Getting a sound signal to the home recorder takes several steps. The path that the sound takes from the instrument or microphone to the recorder is called the signal chain.
You need to be aware of the signal level at all these steps to get the best sound possible.Too much gain at one stage forces you to reduce the gain at another. Likewise, too little gain at one point may require you to overdrive (bump up the gain) during the next stage.
How you set the levels that you record to disk has a lot to do with how good (or bad) your performance sounds. The key to getting good recording levels is to get as hot (high) a signal as you can without going over the maximum that the converter or recorder can handle.
If you use analog tape, you have some leeway in how hot your signal can get, but if you record digitally, you don’t have that luxury. Anything over the baseline of 0dB is going to clip — a nice recording term that means distort. 0dB, by the way, doesn’t mean “no sound.” Instead, it refers to the highest level that a digital system can handle without clipping the signal.
How hot is hot enough, you ask? Well, it depends on who you talk to and at what bit depth you record:
*16-bit systems: 16-bit recording has serious limitations. This is because to record with enough headroom, you need to turn the incoming level down so much that you start to lose sound quality; that is, you’re using fewer than 16 bits and lowering the resolution of your system.
In this case, set your level higher in a 16-bit system than in a 24-bit system — usually with peaks no higher than –6dB. This allows some room for transients while preserving as much resolution as possible.
*24-bit systems: Because plenty of bits are available, you have more wiggle room before you start to lose sound quality. For 24-bit systems, record with your peak level at or below –12dB. This gives you enough room for transients to sneak through without clipping your system.
When you set your recording levels (do this by playing a section of your song), keep the following points in mind:
Keep an eye on the clip light on your preamp/input. Not all inputs have a clip light, but if yours does, it’s most likely located next to the trim knob. Sending too hot a signal through your preamp/input is the first way you can create distortion.
Your clip light should illuminate only faintly once in a while, if at all. If your clip light is glowing red, your signal is way too hot and you may end up with distortion. (Check the owner’s manual for your preamp to see when the clip light is set to activate. Some clip lights are set to go off at –6dB, others illuminate at –3dB, and still others light at 0dB.)
Use the meters as a guide. Both your mixer and recorder have meters that show you the level of the signal going in. Both of these levels are important, so keep an eye on them. Make sure that the meters never go above 0dB and that they peak out at a maximum of –12dB to –6dB. Also, be aware of whether you’re monitoring pre or post levels.
Trust your ears. Even with the clip light and meters, you still need to listen carefully to the signal. Many of the level meters on digital recorders are fairly slow to respond and can often miss sudden, extreme transients. If you hear any clipping or occasional harshness in the sound, turn down the level, regardless of what your meters tell you.
When in doubt, turn down the level. If you can’t tell whether the sound is clean, don’t be afraid to turn down the level a little. Recording at –16dB instead of –12dB isn’t going to ruin your track, but a clipped note can.
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Source:http://www.dummies.com/how-to/content/setting-optimal-sound-signal-levels.html
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