier so it survives the cable run.

You can see the metal plates on a larger condenser microphone. That's the inch-wide round disk behind the grillwork.

http://www.recordingreview.com/articles ... Page1.html

(scroll down)

Koz

[vencabot]

Thanks for all of the information, Koz. I actually spent all day yesterday learning about mics and connectors, and I feel a lot more confident with my terminology, but my lack of elementary electronics comprehension keeps me from completely understanding where all of the voltages are running in my adapter-heavy set-up. My microphone is dynamic, balanced (XLR), and doesn't require phantom power. The cord that I use for it is female XLR at the top and a 1/4", 2-contact TRS (that is, just a tip and a sleeve) at the bottom. In that case, I don't see how it's balanced anymore, unless the signals are combined before they reach the TRS.

Since the mic jacks on my sound card are 1/8", I use a 1/4" to 1/8" TRS adapter, but it's actually 3-contact to 3-contact (stereo to stereo). It does the job, but it makes me wonder if my mic is receiving phantom power at all or what. For simplicity's sake, I'm thinking of buying a 2-contact to 2-contact adapter soon, since that more properly reflects what I need in this situation. Alternatively, I could get another cord so that I can take full advantage of the balanced output -- one that ends with a 3-contact TRS instead of a 2-contact one.

I still have no idea what I'm talking about, but I do feel more initiated, at least, and that'll make the rest of my research easier.

-David

[kozikowski]

Grown-up microphones, the ones with the 3-pin XLR connector, do not use ground for the performance signal. There is a ground or shield connection there to keep interference and electrical buzz out of the show, but it's not part of the show signal. Copper land line telephones work this way and they don't have a shield at all.

The shield/ground is almost always pin 1. The show is entirely balanced between the other two pins, 2 and 3.

Computer microphones don't work like that. They send the show down one wire only and use the shield or ground for the other. To get between the two systems, you have to unbalance the professional microphone -- force pin 3 to be ground.

This diagram has the formula to do that.

http://kozco.com/tech/audacity/UnbalBalAdapter.jpg

If you do have an adapter that goes from XLR to Tip, Ring, Sleeve, chances are terrific that pins 2 and 3 are wired up to tip and ring. I have a simple sound mixer that works like this straight from the store.

If you're still following this, that means some of the show signal is connected to the computer battery if you plug this into a sound card Mic-In. That can put computer battery into the microphone that wasn't expecting it. This is where you can create some damage by plugging things in where they shouldn't be.

Koz

[steve]

following on from koz.....

.... so the best option is a sound card that has an XLR socket.

[vencabot]

Thank you, Koz. That answered my question. From what I read, phantom power will not damage modern dynamic mics, although it can be very dangerous for ribbon mics and older models of microphone. I may very well pick up a new cord for my mic knowing this: one that's XLR at the top and 3-contact 1/4" at the bottom rather than a 2-contact 1/4". I may not, though, since I don't really need balanced input for my amateur-ass recordings.

Have a good night.

-David

[kozikowski]

Or what most people do is give up on the noisy computer sound services and invest in a quiet, well behaved external USB sound card...

http://forum.audacityteam.org/viewtopic.php?f=27&t=9477

Koz

[ditzel]

I need some help, and this topic is somewhat related. I have a Canon Vixia HFS100. I'm recording some medical educational videos for a website I'm creating (radiologyforpatients.com). I have a Shure wireless lavalier set up that I'm wearing. I bought an XLR to 3.5 mm adapter cable (by Hosa) for about $8 to connect the wireless base station to the camcorder. I did my recordings and they sound ok - better than the built in camcorder mic and even better than Canon's shotgun mic, but they recorded only mono. Stereo isn't essential for my use in this case, but it would be nice. Any ideas what's going on?

[steve]

I have a Shure wireless lavalier

That's a mono microphone, so it can only record mono.

[kozikowski]

Most "computer" microphones depend on this 5 volt battery being supplied by the computer. If you buy an analog headset with earpieces and a microphone on a boom it will almost certainly need that battery connection from the illustration.

http://www.bestbuy.com/site/Plantronics ... Id=9210276

One plug is for the stereo headphones and the other is for the microphone. You need to pay attention to the colours because the electrical plugs are exactly the same.

If you have two microphone inputs, then you have an electronic celebrity. All "usual" bets are off. It's most unusual for a sound card to have two microphone inputs -- unless it's external.

All that and there's another variation. Radio Shack makes a very nice "tie tack" microphone that doesn't use the computer battery. It has its own little battery in the switch module.

http://www.radioshack.com/product/index ... Id=2102927

And don't confuse the two phantom powers. The 5 volt one isn't so phantom because there's actually a wire in the cable that's carrying the battery up to the microphone to run it.

The recording studio phantom power goes on a connector like this...

http://en.wikipedia.org/wiki/XLR_connector

That one is borderline magic because the 48 volt battery goes up to the microphone and the sound comes back down on the same wires.

Koz