Stereo Mic Input Versus Line Input

Mic-In is always mono, but the software that manages it almost always puts that one sound on both left and right if you’re building a stereo show. It can seem like your show is in stereo, but it’s not. It’s in two-track mono.

The battery supplied on the ring connection is only 5 volts and it’s heavily buffered, so it shouldn’t do any damage if you plug the wrong thing in. You’re most likely to get into trouble with sound levels. The Mic-In is expecting a tiny, delicate, mono microphone signal and the Line-In is expecting a powerful, massive, stereo sound signal. Usually when you cross them, the show is heavily distorted and overloaded. The words crunchy, harsh, and crackly get used a lot. There is no way to rescue that show. Digital overload is immediately obvious and permanent.

If you did get clear sound, you have the celebrity sound card that doesn’t throw up if you cross the cables. Most sound cards will not do that, and yes, you do have to get the right connector to do the job.

Some sound cards can switch between Mono Mic-In and Stereo Line-In in software. These sound cards do not have two connectors.


That’s correct. There is usually a 5v supply on one of the contacts. The current should be limited to no more than a couple of milliamp so it is unlikely to do damage but it’s safest to avoid plugging other types of devices in there.

Other than the microphone input has an option of 20dB boost and the 5v supply there may be no difference. Exactly how manufacturers implement microphone inputs is their design decision, but it’s usually based on (low) cost rather than any performance considerations.

On high quality music sound cards it’s a different story and there will be considerable differences between Mic and Line inputs. On these you should definitely avoid putting a high level signal into the mic input. The microphone input will be a balanced 600 Ohm input with high gain circuitry, whereas the Line input will be a low gain input, usually unbalanced, with an input impedance of around 20k Ohms.

Thank you for your response, Koz.

Although both my front and back “mic” inputs are labeled as such (microphone), they do take a stereo input. As I explained, I plugged the headphone port of my sound card into both mic ports in sequence and recorded the output: what I didn’t make clear enough, perhaps, is that I was playing a tune that begins with an overt left-to-right pan of a vocal sample, and the recording to the “mic” input reflected this pan appropriately across the left and right channels that it was recording.

At first, I thought for sure that forcing Audacity to record stereo from the mic port would only result in my mono microphone’s output being mirrored across both channels (the way that it used to on my old laptop). When this turned out to not be the case (the left channel got no signal), I plugged in the mentioned stereo output (headphones-out), and, sure enough, the mic records in stereo.

Thank you for the warning regarding the levels, but I did anticipate that problem by lowering the levels accordingly (disabling the mic-boost entirely and adjusting the capture amplification). Like I said, the recording that Audacity captured was very identical to the same thing recorded via line-in.

Stevethefiddle, you’ve posted while I was typing this response, haha. Thank you for your response as well; it’s very enlightening.

Both of you have said that the power sent back through the mic port is probably not enough to cause any damage, but that it should probably be avoided, and so I will avoid it – after all, I do have a line-in port as well. It just seems weird that these microphone ports would record in stereo… I’ve heard of stereo microphones, but I assumed that those would be recorded over line-in for that reason. Hm.

Thanks again.


The two services have been hopelessly scrambled by the different manufacturers most of whom want desperately for the difference to just go away. Many posters begin their question with: “I plugged my mixer into my computer Mic Line-In.”

I bet that if you plugged a “real” computer microphone into your mic-in connector, it wouldn’t work. Further, I bet there is no 5v battery on the ring connector.

I didn’t write about this, but the difference between commercial microphone level and line level hovers around a thousand to one. Scaling up to a silly analogy, that’s the difference between the shiny glass High Tension power lines above the trees feeding your whole neighborhood and a flashlight battery. 1.5 volts versus 1500 volts. Not easy to get both of those on one wire without damaging something.

Microphone manufacturers have been pushing higher and higher sound levels and conveniently hiding the sound quality which always suffers when they do that. I would kill to have the 20dB Microphone Boost on all our sound cards. That’s the only way some of our training and demonstration equipment works.

I only talked about the high volume and overload end of the problem. The other end of things is in trouble, too. If you plug a “real” microphone in, chances are the volume level of the microphone and the noise level of the sound card will be the same thing. “Microphone Test ffffffffffffffffffff Hello, testing ffffffffffffffff.”

You can actually recover a little bit from that, so that’s not as bad as overload which is permanently fatal, but you can’t get a quality show from either one.

Not easy this microphone thing.


Stereo mics (usually) use mic level inputs just the same as ordinary mono microphones. They will often use the same kind of mini-jack as an ordinary mono computer microphone (with tip, ring and sleeve connections). Whereas a normal mono computer microphone uses the tip and the sleeve for the microphone and the ring for the 5v, the stereo mics use the ring for both one of the mics (there are 2 microphones in a stereo mic) and also for the 5v.

