Audacity - trying to amplify without clipping

I'm trying to make one of my songs from GarageBand louder. So I opened it with Audacity, went to Effect > Amplify, but it won't let me increase the dB level without selecting "Allow Clipping."

Isn't clipping bad? Why can I only amplify it by allowing clipping?

I wouldn't use an effect to make your sounds louder. First I would open whatever mixer GB or audacity has (not familiar with either to a great extent) and simply increase the channel level either by the input gain or fader or both if you need that much more. Be careful to not get into digital overload on the channel. Analog distortion is good. Digital distortion is bad.

You can also use compression on the track(s) and use the gain make-up to increase the level. This is what the pros do when mastering their final mixes in order to bring the signal up to spec for release. This phenomenon has led to increasingly louder releases over the last decades. If you check out recordings from the 60's to the 90's they have gotten progressively louder and more trebly (is that a word?).

Hope that helps. Like I said I am not familiar with those two programs specifically, but audio is audio, mixers are mixers, and all of these programs pretty much do the same things in the same ways.

The Hard Limiter is the crucial step that you are missing..
I used to use audacity to master my tracks when I used a PC. A few years back, they changed the way the hard limiter plug-in works and made it a little more confusing. I don't use audacity anymore, but if you see the hard limiter in the effects list this is what you do:

Set the limiter's threshold to somewhere around -6 dB. For whatever reason, most non-maximized audio tracks have the majority of the signal data peaking at around -6 dB, with occasional peaks close to, but hopefully not over 0 (which would mean that you're recording has already clipped and needs to be redone.) The -6 dB is a rule of thumb and each project will vary obviously.

Hard-limit the track to -6 dB. This is a "brick wall" compression, meaning all sound level is squished like a sponge to the -6 dB line.

NOW run the Amplifier and BOOST the track up 6 dB, or maybe 5.9 or whatever to be safe. Don't allow clipping, but if you do the math here you can see that shouldn't matter.

This will maximize the signal data of your track without digitally distorting it..

ALSO
You should be able to find a freeware limiter plug-in that can be used in GarageBand. I think it even comes with one.

Happy Mastering

I guess I had to download a LADSPA plug-in for this effect. However, I can't find it after installing to drop in the plug-ins folder. Where's the default location on my Mac?

Also, here's a weird thing: After amplifying it in Audacity, the MP3 sounds pretty good in Cog (music player). But when I play it in iTunes or on my iPod in my car, it sounds significantly quieter. Could I just be going crazy?

Anyway, here's a clip of the song in question after amplifying in Audacity: http://makeoutmusic.knoxware.org/gossipculture/mp3/reaching for territo#15DD10.mp3

It sounds OK, right? Perhaps it could sound a little more in stereo. Keep in mind I'm not trying to mix and record the greatest thing ever, just something that isn't so quiet that listeners have to adjust their volume just for me.

SCRATCH THAT LAST POST.

I downloaded Audacity 1.3 and got the Leveller effect. I set the levels as follows: Leveller at -80dB (couldn't set to -6dB like you suggested) and Amplify at 2.3dB. And wow, the combination of these two effects seem to have worked! Thank you so much.