Scalable Audio for 3-D Games

WDM audio supports the following features specifically for 3-D games under Windows 98 and Windows NT 5.0:

Software emulation of legacy hardware to support MS-DOS–based games. WDM drivers, which run in kernel mode, provide virtual Sound Blaster Pro, MPU 401, and legacy joystick interfaces.
A standard interface for the application to provide multiple streams of 3-D–positioned audio. DirectSound 3-D supports software-simulated 3-D (pan and volume) and true HRTF 3-D processing at 22.05 kHz, or hardware acceleration. The architecture supports optimal configuration based on CPU performance and installed hardware.
A wave-table General MIDI synthesizer entirely in kernel-mode software. This provides 24 voices of music synthesis with 22.05-kHz output. DirectShow, DirectMusic, MMSYS, and virtual MPU 401 can use the synthesizer functions. The architecture supports optimal configuration based on CPU performance and installed hardware.
A high-quality kernel-mode software SRC capability, which converts data streams (including composite mixes of all 11.025-kHz or 22.05-kHz sources) to the final output mix format, typically 16-bit 44.1 kHz (general SRC support includes other rates).
A kernel-mode system-wide software mixer, which supports DirectSound, DirectShow, and MMSYS clients, plus kernel-mode WDM filters, including Red Book CD-ROM and MIDI drivers. The mixer implements highly optimized, same sample rate PCM mixing at 8-bit or 16-bit 11.025, 22.05, 44.1, and 48 kHz (general mixing support includes other formats).
Flexible control of the output destination. The WDM drivers can send the master 16-bit 44.1-kHz or 48-kHz or other format output to an ISA, PCI, USB, or IEEE 1394 audio device. Additionally, support is provided for redirection of PCI-device final-mix output to USB speakers.

The minimum PC 98 audio hardware support necessary for 3-D games is built-in or external audio codec support for playback of 16-bit stereo PCM data at a 44.1-kHz sample rate. For a list of the PC 98 requirements, see the “Basic Audio Requirements” section later in this chapter.

The system designer might choose to include the following optional software or hardware in order to provide additional capabilities:

Hardware that provides legacy MS-DOS–based interfaces for compatibility with games (Sound Blaster Pro, FM synthesizer, MPU 401, game port)
Hardware for higher quality or concurrency DLS wave-table MIDI synthesis, with associated mixing and SRC support
Hardware for higher concurrency HRTF 3-D positional audio, with associated mixing and SRC support
Digital-ready, WDM-compatible MIDI and HRTF 3-D hardware acceleration

The following table presents actual measurements collected by Intel Architecture Labs (IAL) for scalable audio for 3-D games on Intel Pentium II processors with Intel MMX technology.

Performance Measurements for Scalable Audio for 3-D Games

Function	233-MHz Pentium II processor¹
Wave-table MIDI synthesis, 24 voices at 22.05 kHz	5%
Mixing with pan and volume for simulated 3-D, eight stereo streams at 22.05 kHz	3%
SRC, upsampling of the stereo composite mix of all 22.05-kHz sources to 44.1 kHz	2%
Audio effects (reverb, tone, or pseudo 3-D), stereo at 44.1 kHz	2%
Audio sample transport to PCI or USB codec	2 – 4%
Total with simulated 3-D	14 – 16%
HRTF 3-D with cross-talk cancellation for speakers, eight streams at 22.05 kHz	12%²
Total with true HRTF 3-D	23 – 25%
¹Actual performance is dependent on specific processor, chip-set, memory, and I/O subsystem implementations, as well as the software implementation (integer, floating point [FP], or MMX technology). To estimate the performance on other processor speeds with MMX technology, use a ratio based on the processor’s MHz rating. ²HRTF 3-D performance is based on the 3Q1997 release of Intel 3D Realistic Sound eXperience (RSX); performance of the 1Q1997 3D RSX is 20 percent.