Apple Final Cut Pro 5 - Manual (Page 839)

52 Part I Media and Project Management
The most important distinction is the difference between an audio clip’s peaks and its
average loudness:
 Peaks are short, loud bursts of sound. In spoken dialogue, letters like P, T, and K at the
beginning of words can result in peaks if the person speaking is close to the
microphone. In music, peaks occur at the very beginning of sounds from percussive
instruments such as drums.
 The average loudness of a clip generally determines its overall perceived volume, and
this is probably somewhat lower than the level of the peaks. In the sample
waveform, the level of average loudness appears as the densest, darkest part around
the middle. Average loudness, rather than the brief peaks, tends to influence your
decision about mixing a sound higher or lower.
Average Versus Peak Audio Meters
There are several kinds of audio meters, but two of the most common are average and
peak audio meters. Average meters react to sound somewhat slowly, and don’t show
very fast transient peaks in the signal. Peak meters react to sound more quickly,
displaying even the quickest spikes in the signal.
Since digital audio signals are restricted to a range of sample values, or amplitudes (for
example, from 0 to 65,535 when using 16-bit audio), it is important that your signal
never goes above the highest sample value. If your signal peaks, there are no higher
sample values to assign these peaks, so all the peaks are clipped, which means that they
are set to the same maximum sample value. A gently curving waveform becomes
flattened, causing unacceptable distortion. Because digital peaks must be avoided,
Final Cut Pro uses peak audio meters so you can always see the highest sample values
of your audio signal.