Audio Interfaces

When it comes to audio harware, the more you spend the better it will be.  In general anyways...once you get over $500 they start to be tailored for specific uses - usually for DAW's like Pro Tools or Nuendo.  I prefer Firewire but it's a bit more expensive.  I don't fully trust USB interfaces due to inherent limitations, but they might be better these days.  The general rule is Firewire is faster than USB, and Cardbus/PCMCIA is faster than firewire.  M-Audio has very good, inxpensive interfaces.  Something with a built-in MIDI port might help you if you don't have a USB MIDI interface.  You will want a built in pre-amp, and I find that a 1/4" headphone output is very useful.  All pro audio interfaces should come with their own ASIO driver.  I have heard that some are inconvenient or undependable.  I've heard especially bad things about the PreSonus Firestation and M-audio Quattro.  Harmony Central is one good place to check out user reviews.

If you are just playing around with this idea, you can get by with the built-in headphone output of a computer.  You will need to get some audio adaptors (radio shack will do) to convert your instrument cable.  The ASIO 4 All driver is an absolute necessity to do this.  The built in sound handling of Windows is very slow and you will have up to a 1 second delay from when you hit a note to when you hear it.  FYI: The "asio drivers" included with Cubase and Nuendo will not help the situation much because they don't actually interface your hardware.

ASIO Drivers and Latency

Even if you have your ASIO driver installed you may still hear a delay from when you hit a note to when it comes out of the audio interface.  This delay is called "Latency", it is measured in Milliseconds (ms), and is usually adjusted by changing a "buffer size" setting.  ASIO drivers usually need some tweaking from their default settings, and some interfaces simply can't reduce the latency low enough.  Many USB ones such as the M-box aren't good enough for me.  Before you give up on a live laptop, you should know that every digital processor or dsp pedal has latency - usually from .5-3ms.  They just don't tell you because people can't hear it.  There are some players (Thomas Diethelm) who make a big deal about how far their amplifier is from their head because of sensitivity to natural latency.  So if you can get the latency of the ASIO driver down low enough it shouldn't bother you.  Dont be a snob about not wanting to deal with latency if you didn't know it was already part of your other hardware.

So why is it such a big deal, why dont ASIO drivers just come at their fastest setting?  Because the smaller the latency, the more it uses your processor.  If your computer is thinking too hard there will be clicks, pops, or gaps in the output when it loses the pace.  For this reason it is important not to have a bunch of programs running and have as fast a computer as you can afford.  Don't freak out, slower computers can do a lot, and a high quality audio interface helps.

So you are faced with this game:  reduce the buffer size of your ASIO driver until your output clicks, then raise it back one setting.  You may need to raise it again after you start using more plugins since they are sharing the processor with the driver.  If you are playing guitar 128 samples is probably the highest you will want to go (about 6ms).  For keyboards I can deal with 256 because the sound is only going out, not coming in so the latency is cut in half. 

What is a buffer?  As the computer brings in the audio it is sliced into thousands of samples (Usually 44,100 samples per second).  It needs to get the sound back out as fast as possible so it scrapes off a tiny part at a time, processes it, and spits it out.  That tiny part is a buffer.  The smaller the buffer size, the less time that passes between the input and output.  Think about it this way:  If the computer collected one whole second worth of samples it would have wait one whole second to do it.  This process happens with ANY modern digital gear - there is usually a buffer size of 16 samples in hardware units like the Line 6 DL4 or Lexicon Jam Man.