It is highly unusual that a computer microphone input works in stereo (these sort of microphones are usually used with portable recorders, pocket video cameras and suchlike). It may be interesting to try and plug a cheap stereo microphone with your sound card and see if it will actually record in stereo from it. A friend recently bought a cheap Chinese copy of a Sony stereo mic from ebay for the equivalent of about $5 (including postage). At that price it may be worth testing just for the fun of it.
The microphone he bought was certainly not up to the standard of a real Sony microphone, either in build quality or sound, but for $5 the sound is surprising not terrible (though the build quality is extremely flimsy). These microphones are very readily available - if you’re interested, look up “ECM-DS70P”

Ha ha, that’s just what my laptop microphone sounds like :smiley:


Thanks again for the information. I use an ElectroVoice stage microphone for my PC mic; it’s a pretty nice, classical (dare I say, “real”) microphone, and it works fine with my microphone ports. That being said, yes, the amplitude of the output is extremely low as should be expected from an unamplified mic, but the sound-card’s microphone boost (which can be turned off or set to three different increments of amplification) brings the amplitude up to even clipping levels if the general capture volume is maxed out along with the boost. My only complaint about the inputs on this sound-card is that they’ve all got a bit of an offset that becomes increasingly obvious as the signal is amplified, but it’s very manageable, and I can’t expect an integrated sound-card to be perfect, I suppose. The background noise on the front mic is practically non-existent, although it is noticeable on the back mic – nothing that I’d be particularly ashamed to record over, though. I do wonder if the ports are powered at all, as many mic ports apparently are… I mean, if they weren’t, they’d essentially just be line-in but with some extra, optional boost, seems like.


Thank you for describing the anatomy of a mini-plug; I see that I’ve had it all wrong all of these years. I’m no expert with audio gear (obviously), but I’ve always noticed that mono plugs have one ring and stereo plugs have two. As such, I sort of always imagined that the actual tip and sleeve of the plug did nothing, really, but rather the output signal was read through the rings – thus, one ring for mono and two for stereo. So, despite outputting stereo, stereo mics still only have one ring? Also, if a mono signal is actually sent through the tip and sleeve of the plug and the ring is for power, what is the second ring for on stereo (line) plugs?

I can’t believe that I’ve had it so wrong… I mean, before today, I never would have even imagined that power would be sent FROM an input port and BACK through an audio cable to the attached device…


Just to be confusing, some stereo mics have 2 rings, in which case it’s tip + one ring for signal, 2nd ring for 5v, sleeve for common (earth).
Some stereo mics have just one ring as seen here (and the arrangement is as described previously):

Computer microphones invariably have one ring. Tip=signal, ring=5v, sleeve=common.

That’s why they call it “phantom” power (it’s invisible). Computer microphones are usually a cheap form of “Condenser” microphone (technically called an “electret” microphone). They include a tiny amplifier which needs to be powered, hence the 5v. True condenser microphones require more voltage, typically 48v which is usually supplied in a similar manner - by sending the (phantom) voltage up the microphone cable.


I’ve always been aware that USB cords can both transmit data and send power back to the device, but I didn’t know that microphone ports have batteries and that audio cords could work in a similar way. Wild.

So, again, what is the second ring on a stereo plug for? Maybe I should just look it up on Wikipedia… or maybe one of the rings is still for power, just in case. I mean, I guess there’s no reason why I couldn’t use one of my “line cables” to hook up a mic. So, maybe… it’s the tip for one signal, the first ring for power, and the second ring for the second signal. But, then again, you said that, on some stereo mics, the second ring is for power, and so standard ports would probably have to support that, too. So, maybe… it can take a signal and send power on both rings? Man…

Yeah, I’m gonna look it up, haha.


EDIT: Learning a lot about the subject on Wikipedia. I don’t mean to sound like a total novice, and please don’t waste any more of your time answering my silly questions when I’m sure that there are plenty of excellent resources for this sort of thing online. Thank you for all of your help.

EDIT: By the way, if I sound like I have no idea what I’m talking about in some of my sentences in previous posts, it’s because I’ve actually been referring to the black, insulated rings as the “rings.” I honestly thought that this is where the conduction happened, despite the fact that the rest of the plug is the shiny, metallic… yeah. So, I’ve never used a “computer microphone,” but I guess that I would have been confused by it because its tip would have looked like what I typically understand to be a “stereo” plug. This is because, unlike my stage mic, the plug has two black, insulated rings, which split the plug into three conductors: the tip for the output signal, the middle ring for power, and the rest of the plug (sleeve) for ground. As such, computer mic ports would have to be prepared for three-conductor plugs, just like line-in ports, although they’d handle these plugs differently. Apparently, MY mic ports must be able to use the ring for power and/or as another input signal, meaning that they can record in stereo, so, aside from sending power (can line-in ports typically do this?) and having a dedicated mic amplifier, they’re no different from line-in: after all, if I plugged my mic into a line-in and amplified it to a huge extent, I could record from it.

I’m still a bit weirded out by the prospect that my mic ports MUST be able to send phantom power in order to be compatible with typical computer microphones, but they can also use that middle ring to record from, apparently.

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…

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.


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.

(scroll down)


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.


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.

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.


following on from koz…

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

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.


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…


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 ( 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?

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

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.

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.

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…

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.


Hello everyone! I now better understand the line input versus the mic input on my czh-05B FM transmitter. Using a computer microphone I cannot obtain any signal. My line input transmits perfectly. I am thinking that perhaps when I attempted to input a line signal into the mic input socket, I may have overloaded the mic input circuit??? Any thoughts as to this possibility being my reality? I have ordered another FM transmitter (same model) so I will attempt to use the mic input for only a microphone when it arrives and see if it will transmit voice. Thanks for all the information…it has really expanded my understanding. Rob