The most common connector on analog inputs is the standard 1/8-inch phone jack that
is just like those on the earphones of your portable CD or tape player. Professional or more
specialized sound cards may include left and right stereo RCA jacks, which are 1/4-inch
phone jacks like the ones used to connect earphones to your home stereo components. The
RCA jack, named for the early sound pioneering company, is the standard for professional
studio equipment.
Other important features and components found on most PC sound cards include: Analog outputs Most sound cards have two analog output jacks. One, which
is usually identified as Phones Out or Speaker Out, (or is marked with a picture
to that effect) is powered by a small amplifier on the sound card that is capable
of producing the sound for headphones or passive speakers. The other jack,
usually labeled as the Line Out jack, produces a line-level signal that can be
used as an input to a home-stereo receiver, for example. Like the analog input
jacks, 1/8-inch phone jacks are the most common, but higher-end cards use
RCA (1/4-inch) phone jacks.
Digital I/O (input/output) This type of connector on a sound card makes it
possible to accept input or send output directly to a digital device, such as a
MiniDisc or digital audio tape (DAT), without ever converting the data from
digital to analog. This eliminates the need for the data to pass through either
a DAC or an ADC, which always has the potential to degrade or distort the
sound signal. It won’t mean much to anyone except a sound engineer, but
the most common digital interfaces used on sound cards are S/P-DIF (Sony/
Philips Digital Interface) and AES/EBU (Audio Engineering Society/European
Broadcasting Union).
Game/MIDI port This connector is commonly used for game controllers such
as joysticks or game pads. However, with a special type of cable, this port can
be connected to any external MIDI (Musical Instrument Digital Interface) device
to send and receive MIDI data. More on MIDI later.
Digital Signal Processor (DSP) Once found only on expensive high-end
sound cards, the DSP chip serves only one purpose: to relieve the PC’s CPU
of the burden for processing audio data. As DSP chips become less expensive
and are included in more and more devices, they are now finding their way
onto less expensive sound cards. DSP chips are the fastest growing segment
of the semiconductor industry as more demand is being generated for sound
reproduction in smaller and smaller devices. Among the tasks performed by
the DSP chip on a sound card are resampling (changing the bit depth and sample
rate of audio data) and adding digital effects such as reverb and echo to an audio
piece. Sampling and resampling are discussed later in the chapter.
Synthesizer Unlike digital data that is sent through the DAC to be converted
to sound, MIDI signals tell the sound card which sounds to make, at what
frequency, and for how long. In order to play back MIDI sounds, the sound(^542) PC Hardware: A Beginner’s Guide