Is a buffer the same thing as a DI?

[Halion]

I keep reading about buffers, and I'm not quite sure what they do. Is it the same thing as a DI box?

[Marek]

Heh, I guess that (among other things) a DI-Box normally has a balanced output (3-pin output: Hot, Cold, Ground for better noise rejection) and Ground lift option, can be passive (transformer) and active (JFET, OPAMP, BJT...) while under buffer we understand an electronic device used for impedance matching (wow, what a deffinition :-) ).

Please correct me if I'm wrong.

Greetings,
Marek

[Halion]

Ok, I got that far too, but isn't that exactly what a DI box also does? I know DI boxes almost always also have things like balanced outputs, groundlift switch and perhaps an attenuation switch or two, but those are not really the main functions of a DI, as far as I know.

[Mike Burgundy]

A DI could be seen as a buffer, yes.
A buffer as such is usually understood as a 1:1 amplifier used for impedance matching, and preventing whatever's behind the buffer from influencing whatever is before it (think signal splitter: two or three inputs might load an output, while a buffer will prevent this). It's an electronic building brick, as such.
A DI is a physical box, either active (employing buffers for line isolation, some electronics to produce the inverted signal, and a line driver amplifier for each signal capable of driving significant loads) or passive (transformer), used to plug a non-balanced instrument into a balanced input, using long, long lines if possible.
A buffer prevents bits of your circuit from influencing each other. A DI prevents radiowaves, EM radiation and signal degradation in long cables to influence your signal.

[Halion]

Ok, thanks for the answers :-)

Next question: If I plug my guitar directly into my soundcard (recording quality soundcard in my computer, don't worry about the AD conversion), without a buffer or DI, just a good, but ofcourse unbalanced cable (short), will that still give me impendance mismatch problems? If I build a buffer in a (stomp)box, and use between my guitar and soundcard, would that fix any impendance problems? In that case, it would work the same as a DI box would in my situation (home studio, no need for long cables, groundlift, attenuation or anything)?

[Mike Burgundy]

you could do that, yes.
A simple opamp buffer with high input impedance (the computers input Z is just waaay too low) will do. TL 072 or 071 (which are a dual and single opamp respectively, otherwise more or less identical - the 072 is easier to handle) will do nicely.
Also consider, unless you have ampfarm or something like that,building a speakersim. You can run that directly into your soundcard. Plain guitar sounds not too nice.
a search will yield lots of possibilities.

[Halion]

I know all about what I can do with the signal once it's in the computer, don't worry about the speaker simulator

[ragtime8922]

Well what about signal level? I thought a DI could bring a guitar level up to line level.  BTW, what is the level for each?

Basically, what needs to be done to plug in to a PA with your guitar?