(^548) PC Hardware: A Beginner’s Guide
Digital Audio Extraction
Digitalaudioextraction(DAE)isamethodofcapturingsoundsfromanaudioCDusinga
completely digital process. DAE does not require the use of a sound card, and you can
make an exact copy of an audio CD without the signal loss typical in most digital to ana-
log conversions. DAE is a feature supported by many new CD-R drives that write to CDs.
In addition to a CD-R drive, special software is also required, which is usually bundled
with CD writing software. DAE output is typically stored in the form of a WAV file.Playback
Your Windows system is likely configured to play back certain sounds for system events
like error messages, running an application, minimizing a window, or indicating that
new mail has arrived. These sounds can be configured using the Sounds icon in the Win-
dows 98 Control Panel or the Sounds and Multimedia icon in the Windows Me/2000
Control Panel. These sounds are the most basic form of playback on your PC.
Other playback events involve more active participation from the user. A Web site or a
multimedia title such as an encyclopedia may include icons that the user clicks to hear an au-
dio file describe a topic. The audio capture software used to record sounds, such as the Win-
dows Sound Recorder, typically includes a set of tools for playing back a variety of sound
files. The Windows Media Player (see Figure 21-4), which is the companion software to the
WindowsSoundRecorder,willplaybackvirtuallyanysoundfilethatcanbestoredonaPC.
Windows includes a basic mixer, called the Windows Play Control (see Figure 21-5).
This software tool can be used to adjust the volume level of various sound events. Some
games, for instance, will send different audio events to separate channels on the sound
card: speech and digital audio to the Wave channel, CD music to the CD Audio channel,
and synthesizer output to the MIDI channel. The relative volume of these different sound
sources can be balanced using the Windows mixer, which can be accessed via the yellow
speaker icon in the taskbar notification tray. Many sound cards are bundled with a pro-
prietary and usually enhanced mixer application that duplicates and often improves on
the functions of the Windows mixer.Sound File Formats
A wide variety of sound (audio) file formats is used on PC systems. The type of file used
depends on the hardware and software used to record and play back the sound. Here are
a few of the terms and concepts you’ll need before you tackle the various file formats for
sound and video data: Frequency As illustrated in Figure 21-6, the frequency of a sound wave indicates
the tone or note of the sound wave. When the frequency is slow, the sound wave
peaks are far apart and the tone is low. A high frequency indicates the sound
wave peaks are closer together and the tone is high.