The PC 98 audio basic requirements are designed to identify the baseline operating system and hardware audio support available for existing and emerging multimedia applications. They are also designed to ensure that a minimum audio capability exists across a majority of platforms.
The advanced recommendations describe additional software and hardware features beyond the minimum requirements. These recommendations support vertical applications and provide scalability above the baseline audio capabilities by offering higher compatibility, performance, concurrency, or quality.
WDM and PC Audio. One key to the successful advancement of audio in the PC is WDM Audio class support. The architecture performs all audio processing in kernel mode, which significantly improves latency. WDM provides a method for non-Microsoft code to run in kernel mode, facilitating the development of host algorithms from multiple vendors.
WDM also provides a more complete architecture than previous generations. Code common to all audio hardware on a given bus is now part of the operating system, making for faster development with more consistent results. WDM promises to streamline development through the integration of the Windows and Windows NT driver models. Now, the same driver will work under both operating systems.
Advanced Features Enabled by PCI. Once an audio device moves beyond the basic playback and recording functions of low bandwidth material, a more advanced bus interface is required. Simple audio sample transport over the ISA bus can consume a significant portion of system bandwidth. Features that require more than two streams of audio will overload the ISA bus. Because features such as 3-D positioning use as many as eight streams of audio, a shift to PCI is necessary.
PCI audio accelerators offer another powerful feature because of the high bus bandwidth available. In the digital-ready architecture, PCI devices can perform audio processing and output either to a built-in codec or back into memory for delivery to an external digital audio device. In the external case, the host can perform final mixing and sample rate conversion (SRC) if necessary, and then can send the audio to an external USB or IEEE 1394 device.
In addition, the PCI architecture with a separate audio codec targets high-quality audio, that is, with a dynamic range of greater than 85 dB.
External Digital Audio. USB and IEEE 1394 provide excellent mechanisms for delivering digital audio to external peripherals for high-quality conversion (greater than 85 dB dynamic range) to and from analog. In the near term, the popularity of USB makes it a natural choice. In the long term, the consumer-electronics industry envisions IEEE 1394 transporting audio and video among many devices in a simple, high-performance manner.