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Tech Notes

Codec Compatibility for Comrex Codecs working on ISDN and other Digital Circuits

There are two main factors when determining inter-operability among different makes and models of digital audio codecs. First, the codecs must use the same coding algorithm and the implementation must follow the standards for that algorithm. Second, for codecs used at data transmission rates higher than a single 56 or 64 kb/s channel, the method used for channel aggregation must be compatible. The process of stacking up channels is referred to as Inverse Multiplexing (or IMUX).

The Comrex codecs designed for ISDN and other digital circuits employ G.722, ISO/MPEG Layer II and/or ISO/MPEG Layer III algorithms. Our implementation carefully follows the standards for these algorithms, and our codecs work with other manufacturers who follow these standards. The enhanced TURBO G.722 that provides low delay 15 kHz audio is a proprietary implementation and will work only with other Comrex codecs at the 112/128 kb/s rate.

The Comrex DX-200 MPEG Layer II codec provides three IMUX alternatives for wide compatibility: The "CCS IMUX mode" allows operation with all codecs manufactured by MUSICAM ® USA and with Telos Zephyr ® codecs in its MPEG Layer II mode. The "RE IMUX mode" provides compatibility with the RE Model 661/662 codecs. With the IMUX out, it is also possible to use BONDING terminal adapters to aggregate channels externally.

Model	Algorithms	Compatibility
Matrix with ISDN Module	* ISO/MPEG Layer III * G.722 * Turbo	Other Layer III codecs such as the Telos Zephyr ® and MUSICAM Prima ® - in mono mode only. Any G.722 codec. * Any Comrex codec set for Turbo
Envoy Nexus DXR.1 DXP.1	* G.722 * Turbo	* Any G.722 Codec * Any Comrex Codec set for Turbo