Noise (and why you should get rid of it).

I want you to try a little experiment, start shaking your hand, and while doing so pick up a pen and write your name. If it seems a bit silly to expect your writing to be neat, or nice to read, then spare a thought for your speakers.

If you are feeding your speaker a noisy signal, your speaker has the audio equivalent of Parkinson's. You can't expect it to reproduce a sound accurately if it's shaking randomly in all directions first. How good would an orchestra sound in an earthquake?*

Noise is that hiss and hum you get when you should have silence. The problem is, it doesn't just go away when the music plays. 

There are a few likely culprits for creating noise.

One of which is your input source. That is to say the music you are listening to. To check for noise in your music, one of the best ways I have found is listening to a quiet part of the song. Usually at the beginning of a song there is a quiet part before the music starts. Can you hear a hiss? If so, the recording is probably poor! Try finding a better quality song, if you want to hear it in its full glory.

Another terrible source of noise is your amplification. What usually happens is the input volume (e.g. the volume in foobar2000, iTunes, and/or your computer) is set too low, and the volume of your amp is set too high. This will usually be obvious as you will be able to hear a hiss when the speaker is not playing anything. Usually the volume from your PC or other input source should be about 3/4 of the way up.

Another way to set your input volume is to keep your amplifier (i.e. speaker volume) at a fairly low setting. Play a track, and while you do so, keep turning up your input volume. As soon as you get distortion, or the music does not seem to be getting any louder, back off the volume a bit until it starts losing volume a very little bit or the distortion (fuzziness, harshness) disappears.

This way, regardless of how noisy your amplifier is, you will have minimized it.

The last culprit, unfortunately is the point at which you might need to spend money. If your laptop, CD player, PC, or car stereo is creating noise or distortion you may want to replace it, because there is really little that can be done to work around it!

One of the best ways to improve the sound quality of a computers output is by improving the sound card. Before you panic, this doesn't necessarily mean pulling your computer apart. I think the cheapest, and best value way of improving a sound car is just buying an external one.

An external sound card is a great idea, because it gives you the ability to have good sound quality no matter what machine you're using. If you want to change or sell your machine, you just take the card with you.

A good, cheap example of an external sound card is the Soundblaster X-fi Go! It's readily available and retails for about $35US. If you're looking for a fix for bad input, it wouldn't be a bad place to start.

Best of luck in your noise reducing quest! If you have any questions, feel free to ask.

*I'm aware that an earthquake isn't exactly random motion, but if you take into account the stumbling musicians, the wild gesticulations of the conductor, and the tuba player colliding through the percussion section, random motion, and thus noise is approximated.