From Digital Interface Handbook, Third Edition

4.9 Data-Reduced Audio Over Standard Two-Channel Interfaces

4.9.1 General Principles

The standard two-channel interface was originally designed for linear PCM audio samples but in recent years there has been increasing use of data-reduced audio coding systems such as Dolby Digital (AC-3), DTS and MPEG. Because consumer systems in particular needed the ability to transfer such signals digitally, the non-audio mode of the interface has been adapted to the purpose. This is described in a relatively new IEC standard numbered 6193731. In addition to a general specification detailing the principles it also has a number of parts that describe the handling of specific data-reduced audio formats, some of which are not yet finalized at the time of writing. A similar but not identical SMPTE standard (337M)32 describes professional non-audio applications of the interface, including its use for carrying Dolby E data (see below). SMPTE 338M and 339M specify data types to be used with this standard. The SMPTE standard is also more generic than the IEC standard, designed to deal with a variety of data uses of the interface, not just low-bit rate audio. It can also carry time-stamp data in the form of SMPTE 12M timecode. The reader is referred to the standards for more precise details regarding implementation of specific formats.

In both SMPTE and IEC versions the low-bit rate audio data is carried in bursts in place of the normal linear PCM audio information, with bit 1 of channel status set to the 'other uses' or 'non-audio' state.

Products & Services
Digital Audio Systems
Digital audio systems electronically record and store audio signals such as voice, music, alarm, and security messaging for broadcast, editing, monitoring, and playback.
Audio Analyzers
Audio analyzers measure the noise and audio spectrum of output from an amplifier or a stereo.
Motor Controllers
Motor controllers receive supply voltages and provide signals to motor drives that are interfaced to motors. They include a power supply, amplifier, user interface, and position control circuitry.
Voice Loggers and Audio Recorders
Audio recorders / voice loggers are used to locate, retrieve, duplicate and/or distribute audio voice or data information from single system environments to large multi-channel networked systems.
FireWire® Products
FireWireregistered: . products use an interface standard developed by Apple Computer and adopted by the IEEE for very fast digital data transfers. FireWire, a registered trademark of Apple Computer, is a communications protocol for the transmission of data, video, and audio over a single cable at very high bit rates.

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