Apple Logic Pro 9 - Manual (Page 606)

Getting to Know the Strip Silence Window
The main parameters of the Strip Silence window are as follows:
• Threshold: Use to define the amplitude level that a passage must exceed, in order to
be defined as a region. In terms of the number and length of regions created by the
process, this is the most important parameter. As a general rule: a higher Threshold
value leads to numerous short regions. Low values create fewer large regions.
• Minimum Time to accept as Silence: Use to define the length of time that a section must
be below the Threshold value, before it is considered a gap. Very small values tend to
increase the number of regions, because even short dips in amplitude are interpreted
as silence. Higher values prevent sections of audio from being interrupted by fluctuating
amplitudes.
• Pre Attack Time: Use to add a defined amount of pre-roll to the beginning of all regions
created by the Strip Silence process. High threshold values prevent any amplitudes
with slower attack times from being chopped. This function is useful for nonpercussive
material such as vocals, wind instruments, strings, and so on. Overlaps are
permitted—the pre-delayed start point of a region can extend back to the end of the
previous region—but only if the Threshold value is not exceeded. The Pre Attack Time
doesn’t affect the anchor position, which means the absolute position of the audio
data (in the project) is retained.
• Post Release Time: Use to define an automatic release time for the end points of all
regions, avoiding abrupt cutoffs to amplitudes that fade out gradually (particularly if
you have set a high Threshold value); for example, cymbals, open hi-hats, snares with
long reverb tails, vocals, and so on. This parameter does not allow overlaps. This means
that region end points cannot extend beyond the start point of the following region.
The Post Release Time doesn’t affect the anchor position, which means the absolute
position of the audio data (in the project) is retained.
606 Chapter 19 Removing Silent Passages from Audio Regions