Hardware Reference
In-Depth Information
Toreducefilesize,mostmanufacturersofaudioadaptersuseanalgorithmcalled
Adaptive
Differential Pulse Code Modulation (ADPCM) compression
(it's also called IMA-
ADPCM), which was developed by the Interactive Multimedia Association (IMA).
ADPCM reduces file size by more than 4:1. IMA-ADPCM compresses 16-bit linear
samples down to 4 bits per sample. However, a simple fact of audio technology is that
whenyouusesuchcompression,youlosesoundquality.Unfortunately,nostandardexists
for the use of ADPCM. For example, although both Apple and Microsoft support IMA-
ADPCM compression, they implement it in different ways. Apple's standard AIFF and
Microsoft's standard WAV file formats are incompatible with each other unless you use a
media player that can play both.
When you install an audio adapter, several codecs (programs that perform
co
mpression
and
dec
ompression)areinstalled.Typically,someformofADPCMisinstalledalongwith
many others. To see which codecs are installed on your system, open Windows Media
Player(version11orlater),selectOrganize,ShowClassicMenusorShowMenuBar,and
click Help, About Windows Media Player. Then click the Technical Support Information
link.Inthebrowserwindowthatopens,scrolldowntoseetheinstalledaudiocodecs.
Fig-
ure 13.4
shows a typical list of audio (and video) codecs from a system running Windows
7.
Figure 13.4
Audio and Video codecs from a system running Windows 7.
