Just something I've always wondered—most sound cards have both a line in and a microphone, and I've never been able to tell the difference between anything recorded with them. Lately I've seen cards without the line in, so is there actually a difference? If so, specifically what should they be used for?


6 Answers 6


Line in will usually be stereo and about 10Kohm impedance.

Mic in is mono and about 600-1Kohm impedance and expecting SIGNIFICANTLY lower levels than the line, as it has a preamp to pick up the very low levels present in a microphone.

Sometimes microphone in have XLR connector to allow Phantom Power


A microphone input is typically a very low level signal, and is mono. A line in will be expecting a much higher input level, and will usually be stereo.

The sound card should have an additional pre-amp stage for the mic to bring it up to line levels.


Line in is an audio input normally around 150mv line sensitivity and can be used for devices such as tape players,cd players,mp3 players etc.

It cannot be used as a microphone input as you would hardly hear it, a microphone input needs to see an input sensitivity of around -5 mv input,as cd players and mp3 players already have an output of around 100+mVolts the line in input is ideal and normally has flat response sound.

Other inputs such as a record player/turntable input has a tailored frequency response to suit record / vinyl only, although it's input sensitivity is similar to the microphone input of around 5mVolts, if a microphone were to be plugged into this input,it would work and you would hear it BUT the frequency(i.e. Bass,mid and treble) wouldn't be a flat response and would sound wrong.

Hope all this info helps somebody

  • Hi rob could you do an effort with the layout next time . Thanks in advance.
    – JSmith
    Jun 8, 2016 at 16:20

If you have a mic plugged in, and some other input in Line In, your computer's operating system will (or should) use the mic when you're using Skype or something. That way you don't have to do any configuration to have the mic work properly.

On good cards, the mic line will have lower impedance and should be mono. If you try to use it for something else the sound will be distorted.

  • Standard PC sound cards typically only have one input. Sounds from the mic/line/CD/etc. inputs are mixed together. The OS doesn't have anything to do with selecting which inputs are chosen. Skype or other software handles this. It isn't recording from a particular jack either... it just adjusts the mixer correctly, so that the mic isn't muted or something.
    – Brad
    Dec 26, 2010 at 19:08
  • 1
    I've never owned a sound card, onboard or otherwise, that mixed the inputs. And there's plenty of software that uses the device selected by the OS for "Recording" rather than managing things itself.
    – Matthew Read
    Dec 26, 2010 at 20:25

generally mike input is for electret mic. which has in build small circuit with mosfet it needs some power which is called biasing power the mic input is also capable to supply this biasing voltage, which is not required in line in

  • 1
    This has nothing to do with why sound cards have a mic and a line input. The difference is the signal level of the signal expected to be delivered. Phantom power is not normally provided by a mic line on a computer. Even on professional devices, it is typically an additional setting.
    – AJ Henderson
    Nov 5, 2015 at 15:20
  • interesting that this has so many downvotes. I've spent a good few hours reading around this exact subject over the past couple of days, and actually stuck a multimeter on a mic input and I'm pretty sure this answer is actually correct. I'm not saying the signal levels aren't also part of the difference, but the most common sound cards do supply bias voltage on the ring of the 3.5mm TRS connector, and the common electret PC mics won't work at all on the line input as a result. Random google hit: hobby-hour.com/electronics/computer_microphone.php
    – CupawnTae
    Apr 16, 2020 at 21:03
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    I found this answer helpful, upvoted. It answers a part of the question, contains (AFAIK) only correct information, which is not found in the other answers.
    – simon
    Aug 4, 2020 at 6:05

A side note that's probably not so important, but I think of it as Mic Input is for weak signals and Line In is for Boosted Signals like from a Guitar Amp.

(As some have already mentioned Mic into Line-In would be Quiet which can sometimes be favourable if you plan to boost the signal later - but if you put a Guitar Amp signal into your Mic it'll probably not go so well)

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