Today, time-compression technology has
evolved from analog format to one of a digital
nature. More importantly, the technology is
real-time: audio content can be manipulated by a
learner while the audio is playing. This makes the
technology much easier to use since the learners
do not have to re-record the content at a faster
or slower rate. The key digital technology that
supports the increased or decreased playback
of audio content involves time-compression
algorithms. These sophisticated algorithms
fall into two broad categories: linear and nonlinear.
Linear time-compression applies a
consistent manipulative to the entire audio
content, irrespective of the information in the
audio recording. Short and fixed-length speech
segments (called audio gaps) are discarded, and
the retained segments are then abutted after
cross-correlation (averaging the edges of audio
frames before abutting) to diminish the effects of
abrupt audible noises (He & Gupta, 2001). The
result reduces the remaining audio segments by
equal proportions.
Non-linear time