AES San Francisco’s June meeting was titled “Understanding Audio in HDMI.” Dr. Tom Kite gave an overview of HDMI (high-definition multimedia interface). The meeting was held at Cogswell College, in California’s Silicon Valley. Fifty people attended.

Dr. Kite is Director of Engineering for Audio Precision, in Beaverton, Oregon.

HDMI is a single cable connection scheme for audio, video, and multimedia devices. Connectors and cables are similar to those used for USB (universal serial bus), in both appearance and function. Connectors have nineteen pins, and are hot pluggable, meaning that devices can be connected and disconnected while in operation.

HDMI is rapidly becoming the industry standard for transmitting audio and video data streams, for consumer and ‘prosumer’ (between consumer and professional) devices. It replaces a long list of analog wired interfaces, such as S-video, composite video, and audio shielded cables.

Devices equipped with HDMI, such as Blu-ray disc players, digital televisions, HDTV (high definition television), camcorders, and consumer audio amplifiers, can be interconnected quickly and easily.
HDMI is capable of carrying very high bit rate audio, including multi-channel PCM at up to 192 kHz sample rates, Dolby TrueHD, and DTS HD Master Audio. These have bit rates in the tens of megabits per second.

HDMI also allows interfacing of all audio/video controls, including hand-held remotes. Functions like play and record, timer programming, audio controls, and auto source switching can be passed between devices.

Multi-media devices vary greatly, with differing video frame rates and color spaces, number of audio channels, and types of audio compression formats. HDMI incorporates a two-way data stream called EEDID (enhanced extended display identification), between source and sink, that ensures compatibility between the two.

Dr. Kite demonstrated an HDMI analyzer, which tests its full range of capabilities, using a simple, easy-to-read UI (user interface).

by Paul Howard