The Normalization of Your Audio File

This should be the last step in editing your audio files before converting them to MP3 or burning them to disc. Normalization ensures that a track's volume level is as high as it can be without going over 0 dB, causing unpleasant sounding digital errors known as "clipping".

Most audio editing software will allow basic normalization, which is a very simple process. The software scans the waveform for peaks, and then increases the volume of the entire file so that the highest peak does not exceed a stated limit. In Adobe Audition, simply choose Effects > Amplitude > Normalize [process]. If the track was not already selected, it will select the entire track by default, and you will be presented with a very simple dialog box. Digital audio professionals will usually advise that you do not select 100 percent on a 16-bit track using a setting of about 95 percent will prevent "stray" frequencies from going over the limit. If you opt to select the Decibels Format checkbox, you can enter the peak value in decibels, which should be set to -0.1 dB. A fraction of a decibel will not make much difference, as one decibel is a relative measure of the smallest perceptible difference in volume.

Ensure that Normalize L/R Equally is selected so that both channels are kept at the same level in relation to one another, and click OK to begin processing. If your audio file was clipping because of EQ settings or other processing, you may see the volume level go down a little.

If you are editing digital audio files that you recorded yourself, it is possible that you managed to get the levels right, but they just sound too quiet. Sometimes, merely normalizing all your tracks may not help at, all because the perceived volume is simply not high enough. While this can often be resolved in the equalization stage, it may be easier to apply "hard limiting" to the entire track in order to make it sound "louder."

Hard limiting boosts all frequencies by a set amount, but attenuates (compresses or reduces, depending on the method used by your software) frequencies that would otherwise clip. If you have ever wondered why TV commercials sound so much louder than the regular shows, it is because extreme levels of hard limiting have been used to give the ads more perceived volume and impact while still keeping them under a required decibel level. While it may sound like a good idea to use this method on all your tracks, remember that it reduces the details and the dynamics of your track, and can also increase hiss and other noise on recordings from vinyl or cassette.

To use this feature in Audition, choose Effects > Amplitude > Hard Limiting (Process). In the dialog box that appears you should set Limit Max Amplitude (volume) to the same amount you would in the normalization process, so -0.1 dB is best. The default amount for Boost Input is 6dB, this is high! Try 2dB instead.

Lookahead Time is the amount of time allowed for the processor to attenuate (reduce) the peaks, and Release Time is the amount of time allowed for the level to return to normal. These are measured in milliseconds, so the default settings of seven and 100 respectively will probably be sufficient. These rapid volume changes should be imperceptible.

Make sure Link Left and Right is checked, and click the Gather Statistics Now button. The values in Percent Clipped tell you how much of the audio would exceed 0 dB without limiting. Change the Boost Input value to 3dB and click Gather Statistics Now again-note the higher percentages. Test your track using the Preview button, and when you are satisfied, click OK.As with EQ, hard limiting is usually best kept to a minimum, as every music player has a volume control, and excessive processing usually reduces the musical detail in a track, even if it gives the amateur digital audio enthusiast a thrill to make "everything louder than everything else". Moreover, it can be jarring for random tracks on one album to burst forth with much higher volume levels than others, a phenomenon that may be indicated by the worn Mute button on your television remote control.