Windows Vista (formerly codenamed Windows "Longhorn") has many significant new features compared with previous Microsoft Windows versions, covering most aspects of the operating system.

In addition to the new user interface, security capabilities, and developer technologies, several major components of the core operating system were redesigned, most notably the audio, print, display, and networking subsystems; while the results of this work will be visible to software developers, end-users will only see what appear to be evolutionary changes in the user interface.

As part of the redesign of the networking architecture, IPv6 has been incorporated into the operating system, and a number of performance improvements have been introduced, such as TCP window scaling. Prior versions of Windows typically needed third-party wireless networking software to work properly; this is no longer the case with Windows Vista, as it includes comprehensive wireless networking support.

For graphics, Windows Vista introduces a new as well as major revisions to Direct3D. The new display driver model facilitates the new Desktop Window Manager, which provides the tearing-free desktop and special effects that are the cornerstones of the Windows Aero graphical user interface. The new display driver model is also able to offload rudimentary tasks to the GPU, allow users to install drivers without requiring a system reboot, and seamlessly recover from rare driver errors due to illegal application behavior.

At the core of the operating system, many improvements have been made to the memory manager, process scheduler, heap manager, and I/O scheduler. A Kernel Transaction Manager has been implemented that can be used by data persistence services to enable atomic transactions. The service is being used to give applications the ability to work with the file system and registry using atomic transaction operations.

Audio

Windows Vista features a completely re-written audio stack designed to provide low-latency 32-bit floating point audio, higher-quality digital signal processing, bit-for-bit sample level accuracy, up to 144 dB of dynamic range and new audio APIs created by a team including Steve Ball and Larry Osterman. The new audio stack runs at user level, thus reducing impact on system stability. Also, the new Universal Audio Architecture (UAA) model has been introduced, replacing WDM audio, which allows compliant audio hardware to automatically work under Windows without needing device drivers from the audio hardware vendor.

There are three major APIs in the Windows Vista audio architecture:

Windows Audio Session API – Very low-level API for rendering audio, render/capture audio streams, adjust volume etc. This API also provides low latency for audio professionals through WaveRT (wave real-time) port driver. Multimedia Device API – For enumerating and managing audio endpoints. Device Topology API – For discovering the internals of an audio card's topology.

Audio stack architecture

Applications communicate with the audio driver through Sessions, and these Sessions are programmed through the Windows Audio Session API (WASAPI). In general, WASAPI operates in two modes. In exclusive mode (also called DMA mode), unmixed audio streams are rendered directly to the audio adapter by an application, and no other application's audio will play, and signal processing has no effect. Exclusive mode is useful for applications that demand the least amount of intermediate processing of the audio data or those that want to output compressed audio data such as Dolby Digital, DTS or WMA Pro over S/PDIF, and exclusive mode is sometimes useful for Bit-Perfect music playback. WASAPI exclusive mode is similar to kernel streaming in function, but no kernel mode programming is required. In shared mode, audio streams are rendered by the application and applied per-stream audio effects known as Local Effects (LFX) (such as per-session volume control), then the streams are mixed by the global audio engine, where a set of Global Audio Effects (GFX) may be applied. Finally, they're rendered to the audio device.

After passing through WASAPI, all host-based audio processing, including custom audio processing, can take place. Host-based audio enhancement or sound effect processing modules are referred to as Audio Processing Objects, or APOs. All these components operate in user mode, only the audio driver runs in kernel mode. In exclusive mode, many APOs are bypassed; ASIO and OpenAL are not affected by APO.

The Windows Kernel Mixer (KMixer) is completely gone. The WASAPI mixer (audiodg.exe) is running in user mode. DirectSound and MME are emulated as Session instances rather than being directly connected to the audio driver. This does have the effect of preventing DirectSound from being hardware-accelerated, and completely removes support for DirectSound3D and EAX extensions, however APIs such as ASIO and OpenAL are not affected.

Audio performance

Windows Vista also includes a new Multimedia Class Scheduler Service (MMCSS) that allows multimedia applications to register their time-critical processing to run at an elevated thread priority, thus ensuring prioritized access to CPU resources for time-sensitive DSP processing and mixing tasks.

For audio professionals, a new WaveRT port driver has been introduced that strives to achieve real-time performance by using the multimedia class scheduler and supports audio applications that reduce the latency of audio streams. All the existing audio APIs have been re-plumbed and emulated to use these APIs internally, all audio goes through these three APIs, so that most applications "just work".

Issues A fault in the MME WaveIn/WaveOut emulation was introduced in Windows Vista: if sample rate conversion is needed, audible noise is sometimes introduced, such as when playing audio in a web browser that uses these APIs. This is because the internal resampler, which is no longer configurable, defaults to linear interpolation, which was the lowest-quality conversion mode that could be set in previous versions of Windows. The resampler can be set to a high-quality mode via a hotfix for Windows 7 and Windows Server 2008 R2 only.

