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Can I hook up my stereo/boom-box's line-out (headphone) to my Mac's line-in (or microphone input)? What will be the side-effects, if any?

I want to record old cassette tapes as MP3/WAV/whatever on my Mac.

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3 Answers 3

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Can I hook up my stereo/boom-box's line-out (headphone) to my Mac's line-in (or microphone input)?

Update:

tl;dr: You can connect a "line-out" to a "line-in" and all will be well.

As slhck commented below, current MacBooks have a "line-in" socket that is for "a line-level microphone" which isn't your normal mic-in socket found on typical Windows/Linux PC hardware. A line-level input should be less vulnerable than a mic-level input (though it isn't designed for a headphone output expecting a 32-ohm impedance.) Designers of modern Macs and PCs probably make provision for end-users plugging inappropriate outputs into sensitive inputs

Normally, each of the following audio interfaces are different and (at least for quality reasons) should not be mixed up

  • line-in and line-out
  • headphone out
  • microphone in

Each interface is electrically different.

Line-in is explicitly designed to be connected to line-out (on a different device usually) and vice versa. These are high-impedance, low-current signal interfaces.

Microphone-in is designed for connecting microphones, these produce much weaker signals than line-out and normally need pre-amplification before being fed to a line-in interface.

Headphone outputs are designed for relatively low-impedance devices that use a much higher signal level. It would normally be a bad idea to connect a headphone-output to a microphone-input, at best you should expect clipping and distortion.

I think some computers have connectors whose electronics can be switched in software to provide appropriate impedance etc for two different signal levels.


Update:

Stricly speaking, you should use impedance matching and attenuation in between headphone-out and microphone input. This can be done with attenuating leads, DI boxes etc

For example, the description of this product says

  • Outputs Mic Level
  • Speaker Level Input

Or this one

  • Adjustable speaker simulation
  • Balanced mic level output
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So will it be OK to put a cable between the headphone jack on a cassette player and the mic or line-in (don't know which) on my MacBook Pro? More to the point, I don't mind experimenting as long as I know I can't blow anything up. :) –  zpletan Nov 2 '11 at 19:39
1  
Again, you can't blow anything up. The Mac has a line in, the player has a line out. Just connect the two. @zpl –  slhck Nov 3 '11 at 9:02
    
@slhck, I don't doubt you. I just wanted to verify this, as RedGrittyBrick seems to indicate that caveats may apply. –  zpletan Nov 3 '11 at 15:55
    
@zpletan Sure! Luckily, Macs have been designed in a very simplified fashion: There's no mic input, and no dedicated line output. You can't even change your line-in from line to mic level. Just to reassure you: Blowing up is definitely not possible. –  slhck Nov 3 '11 at 15:57
    
@zpletan: I was hesitant to provide a definite answer because if I say (as I believe) it is highly unlikely that connecting headphone-out to microphone-in would cause permanent damage, I would hate for you to blame me when your MacBook catches fire and explodes. Anyway, connecting headphone-out to microphone-in is a very poor choice for audio-fidelity. –  RedGrittyBrick Nov 3 '11 at 16:06

Yes, you can do it but it won't be as clean as taking your tapes to a professional and having them digitized.

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Sure, just do it. You said you're on a Mac, which means that there's no separate input for microphone and line signals.

Just plug it in, using a stereo jack cable …

enter image description here

… and select the appropriate input source under System Preferences » Sound » Input. You should level the input volume so that there is no clipping (i.e. the bars shouldn't be full all the time).

enter image description here

And now you need a program to record. I suggest Audacity, which is free, open source, and comes for all operating systems.

enter image description here

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1) Will there be any negative side effects? 2) Is it possible to harm the sound card in the process, and if so, how can I guard against this? –  zpletan Nov 2 '11 at 16:58
    
There won't be any side effects whatsoever. You can't harm the sound card in any way (e.g. by giving it "too much input"). You'll just have to play with output loudness and input sensitivity settings so that your sound level is high enough. –  slhck Nov 2 '11 at 16:59

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