Digital Sound & Music: Concepts, Applications, & Science, Chapter 1, last updated 6/25/2013
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The

" or 3.5 mm phone plug shown in Figure 1.30 is very similar to the ¼" plug, but it's
used for different signals. Since it's so small, it can be easily used in portable audio devices and
any other audio equipment that's too compact to accommodate a larger connector. It has all the
same strengths and weaknesses of the ¼" plug and is even more susceptible to damage and
accidental disconnection. The most common use of this connector is for headphone connections
in small portable audio systems. The weaknesses of this connector far outweigh the strengths.
Consequently, this connector is not widely used in professional applications but is quite common
in consumer grade equipment where reliability requirements are not as strict. Because of the
proliferation of portable audio devices, even high-quality professional headphones now come
with an

" connector and an adapter that converts the connection to

". This allows you to
connect the headphones to consumer grade and professional grade equipment.
Figure 1.30 3.5 mm or

" plug
The RCA connector type shown in Figure 1.31 is used for unbalanced signals in
consumer grade equipment. It's commonly found in consumer CD and DVD players, home
stereo receivers, televisions, and similar equipment for audio and video signals. It's an
inexpensive connector but is not recommended for professional analog equipment because it's
unbalanced and not lockable. The RCA connector can be used for digital signals with acceptable
reliability because digital signals are not susceptible to the same kind of interference problems as
analog signals. Consequently, the RCA connector is used for S/PDIF digital audio, Dolby
Digital, and other digital signals in many different kinds of equipment including professional
grade devices. When used for digital signals, the connector needs to use a 75 Ohm coaxial type
of cable.
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