From There to Hear: Audio Over IP
Barix is a well-known name in IP codecs. Many are familiar with the Instreamer/Exstreamer pairs, but the company also makes codecs, such as the Exstreamer 500. This device comes with balanced analog inputs and outputs, 4 GPIO inputs and outputs, as well as a USB port for audio fail-over from a storage device. Algorithms available are MP3 (variable bit rate, between 8 and 320kb/s, and sample rates between 8 and 48kHz), PCM, and AAC-LC, HE-AAC, and HE-AAC v2.
Another brand of IP codecs that sees some use is AEQ. It makes several different units, but we'll look at the Phoenix Venus. This is a 1RU, full-duplex codec that will handle two stereo pairs (or four mono) simultaneously. The two AES ins/outs are available on DB15 connectors, with SRC, and will individually sync between 16 and 96kHz. Analog ins/outs are available via XLR connectors. The unit has a single 10/100baseT Ethernet (RJ-45) port.
Phoenix Venus was designed to meet the N/ACIP EBU Tech3326 standard and includes the option of an adaptive buffer in order to absorb network jitter; DHCP allowing the automatic configuration of the IP Network parameters; and FEC and automatic reference clock adjustment in order to synchronize both ends of the communications link. Audio algorithms include G.711, G.722, PCM, MP2, and optionally AAC-LC and AAC-LD. The unit also includes AEQ-LD, which is AEQ's proprietary codec.
The delivery of audio from point A to point B via IP, whether over your LAN, a WAN, or the Internet, has become commonplace nowadays. While it may not be imminent, the demise of ISDN is certainly on the horizon, so now is the time (if you haven't already) to learn something about audio over IP.
Irwin is RF engineer/project manager for Clear Channel Los Angeles. Contact him at firstname.lastname@example.org.
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