Hardware Reference
In-Depth Information
on an optional daughtercard. However, with the ascension of the PCI bus for sound cards and large
amounts of RAM in computers, most sound cards and integrated audio devices adopted a so-called
“soft wavetable” approach, loading 2MB-8MB of sampled musical instruments into the computer's
RAM.
Whereas early games supported only digitized audio samples (because most early sound cards had
poor MIDI support), late DOS games such as
DOOM
began to exploit the widespread wavetable-
based MIDI support found on most mid-1990s and more recent sound cards. With all current sound
hardware supporting wavetable MIDI and the improvements in DirectX 8.x and above for MIDI
support, MIDI sound has become far more prevalent for game soundtracks. Many websites also offer
instructions for patching existing games to allow MIDI support. Whether you play the latest games or
like music, good MIDI performance is likely to be important to you.
The most important factor for high-performance MIDI is the number of hardware voices. Even the
best sound cards normally support only 128 voices in hardware; the remainder of the voices required
by a MIDI soundtrack must come from software. If your sound card supports only 32 MIDI voices in
hardware or uses software synthesis only, consider replacing it with a newer model.
On Windows-based systems with integrated audio, Microsoft GS Wavetable SW Synth is used for
MIDI support.
Although most ISA and older PCI sound cards had provision for MIDI outputs via the game port or
dedicated MIDI ports, systems with modern integrated audio do not have MIDI ports. However, a
variety of MIDI input/output devices can be connected via USB ports, or you can choose a sound card
that incorporates MIDI ports (refer to
Figure 13.3
) or has a MIDI port daughtercard.
Tip
With Windows XP and older editions, you could select the MIDI output device you wanted to
use (such as a USB MIDI device or a third-party MIDI program) via the Control Panel's
Sounds applet. However, this option is not included in Windows Vista or later versions. If you
want to switch to a different MIDI output program or device with these versions of Windows,
download and install the MIDI Out Setter utility available from
Data Compression
All audio adapters on the market today can easily produce CD-quality audio, which is sampled at
44.1KHz. At this rate, recorded files (even of your own voice) can consume more than 10MB for
every minute of recording when stored as uncompressed WAV files.
To reduce file size, most manufacturers of audio adapters use an algorithm called
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 when you use such compression, you lose sound quality.
Unfortunately, no standard exists 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.
