DirectSound

Source: Wikipedia, the free encyclopedia.

DirectSound is a deprecated software component of the Microsoft DirectX library for the Windows operating system, superseded by XAudio2. It provides a low-latency interface to sound card drivers written for Windows 95 through Windows XP and can handle the mixing and recording of multiple audio streams. DirectSound was originally written for Microsoft by John Miles.[1]

Besides providing the essential service of passing audio data to the sound card, DirectSound provides other essential capabilities such as recording and mixing sound, adding effects to sound (e.g.,

echo, or flange), using hardware accelerated buffers (if the sound card supports hardware audio acceleration) in Windows 95 through XP, and positioning sounds in 3D space. DirectSound also provides a means to capture sounds from a microphone or other input and controlling capture effects during audio capture.[2]

After many years of development, today DirectSound is a mature API, and supplies many other useful capabilities, such as the ability to play multichannel sounds at high resolution. While DirectSound was designed to be used by games, today it is used to play audio in many audio applications. DirectShow uses DirectSound's hardware audio acceleration capabilities if the sound card's hardware audio acceleration capabilities exist and are exposed by the audio driver.[3]

Features

DirectSound is a

user mode API that provides an interface between applications and the sound card
driver, enabling applications to produce sounds and play back music.

DirectSound was considered revolutionary when it was introduced in 1995, as it featured multiple simultaneous audio streams and allowed several applications to access the sound card simultaneously. Before that, the game developers were required to implement their own audio rendering engine in software.

DirectSound provides

sample rate conversion and sound mixing (volume and pan
) for an unlimited number of audio sources; however, the practical limits are the number of hardware audio sources and the performance of software mixers.

The DirectSound architecture features a concept of the "ring buffer" which would be continuously played in a cycle. The application programmer creates the sound buffer then continuously queries its state through the "read cursor" and updates it with the "write cursor". There are two types of buffers - a "streaming" buffer, which holds continuous sounds such as background music, and a "static" buffer which holds short sounds.

On supported sound cards, DirectSound would try to use "hardware accelerated" buffers, i.e. the ones which either can be placed in local sound card memory, or can be accessed by the sound card from the system memory. If hardware acceleration is not available, DirectSound would create audio buffers in the system memory and use purely software mixing.

Some late DOS-era "

double buffering. Later cards such as Sound Blaster Live!
, Audigy and X-Fi are capable of accessing the system memory buffers directly.

DirectSound3D

DirectSound3D (DS3D) is an extension to DirectSound introduced with DirectX 3 in 1996 with the intention to standardize

API
instead of rewriting code numerous times to work for each audio card vendor.

In DirectX 5, DirectSound3D gained the support for sound cards that use third party 3D audio algorithms in order to accelerate DirectSound3D properly, through methods approved by Microsoft.

In DirectX 8, DirectSound and DirectSound3D (DS3D) were officially merged and given the name DirectX Audio, however the API is still commonly referred to as DirectSound.

EAX

Main article: Environmental Audio Extensions

EAX is an extension to DirectSound and DirectSound3D which provides sound effects processing to the hardware-accelerated buffers.

OS Support

Windows 95

In Windows 95, 98 and Me, the DirectSound mixer component and the sound card drivers were both implemented as a

blue screen
errors.

Windows 98 introduced WDM Audio and the Kernel Audio Mixer driver (

hardware mixing (also known as hardware buffering or DirectSound hardware acceleration), DirectSound buffers directly to the rendering device.[4] If DirectSound streams use hardware mixing, KMixer and its latency delay are bypassed.[5]
On Windows 98 and Windows Me, WDM audio drivers were preferred but compatibility with VxD driver model was preserved.

Although Windows Driver Model (WDM) was available starting with Windows 98, few audio card manufacturers used it. Due to internal buffering, KMixer introduced significant processing latency (30 ms on then-current systems). Windows 98 also includes a WDM streaming class driver (Stream.sys) to address these real time multimedia data stream processing requirements. When the sound card uses a custom driver for use with the system supplied port class driver PortCls.sys or implements a mini-driver for use with the streaming class driver, applications can bypass the KMixer completely and use the kernel streaming interfaces instead to reduce latency.

