Core Audio in Mac OS X Tiger to improve audio handling

Sources close to Apple say that the new version of Core Audio will introduce two new audio units, aggregate device support, nonnative audio file format support, and other tools that let developers perform live mixing and playback of audio content.

New Audio Units

Tiger's version of Core Audio will present two new audio units that developers can use in their applications.

A file-playback audio unit will make it possible for applications to use an existing sound file as an input source. The audio unit will convert file data from any format to linear PCM so that it can be processed by other audio units, sources said. Linear PCM (LPCM) is an uncompressed audio format that is similar to CD audio, but with higher sampling frequencies and quantisations. The format offers up to 8 channels of 48kHz or 96kHz sampling frequency and 16, 20 or 24 bits per sample but not all at the same time.

The second audio unit will handle time and pitch transformation modifications to audio data. Developers will be able to use this audio unit to change the playback speed without changing the pitch, or vise versa.

Aggregate Device Support

Tiger's version of Core Audio will also support the creation of aggregate devices, sources said, allowing developers to combine multiple audio devices together under the auspices of a single audio device. For example, developers can take two devices with two input channels each, combine them to create a single aggregate device with four input channels, and then let Core Audio take care of routing the audio data to the appropriate hardware device.

Nonnative Audio File Format Support

Another planned enhancement to Core Audio is an extension mechanism for supporting audio file formats not natively supported by Core Audio in Mac OS X. This mechanism will reportedly allow developers to create components for reading and writing these audio file formats, while an updated API will aid applications in detecting and utilizing the custom components.

Two New APIs

Tipsters also said that Core Audio will add two new APIs to its toolbox.

A new extended audio file API will ease the complexity previously associated with converting files from one format to another. The API will read data in any format supported by Core Audio and then convert it to and from linear PCM format.

Meanwhile, a new clock API will allow developers to create and track MIDI time formats. The API will reportedly support the use of the MIDI Time Code (MTC) and MIDI Beat Clock protocols to synchronize operations between MIDI-based controllers.

Developer Tools

Finally, sources expect Tiger to ship with a new Audio Unit Lab tool, which will let developers graphically host audio units and examine the results. The tool will reportedly host audio units and allow developers to use them to do live mixing and playback of audio content.

In recent weeks AppleInsider has provided extensive coverage of Mac OS X 10.4 Tiger. Previous reports include coverage of Tiger's Spotlight search, Safari with RSS, Mail 2.0 with smart mailboxes, iCal 1.5.3, Resolution Independent UI and 256x256 Icons, AppleScript 1.10, Installer 2.0, web enabled Help, Fast Logout, Access Control Lists, OpenGL enhancements, adoption of OpenAL, Core Data, PDF Kit, SQLite, and networking-related enhancements.