Made with multi-tracks recorders. Easy to use, but it's slowly disappearing now because of the digital recording. I won't speak more about it.
By far a lot cheaper than any other type of recording.You'll only need a computer with the right recording and mixing software.. and a bit of talent.
You can do it with a keyboard synthetizer linked with your computer by a USB port for example. It's accessibility is pretty good and it really don't use much of hard disk space.
Consist of recording by yourself ambiance sounds or instruments with a mike and a minidisc.
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