Editing and Playback
A Quick Look Back:
Cart MachinesCart machines (cartridge machines), which are still used in a few facilities, incorporate a continuous loop of 1/4-inch (6.4mm) audiotape within a plastic cartridge.
Unlike an audio cassette that you have to rewind, in a cart the tape is in a continuous loop. This means that you don't have to rewind it, you simply wait until the beginning point recycles again. At that point the tape stops and is either cued up to the beginning, or to the next "cut" (segment) on the tape.
Most carts record and playback 30- and 60-second segments (primarily used for commercials and public service announcements) or about three minutes (for musical selections).
Audio carts are now well on their way to ▲Museums of Broadcasting along with other exhibits of broadcast technology used in earlier years. Today, audio is primarily recorded and played back on hard drives, CDs, and solid-state recorders.
of their superior audio quality, ease of control, and small size, CDs (compact
discs) have been the a preferred medium for prerecorded music and sound effects.
However, today, radio stations typically transfer CD selections to a computer
disk for repeated use.
As we've noted, for repeated use, CD audio tracks are commonly transferred
to computer disks where they can be better organized and quickly selected and
played with mouse clicks or a few strokes on a keyboard. A computer screen displays the titles
and artists, and the time remaining for a selection that's being
CD Defects and ProblemsIf the surface of the CD is sufficiently warped due to a manufacturing problem, or improper handling or storage, the automatic focusing device in the CD player will not be able to adjust to the variation. The result can be mistracking and loss of audio information.
Automatic Error CorrectionManufacturing problems and dust and dirt on the CD surface can cause a loss of digital data. Professional CD players attempt to compensate for the signal loss in three ways:
If the loss of data is more significant, error-correcting circuits can instantly generate or repeat data that more or less blends in with the existing audio. If this type of error concealment has to be invoked repeatedly within a short time span, you may hear a series of clicks or a ripping sound.
Finally, if things get really bad and a large block of data is missing or corrupted, the CD player will simply mute (silence) the audio until good data again appears — a solution that's clearly obvious to listeners.
In the second part of this Module we'll look at the latest audio recording and playback processes.
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