Hardware Reference
In-Depth Information
If you have only a single speaker/line out connector, you must carefully adjust your mixer
volume control and the volume control on your amplified speakers to find the best quality
sound. Don't use powered speakers with an already-amplified sound if you can avoid it.
Microphone in or mono in connector (pink) —The mono in connector is used to connect a
microphone for recording your voice or other sounds to disk. This microphone jack records in
mono—not in stereo—and is therefore not suitable for high-quality music recordings. To record
in stereo, use the line in jack. Many audio adapter cards use Automatic Gain Control (AGC) to
improve recordings. This feature adjusts the recording levels on the fly. A 600ohm—
10,000ohm dynamic or condenser microphone works best with this jack. Some inexpensive
audio adapters use the line in connector instead of a separate microphone jack. Some sound
cards use a multipurpose jack in place of a dedicated microphone jack.
Although it was once necessary to connect analog or digital audio cables between an optical drive
and a sound card to play audio CDs, current sound hardware and versions of Windows Media Player
and other media player programs support digital playback.
In addition to these connectors for analog audio I/O, many systems also have provision for digital
audio output:
Coaxial PDIF (also called SPDIF or S/PDIF) —The Sony/Philips Digital Interface receives
digital audio signals directly from compatible devices without converting them to analog format
first. The SPDIF out interface might be built into the sound card using a dedicated or
multipurpose jack. Most motherboards include an SPDIF out jack on the rear port cluster,
whereas others use a plug-in header cable to provide output.
Note
SPDIF interfaces are also referred to by some vendors as “Dolby Digital” interfaces. Coax
SPDIF connectors use cables with the standard RCA jack connector but are designed to work
specifically at an impedance of 75ohms—the same as composite video cables. Therefore, you
can use RCA-jack composite video cables with your SPDIF connectors. Although audio cables
are also equipped with RCA jacks, their impedance is different, making them a less desirable
choice.
Optical SPDIF out —This supports home theater and digital speaker systems with optical
inputs. Typical location: rear of card or external device. Motherboard-based audio solutions
may include optical SPDIF out on the port cluster (as in Figure 13.2 ) or on a header cable that
uses an expansion slot. Cards made for audio recording may also include an optical or coax
SPDIF in connection.
High Definition Multimedia Interface (HDMI) —This interface carries both high definition
video and uncompressed or compressed multichannel audio (up to 7.1). For more information,
see Chapter 12 .
Audio Signal Processing Methods
PC audio hardware processing is performed in one of three ways:
• Host-based; the CPU, under control of an audio codec and driver software, performs all audio
 
 
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