Open an audio editing program. Mac OS X Snow Leopard (10.6) comes standard with GarageBand, which allows many editing options. But you can also use Apple’s more advanced Logic Express or Logic Pro software, or any free, Mac-supported program, such as Audacity.
Drag your MP3 file directly onto the software’s main project window. If using a multi-tracking program such as GarageBand or Logic, drag the file onto any blank “track,” or recording layer, which looks like a long horizontal bar. In the left column of your screen, you will see the track names, such as “Track 1” and “Track 2.”
Adjust the volume of your MP3 file by moving the Master Volume fader up or down. Most programs include the Master Volume fader at the top or bottom of the screen. Increase the volume if your MP3 file is too soft or decrease it if your MP3 file is too loud.
Open the EQ options. Each track (or overall project, if your software does not support multi-tracking) contains an equalizer, or “EQ.” Sometimes this appears in the left column, but sometimes it appears elsewhere. In GarageBand, for instance, you must click the “Track Info” button on the left side of the screen and then select “Details.” Check the “Equalizer” button and then click the “Edit” button to the right. In Logic, you must open your “Mixer” window by clicking “Window” on the menu bar and selecting “Mixer.” Then double-click “Channel EQ” at the top of the mixer, corresponding to the track where your recording appears.
Adjust the EQ. To give your recording more bass, raise the amount of low frequency presence (bass) using the graph or slider on your screen (depending on your software of choice). To make your mix sound brighter, lower the amount of bass or raise the amount of treble (high frequency). Adjust each frequency until you're satisfied with the sound.
Remix your MP3 file. To create new layers of your own music, you must use a multi-tracking program like Logic or GarageBand. Click a blank track, directly beneath the track where your MP3 appears, and press the “Record” button, usually appearing at the top or bottom of your screen and indicated by a small red circle. Record your new instrumentation or vocals as the MP3 plays in real time. Connect instruments and microphones directly to your computer for the best audio quality. To apply effects to an MP3 file, use the effects settings provided by your software. Double-click the track name in the left column to see a list of your effects options. In GarageBand, these appear in the right-hand column of the screen. In Logic, they appear beneath the “Inserts” column on the “Mixer” window. In Audacity, they appear under the “Effect” menu on the menu bar.
Save your revised MP3. Look for an “Export” or “Save as MP3” option, usually appearing on the menu bar. In GarageBand, “Share” on the menu bar and select “Save Song to iTunes.” In Logic, click “File” on the menu bar and then select “Bounce” (“bouncing” refers to exporting your project). In Audacity, click “File” on the menu bar and select “Export as MP3.”