D. Rocchesso: Sound Processing
Time-Domain Graphical Editing and Processing
The most obvious application for inline sound processing is that of graphical
editing of sounds. While text data files lend themselves very conveniently to
musical data description, high-resolution graphics are fundamental to this spe-
cific field of applications where single-sample accuracy can be sacrificed to a
more intuitive sound event global view.
Most graphic sound editors allow to splice and process sound files in different
Sound Display
Time Scale
Envelope Shaping
Figure 7: A typical sound editing application
As fig. 7
shows the typical graphical editor displays one or more soundfiles
in the time-domain, allowing to modify it with a variety of tools. The important
concepts in digital audio editing can be summarised as follows:
regions - these are graphically selected portions of sound in which the
processing and/or splicing takes place;
in-core editing versus window editing - while simpler editors load the sound
in RAM memory for editing, the most professional ones offer buffered on-
disk editing to allow editing of sounds of any length: given the current
storage techniques, high-quality sound is fairly expensive in terms of stor-
age (ca. 100 kbytes per second and growing), on-disk editing is absolutely
essential to serious editing;
editing and rearranging of large soundfiles can be extremely expensive
in terms of hardware resources and hardly lend themselves to the gen-
eral editing features that are expected by any multimedia application:
multiple-level undos, quick trial-and-error, non-destructive editing, etc.:
several techniques have been developed to implement these features - the
most important one being the playlist, which allows soundfile editing and
rearranging without actually touching the soundfile itself but simply stor-
ing pointers to the beginning and end of each region. As can be easily
understood, this technique offers several advantages being extremely fast
and non-destructive;
The editor in this example is called Audacity, an Free Software audio editing
and processing application written by Dominic Mazzoni, Roger Dannenberg et al.[57]
( http://audacity.sourceforge.net ) for Unix, Windows and MacOs workstations.
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