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I have a mixer that has 4 microphone channels. Each one has both a 1/4" jack input, and a three pronged input (XLR). I can choose one or the other for connecting my microphone.

I am about to buy cords for my microphones, and I wondered if there was any particular reason to believe that one type of input was any better or worse than the other?

(Please also note, I am not an audio engineer or experienced in audio production, so an answer with facts about "ohms" or "impedance" or other technical terms will go over my head. Please provide that information if you feel others may find it helpful, but I'm personally hoping for an answer in terms of results that a layman like me can use when choosing to purchase cables. Thanks for your understanding.)

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up vote 9 down vote accepted

The 3-pin XLR connector has two advantages over a 1/4" connector.

  1. It provides balanced audio, which means that the cable is protected against electrical interferences from mobile phones or other devices. The longer the cable the more this can be an issue, if you don't use XLR cables.
  2. A XLR cable can transport 48 V phantom power that some microphones need. Of course your mixer must be able to supply this phantom power, too, if you want to use these microphones.
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3  
Just to add - microphones that use phantom power are already less susceptible to noise, as the output level from the mic is higher with respect to the noise floor. So both these advantages increase the difference between the noise level and the signal level, improving quality. – Rory Alsop Feb 5 '13 at 10:11
    
It is becoming increasingly common to see balanced audio over TRS 1/4" connectors. – ObscureRobot Feb 5 '13 at 17:14
    
... but at the same time you see a lot of stage snakes going XLR-only for both sends and returns. In the rare cases where you need TRS and only have XLR, the adapter's less than $5. – KeithS Feb 12 '13 at 22:07

Fred42Vid's answer is good (though the 1/4" jack is probably a balanced TRS). I wanted to add something, though; on a mixer, when you have both a TRS and an XLR, they sometimes have subtly different signal paths. Specifically, the microphone input is often run through a second op-amp to boost its signal by about 20dBu before the main gain stage (controllable with the gain knob). This is because XLR typically carries relatively weak "mic-level" signals, while TS/TRS typically carries higher-strength "line-level" signal.

Now, this line between "mic-level" and "line-level" is very blurry, and you may find yourself boosting a weak TRS input with the gain knob, while at the same time padding or turning down a hot condenser mic. I'm just saying that very often, mixer XLR inputs get their own preamp designed specifically to boost microphone signal to working line levels, while a TRS is assumed to already be at that level.

Apart from that, the main advantage to XLR over TRS, all other things being equal, is phantom power; it is typically sent from pins 2 and 3 of the XLR input, and not from the TRS (the design of a 1/4" plug generally makes sending power along it risky; there's no positive latching mechanism, and contacts for various elements of the connector can contact other portions of the plug causing shorts and other damage). Both of these jacks are used for balanced, low-impedance connections; you don't usually plug an unbalanced, high-impedance 1/4" TS plug into a mixer (though some mixers, especially for home studios, can even deal with that).

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I'm a novice in all of this, but here are a few things that I've learned.
Condenser microphones need phantom power at (typically) 48V, Dynamic microphones do not use it. If you will be using condenser mics, ensure that your amp / preamp will provide this. A 1/4" TRS (tip ring sleeve) cable is very similar to an XLR cable in performance/function. The difference, however may be with your amp/preamp unit. I say "may", because each amp/preamp unit is different in this respect. Microphones are "low energy" devices, and therefore the signal needs to be boosted more than, say a musical instrument. For this reason your amp may provide more gain for the xlr circuit than for the TRS cable - even if they are on the same jack. For example, my Peavey Escort 3000 (a public address system) has combination XLR/TRS jacks for each of 6 channels, but the XLR and TRS are wired differently. When I use TRS cables, the microphones are very quiet, but when I use XLR cables, they are much louder - on the same channel/same volume setting. The XLR circuit power boost is "after the microphone"- it does not provide power to the microphone, it is not to be confused with the phantom power. Hope this information helps others.

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I am not an expert but my Acoustic Electric guitar has both outputs and the quality we get out of the XLR is incredible compared to the 1/4 in. But let's face it, that probably has less to do with the cable and more to do with the hardware inside of the guitar and the fact that I do not have to put a direct box between me and the soundboard. I realize that you are asking about cables for a mic, I would suggest the XLR as that is likely the connection you have on the mic and would not require any type of conversion. The short is that there is no perfect answer you need to try them both and see what sounds best as the ear test is the only way you can really know what works best with the hardware you have.

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