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First I want to say that I am totally sorry for my incompetence, but I have tried googling this and nothing came up.

So, I got my hands on an acoustic guitar and it has an output on the bottom of the body. The cable has an 1/4" audio jack and I bought an adapter to make it fit in my macbook. My question is, in order to record sound from the guitar, do I need any other devices like an amplifier or anything?

In GarageBand preferences it says 0 MIDI devices found and I can't choose anything else besides my built-in mic and also I can't hear any sound from the built-in speakers when the guitar is plugged in.

That sums it up, thanks!

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This really belongs on the Audio-Video Production site. You may find this useful: How to hook up guitar to Mac Pro? –  neilfein Nov 7 '11 at 15:09

3 Answers 3

up vote 3 down vote accepted

First, you need to understand the difference between MIDI, digital audio and an analogue electrical signal.

MIDI is a sequence of instructions like "start playing middle C at volume 200", "stop playing middle C", "shift the pitch +3" and so on. MIDI is generated by things like keyboards and sequencers, and understood by things like synthesisers and drum machines; what GarageBand calls "software instruments". It's probably not relevant to your guitar.

An analogue electrical signal is what comes out of a microphone, an electric guitar, or the transducer in your electro-acoustic guitar. It's simply a continuously varying voltage, going up and down in the same way as the sound waves that you eventually want to hear.

A digital audio signal is the computer's representation of the analogue signal - the analogue signal "sampled" into a sequence of numbers.

What you are asking, is how to convert the analogue signal from your guitar into the digital audio signal your computer needs.

Note that what you have is an electro-acoustic guitar. If it was just an acoustic guitar, it would not have any kind of socket.

First, make sure the transducer in your guitar works. A transducer is a lot like a microphone or pickup, except that it detects vibrations in the surface it is attached to, instead of having its own diaphragm or detecting vibrations in metal strings. Borrow an amplifier, plug your guitar into it, and verify that sound plays from the amp. Like microphones and pickups, some transducers are "active" and need a battery. Others are "passive" and don't need a battery. If there is no obvious battery compartment, it's likely yours is passive.

Next, you need a suitable socket in your computer. There are a few options here:

  • If your computer has a microphone socket, you can use that. It may not be ideal, but it will work
  • If your computer has a line-in socket, you can use that. However, the signal from a transducer/microphone/pickup is too quiet for a line-in. You need to first amplify the signal to line level. There are several options for this. Anything that can drive headphones is good enough -- a pocket practice amp, a multi-fx pedal etc.
  • If your computer has no built in audio input, you can add one. You can fit internal sound cards to desktop systems, or you can get USB sound interfaces. The Griffin iMic is a compact and affordable USB option. You can pay more for fancier interfaces with more inputs, professional connections (such as balanced microphone sockets), better sound quality etc.

Before trying to use these inputs in a program such as GarageBand, check that they work in the OS's control panel. This varies depending on your OS, but in both Mac and Windows, there are sound control panels where you can select an input, and watch a signal bar respond to the sound you make.

Once you know it is working, and you know the name the OS is using for the input your guitar using, telling your music application to use it should be straightforward.

Hint: in GarageBand, choose either "electric guitar" or "real instrument". Even though your instrument is electro-acoustic, follow the GarageBand help pages for an electric guitar.

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Thanks a lot, I think I understand it now. I will try tonight to plug the guitar in the line-in of my desktop PC and see if it works or not. If it doesn't work, you say that I should try to amplify the signal? I have a headset with something like a box which has line-out and mic (or line-in) ports. Can I use that to amplify the guitar? –  Nikolay Dyankov Nov 4 '11 at 11:39
Your "something like a box" sounds like it should work, although I can't promise great quality. –  slim Nov 4 '11 at 11:45
Haha, thanks ;) –  Nikolay Dyankov Nov 4 '11 at 11:55

Acoustic guitars aren't generally MIDI devices, but your computer should recognize that something is connected to the microphone jack. Mic jacks are amplified so you wouldn't want to amplify the guitar before connecting it to the mic jack. Laptops don't normally have Line In ports, but they are unamplified.

You'll need to have a battery in your guitar, usually there's a slot in the top of the body with a button and LED you can use to test if it's got enough charge. Once that's working you should also ensure that the cable is working and that you properly convert from stereo to mono or vice versa if need be. I would suspect both ports (guitar + computer) are mono so in that case you would ensure you're using mono cables and that the size converter is also mono to mono. However it appears that (some) Macbooks have combined ports, so in that case it's probably stereo. Perhaps that post can help you figure it out.

Then ensure OSX is detecting the microphone. I don't use a Mac so unfortunately I can't help with that, but there should be Sound Properties or something similar in the OS settings where you can view input levels and so on.

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Well, my guitar has two control sliders on the top - one for volume and one for passive tone control, but there isn't a slot for a battery, LED light or a button. As far as the cable, it's brand new, so I assume that It's working, as well as the adapter. But in the store they asked me if I wanted a stereo adapter or mono, and since it's going to go in a computer, I said stereo. –  Nikolay Dyankov Nov 3 '11 at 20:53
@NikolayDyankov Hmm, maybe the battery's inside? My acoustic's a little strange so I'm not sure where else to look. –  Matthew Read Nov 3 '11 at 21:52
Don't make me unscrew the bolts, please :) –  Nikolay Dyankov Nov 3 '11 at 22:11
@Nikolay Make and model of your guitar? Maybe we can help you find it =) –  jadarnel27 Nov 3 '11 at 22:47
It's a HOHNER HC06E. Btw, just found out that I don't have line-in port for my macbook, haha. But same problem on my PC, so the question still goes :) –  Nikolay Dyankov Nov 4 '11 at 7:05

Nikolay - you need an MAudio guitar connector for your macbook. It has USB to your computer, and guitar 1/4" plug in, which you need to connect an acoustic guitar pre-amp to, and either a mic or a pickup on your guitar.

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