Sorry for the stupid question, but I'm basically wondering what a 4 track recorder is? Is it basically a recording device that allows you to filter different instruments onto the same track (e.g. bass, guitar, vocals, electric drums)? I'm looking to record some rough demos so we can listen back to them and was wondering what the best option would be to do this....

A 4 track recorder is a device that allows you to record up to 4 tracks, that's it. So you could have say 2 guitar tracks, 1 vocal track and one bass track.
4 track is kind of obsolete but you could probably find one at Goodwill or something.

This is how I'd do it on the cheap presuming you have a computer:

-USB interface (I like the Presonus USB for <$100 used)
-Microphone (SM 57, $50 used)
-Software (download a free trial of Sonar/Reaper/etc)

With this kind of setup and a little skill with the software you can track fairly easily.
If you get sick of being on a computer at the end of a day then maybe you might like a good 8 track, Zoom ones are pretty slick e.g. http://www.guitarguitar.co.uk/recording-studio/detail.asp?stock=11082311063488&gclid=CP6StMnjkrsCFfHKtAoddGEA8g
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Go to the Recordings forum and read the Interfaces sticky. There's an article in that thread about multitrackers, which started out as cassette based 4 tracks and have now evolved into fully functional DAWs.
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I've still got my old 4 track cassette. One of the original Tascam Porta Studios with the fully featured mixer. I still use the mixer at times. It's actually pretty good. Never use the tape of course.
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My GNX4 multifx has an 8 track recorder built in. Evey now and then MF blows out the small digital Tascam multitrack recorders pretty cheap.
I have an old Fostex 4 track from the early 1990's. It is not what I would call very good by todays standards, but in high school I thought it was the best thing ever. Very hard to get the levels right, everything was done by headphones no visual cues like modern recorders have when you need to punch in.
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If you just want a simple rough sketch recorder you could just use your phone. Most have a recorder, no app needed.
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I have a Boss BR8 8-track unit that I rarely use anymore, but it's good for adding quick tracks that sound pretty good, and no computer startup, plugins to not work, drivers to update, etc. Quick, simple, easy and zero latency.

I also use a computer setup when I want that, and have Cubase, Ableton, Reaper and Audacity, depend on what and how I want to record or edit.

I have a Zoom surround sound recorded that pretty sweet. I use it for acoustic jams to place in the middle of everyone. Channel separation is awesome. Also great for sound effects and nature sounds, the surround sound really immersing the listener.

Mostly for ideas, I use an MP3 recorder app on my phone. I have a SoundCloud account and app. I can record a decent-sounding idea, upload it quick to SoundCloud and send that link to my band or whoever I'm working with very quickly and easily.
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