Audio signal processing

New system built-in audio enhancement functionalities called system Audio Processing Objects (sAPOs) have been introduced, examples including Room Correction, Bass Management, Loudness Equalization and Speaker Fill. These adapt and modify an audio signal to take best advantage of the speaker configuration a given system has. Windows Vista also includes the ability to calibrate speakers to a given room's acoustics automatically, as well as setting speaker channels (stereo or more) and setting speaker types (full-range speaker or not), using a software wizard.

Windows Vista also includes the ability for audio drivers to include vendor audio effects, which are presented through user-mode Audio Processing Objects (APOs). These APOs are also reusable by third-party software. The APO can be either software-based (fake DSP) or hardware-based (access real hardware DSP). https://support.audient.com/hc/en-us/articles/27973407405844-Disabling-Windows-Audio-Enhancements

Audio devices support

Windows Vista builds on the Universal Audio Architecture, a new class driver definition that aims to reduce the need for third-party drivers, and to increase the overall stability and reliability of audio in Windows.

Support for Intel High Definition Audio devices (which replaces Intel's previous AC'97 audio hardware standard) Built-in passthrough support of padded AC-3, DTS, MP3, WMA and WMA Pro streams and outputting as S/PDIF or HDMI audio. Extended support for USB audio devices: Built-in passthrough support of padded AC-3, DTS, MP3, WMA and WMA Pro streams and outputting as S/PDIF. For 5.1 audio outputting as S/PDIF, Windows Vista itself does not include support for Dolby Digital Live and DTS Connect; it relied on vendor's audio drivers. Support for MIDI "Elements".See the USB Midi Devices 1.0 standard document for more information on MIDI Elements. New support for asynchronous endpoints.See section 3.3 of the USB Audio Devices 1.0 standard document for more information on endpoint types. IEEE 1394 (aka FireWire) audio support was slated for a future release of Windows Vista, to be implemented as a full class driver, automatically supporting IEEE 1394 AV/C audio devices. Support for audio jack sensing which can detect the audio devices that are plugged into the various audio jacks on a device and inform the user about their configuration. Endpoint Discovery and Abstraction: Audio devices are expressed in terms of audio endpoints such as microphones, speakers, headphones. For example, each recording input (Microphone, Line in etc.) is treated as a separate device, which allows recording from both at the same time. Support various LPCM audio channel configurations: mono sound, stereo sound (only 2.0 channels are supported), quad sound, 5.1 surround and 7.1 surround. Mandatory audio channel downmixing for LPCM audio streams in WASAPI shared mode (such as downmixing 5.1 LPCM audio streams to a 2.0 audio device); audio channel upmixing is depend on driver or firmware of audio devices.

Other audio enhancements A new set of user interface sounds have been introduced, including a new startup sound. The new sounds are intended to complement the Windows Aero graphical user interface, with the new startup sound consisting of two parallel melodies that are played in an intentional "Win-dows Vis-ta" rhythm. According to Jim Allchin, the new sounds are intended to be gentler and softer than the sounds used in previous versions of Windows. Microsoft engineer and musician Steve Ball created the user interface sounds, while the startup sound is a collaboration between three people: King Crimson's Robert Fripp composing the melody and soundscape, Tucker Martine creating the rhythm, and Ball handling the harmonization and orchestration. Ball also used Fripp and Martine's materials to create the new Windows Media Center startup sound. The new Volume Mixer displays a percentage value showing the current system volume while the volume level is being changed. Previous versions of Windows only displayed a volume meter. Windows Vista also allows controlling system-wide volume or volume of individual audio devices and individual applications separately. This feature can be used from the new Volume Control windows or programmatically using the overhauled audio API. Different sounds can be redirected to different audio devices as well. Windows Vista includes integrated microphone array support which is intended to increase the accuracy of the speech recognition feature and allow a user to connect multiple microphones to a system so that the inputs can be combined into a single, higher-quality source. Microsoft has also included a new high quality voice capture DirectX Media Object (DMO) as part of DirectShow that allows voice capture applications such as instant messengers and speech recognition applications to apply Acoustic Echo Cancellation and microphone array processing to speech signals.

Speech recognition

Windows Vista is the first Windows operating system to include fully integrated support for speech recognition. Under Windows 2000 and XP, Speech Recognition was installed with Office 2003, or was included in Windows XP Tablet PC Edition.

A brief speech-driven tutorial is included to help familiarize a user with speech recognition commands. Training could also be completed to improve the accuracy of speech recognition.

Windows Vista includes speech recognition for 8 languages at release time: English (U.S. and British), Spanish, German, French, Japanese and Chinese (traditional and simplified). Support for additional languages is planned for post-release.

Speech recognition in Vista utilizes version 5.3 of the Microsoft Speech APIWindows Vista, SAPI