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Sound Card Standards

As well as producing sound, sound cards double-up as CD-ROM interfaces, supporting the three proprietary interfaces for Sony, Mitsumi and Panasonic drives in addition to the increasingly popular SCSI and IDE/EIDE standards. They also have an audio connector for CD-audio output. The rationale for providing CD-support on sound cards is that it allows a PC to be upgraded to multimedia capability by the addition of a single expansion card.

The hardware configuration of the AdLib soundcard was the first standard of importance, but it has been Creative Labs’ SoundBlaster cards that have led the way in the establishment of a much-needed standard for digital audio on PC. Creative maintained its lead by following its 8-bit product with a 16-bit family, the user friendly AWE32 fulfilling the wish lists of several years’ worth of existing users. Selling this as an OEM kit for PC manufacturers helped bring prices down and specifications up. The AWE64, launched in late 1997 and offering 64-note polyphony from a single MIDI device, 32 controlled in hardware and 32 in software, is the current benchmark.

Most sound cards sold today should support the SoundBlaster and General MIDI standards and should be capable of recording and playing digital audio at 44.1kHz stereo. This is the resolution at which CD-Audio is recorded, which is why sound cards are often referred to as having CD-quality sound.

Surround sound for the movies is pre-recorded and delivered consistently to the ear, no matter what cinema or home it is replayed in. Just about the only thing Dolby cares about is how far away the rear speakers are from the front and from the listener. Beyond that it’s the same linear delivery, without any interaction from the listener – the same as listening to music.

This is obviously no good for games, where the sound needs to interactively change with the on-screen action in real time. What now seems like a very long time ago, Creative Labs came up with its SoundBlaster mono audio standard for DOS games on PCs. As the standard matured, realism improved with stereo capabilities (SoundBlaster Pro), and quality leapt forward with CD resolution (SoundBlaster 16). When you started your game, you’d select the audio option that matched your sound card. Microsoft, however, changed the entire multimedia standards game with its DirectX standard in Windows 95. The idea was that DirectX offered a load of commands, also known as APIs, which did things like make a sound on the left or draw a sphere in front. Games would then simply make DirectX calls and the hardware manufacturers would have to ensure their sound and graphics card drivers understood them. The audio portion of DirectX 1 and 2 was called DirectSound, and this offered basic stereo left and right panning effects. As with other DirectX components, this enabled software developers to write directly to any DirectX-compatible sound card with multiple audio streams, while utilising 3D audio effects. Each audio channel can be treated individually, supporting multiple sample rates and the ability to add software-based effects. DirectSound itself acts as a sound-mixing engine, using system RAM to hold the different audio streams in play for the few milliseconds they must wait before being mixed and sent on to the sound card. Under ideal conditions, DirectSound can mix and output the requested sounds in as little as 20 milliseconds.

DirectX 3 introduced DirectSound3D (DS3D) which offered a range of commands to place a sound anywhere in 3D space. This was known as positional audio, and required significant processing power. Sadly we had to wait for DirectX 5 before Microsoft allowed DS3D to be accelerated by third-party hardware, reducing the stress on the main system CPU. DirectX 6 saw the debut of DirectMusic, offering increased versatility in composing music for games and other applications.

DS3D positional audio is one of the features supported by the latest generation of PCI sound cards. Simply put, positional audio manipulates the characteristics of sounds to make them seem to come from a specific direction, such as from behind or from far to the left. DirectSound3D gives game developers a set of API commands they can use to position audio elements. Furthermore, as with much of DirectX, DirectSound3D is scaleable: if an application asks for positional effects and no hardware support for such effects are found, then DirectSound3D will provide the necessary software to offer the positional effect, using the CPU for processing.

DS3D may have supported positional audio, but it didn’t offer much support for adding reverb, let alone considering individual reflections, to simulate different environments. Fortunately DS3D does support extensions to the API, and this need was soon met by a couple of new sound standards which have gained widespread support from games developers: Aureal’s A3D technology and Creative Technology’s Environmental Audio Extensions (EAX).

Filed Under: Sound Cards

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