Master your MP3s with Audacity
With professional music software selling for hundreds of dollars, finding a comparable freeware program saves big bucks. Audacity is an open-source audio editor that offers impressive features at no cost. Once you've learned the basics of fading and trimming, you'll be able to master MP3 files for Web publishing, mobile phone ring tones, and podcasts.
If you haven't yet, download the suite of Windows plug-ins from the Linux Audio Developer's Simple Plugin API (LADSPA). When using plug-ins, remember to select the section of track you wish to affect before opening the tool. Also, if you're planning to make ring tones, check out the special tips at the end of this article.
Step 1: Adjust the gain
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One main goal of mastering audio tracks is the elimination of clipping, the buzzy distortion that occurs when signals grow too loud. With Audacity, you can see if your track is clipping by watching the green bars in the Meter toolbar. If they bounce into red while the track plays, you've got a problem. To nix the clipping, you'll need to keep the output level below 0 decibels (dB), which is the loudest volume you can attain without losing quality.
The most obvious fix is to reduce the track's gain, or volume. Unfortunately, Audacity doesn't reset its red clipping indicators until you stop and replay the track, so you'll need to adjust the sound by trial and error. Note that if your track exceeds 0dB in its original recording, you'll never be completely free of the distortion.
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Step 2: Compress your tracks
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Reducing the volume of an audio track will curb its clipping, but if you stop there, your might lose presence and force. Counter with compression. The Compressor tool (in the Effects menu) will automatically attenuate the track's volume, dramatically diminishing the gain after it reaches a specified level. It's not a hard cap--the volume can still surpass your dB setting--but tapering the sound produces a more natural, polished finish than abruptly cutting the track.
Like adjusting the gain, the Compressor may require several tries until you find a sweet spot. As a general guideline, slide the threshold between -10 and -16 dB. If you set it too low (e.g. -18) then you sacrifice definition. Set it too high (e.g., -8) and your sonic information will sprawl rather than coalesce.
After setting the threshold, experiment with the compression ratio to determine the factor of attenuation. The higher the compression ratio, the less your track will rise above the threshold.
Next, set the attack time. If you want the whole signal to compress immediately, select 0. Set the slider in the opposite direction, toward 1, for a softer attack that compresses the track after pausing a few moments. After each change to the compression tool, be prepared to wait about 15 seconds on a midrange PC for Audacity to apply the modifications.
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Step 3: Equalize!
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Equalizing can selectively increase or lower gain for any specific frequency, not just those that pass a given decibel threshold. By controlling and blending the frequencies between multiple tracks, you can tailor conflicting bass lines, or let a specific section of a track shine.
Select "Equalization" from the Effects menu, and you'll notice a horizontal line that keeps a steady 0 dB across all frequencies. Using the mouse, you'll be able to click a series of points along the scale to create a curve that associates volume--measured in decibels--with high, mid, and bass frequencies, measured in hertz (Hz). On the equalizer, low volume falls below the 0 line, and high volume rises above it. Low frequency lies from 30 to 100Hz, while high frequency ranges from 1,000 to 10,000Hz.
Clicking and dragging to curve the decibels below 0 dB on the vertical Y-axis and between 30-100 Hz on the horizontal X-axis will silence the bass line of that track, and allow the bass of another track to dominate.
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