Windows 2000/XP

In Windows 2000, Microsoft also implemented the same WDM-based audio stack on

Acoustic Echo Cancellation
for USB microphones, noise suppression and array microphone support.

Windows Vista/Windows 7

Windows Vista features a completely re-written audio stack based on the

MME are emulated as WASAPI Session instances. DirectSound runs in emulation mode on the Microsoft software mixer. The emulator does not have hardware abstraction, so there is no hardware DirectSound acceleration, meaning hardware and software relying on DirectSound acceleration may have degraded performance. It's likely a supposed performance hit might not be noticeable, depending on the application and actual system hardware. In the case of hardware 3D audio effects played using DirectSound3D, they will not be playable; this also breaks compatibility with EAX extensions.[9]

Third-party APIs such as ASIO and OpenAL are not affected by these architectural changes in Windows Vista, as they use IOCtl to interface directly with the audio driver. A solution for applications that wish to take advantage of hardware accelerated high-quality 3D positional audio is to use OpenAL. However, this only works if the manufacturer provides an OpenAL driver for their hardware.[10]

Windows 8

WASAPI audio stack in Windows 8 introduces support for "hardware offloading" of multiple audio streams to the audio card for mixing and effect processing, in addition to the software processing introduced in Vista,[11][12] however the functionality is only exposed for Windows Runtime apps.[13] DirectSound's and DirectMusic
's hardware interfaces to sound card drivers are not implemented.

Windows CE

Although DirectSound support was available in

Windows CE versions up to 4.2, it was removed starting 5.0.[14]
Windows CE 6.0 also does not support DirectSound, instead favoring that applications be rewritten to use the Waveform Audio API.

Replacement implementations

After the removal of DirectSound in Windows Vista, a few replacement implementations have appeared.

Sound Blaster's Creative ALchemy (2007) provides hardware acceleration of DirectSound3D and Audio Effects, such as EAX.[15] Creative ALchemy intercepts calls to DirectSound3D and translates them into OpenAL calls to be processed by supported hardware such as Sound Blaster X-Fi and Sound Blaster Audigy. For software-based Creative audio solutions, ALchemy utilizes its built-in 3D audio engine without using OpenAL at all.

Realtek, a manufacturer of integrated HD audio codecs, has a product similar to ALchemy called 3D SoundBack. C-Media, a manufacturer of PC sound card chipsets, also has a solution called Xear3D EX, although it works instead by intercepting DirectSound3D calls transparently in the background without any user intervention.

IndirectSound is a freeware library that emulates DirectSound 3D using XAudio2, without using hardware acceleration.[16]

DSOAL is an open source library that emulates DirectSound 3D and EAX using OpenAL. Either a hardware-accelerated OpenAL implementation or OpenAL Soft (which provides HRTF) can be used.[17]

See also

References

  1. ^ "The Evolution of DirectX". Maximum PC. 3 (9): B8. October 1998. Retrieved July 21, 2019.
  2. ^ DirectSound Capture Effects: MSDN
  3. ^ DirectShow FAQ
  4. ^ DirectSound Driver Models
  5. ^ Overview of DirectSound Hardware Acceleration
  6. ^ CakeWalk - Windows Pro Audio Roundtable
  7. ^ Exposing Hardware-Accelerated Capture Effects
  8. ^ "Techreport article on Vista-ready soundcards". 15 January 2008. Retrieved 2008-12-23.
  9. ^ Creative Technology - Support - Audio in Windows Vista
  10. ^ "OpenAL and Windows Vista". Archived from the original on 2008-01-02. Retrieved 2008-01-10.
  11. ^ Audio Offloading: Exposing Hardware-Offloaded Audio Processing in Windows
  12. ^ Windows Driver Kit - Windows Developer Preview - New for Audio Drivers
  13. ^ "Implementation Overview - Windows drivers | Microsoft Docs".
  14. ^ Windows CE 5.0 removed functionality
  15. ^ "Creative ALchemy website". Archived from the original on 2008-12-17. Retrieved 2008-12-23.
  16. ^ IndirectSound
  17. ^ "DSOAL: A DirectSound DLL replacer that enables surround sound, HRTF, and EAX support via OpenAL Soft". GitHub. 20 April 2023.

External links

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