Hardware Reference
In-Depth Information
recently installed hardware in a category becomes the default, but you can switch back to the
original audio hardware through the Windows Control Panel Sound properties sheet.
Beyond the ability to add audio to almost any recent system, USB-based audio is particularly
appealing if your current sound card or onboard audio doesn't support 5.1 or 7.1 audio, can't
digitize sound at 24-bit/96KHz rates, or lacks digital outputs.
Before you purchase a new sound card or USB-based audio solution for a desktop computer,
you should check your system or motherboard documentation to see whether you already have
six-channel audio onboard. If your motherboard features six-channel (5.1) or better audio
output but the only ports built into the rear of the motherboard are for a normal stereo (2.0/2.1)
configuration, you need to add a header cable to the motherboard. If the motherboard did not
ship with the header cable, contact the vendor.
Volume Control
With virtually all recent sound cards, the volume is controlled through a Windows Control Panel
speaker icon that can also be found in the notification area/system tray (near the onscreen clock). If
you're switching from a bare-bones stereo sound card to a more sophisticated one featuring Dolby
Digital or analog 5.1, 6.1, or 7.1 output or input, you need to use the mixing options in the volume
control to select the proper sources and appropriate volume levels for incoming and outgoing audio
connected to the card or a breakout box. Keep in mind that if you are sending sound to an external
audio receiver, you need to adjust the volume on that device as well. Don't forget to enable digital
output via the Sound Properties playback dialog if you are using the SPDIF output jack.
If the PC speakers are amplified but you aren't hearing sound, remember to check that the power is
on, the volume control on the speakers is turned up, and the correct speakers are selected and
properly connected.
MIDI Support Features
At one time, when evaluating audio adapters, you had to decide whether to buy a monophonic or
stereophonic card. Today, all audio adapters are stereophonic and can play music using the MIDI
standard, which plays scores using either synthesized instruments or digital samples stored on the
audio adapter or in random access memory (RAM).
Stereophonic cards produce many voices concurrently and from two sources. A voice is a single
sound produced by the adapter. A string quartet uses four voices, one for each instrument. On the
other hand, a polyphonic instrument, such as a piano, requires one voice for each note of a chord.
Thus, fully reproducing the capabilities of a pianist requires 10 voices—one for each finger. The
more voices an audio adapter is capable of producing, the better the sound fidelity.
Early audio adapters used FM synthesis for MIDI support; the Yamaha OPL2 (YM3812) featured 11
voices, whereas the OPL3 (YMF262) featured 20 voices and stereophonic sound. However, virtually
all audio adapters today use recorded samples for MIDI support; audio adapters using this feature are
referred to as
wavetable adapters
.
Wavetable audio adapters use digital recordings of real instruments and sound effects instead of
imitations generated by an FM chip. When you hear a trumpet in a MIDI score played on a wavetable
sound card, you hear the sound of an actual trumpet, not a synthetic imitation of a trumpet. The first
cards featuring wavetable support stored 1MB of sound clips embedded in ROM chips on the card or
