Multi-Band Excitation

Multi-Band Excitation (MBE) is a series of proprietary speech coding standards developed by Digital Voice Systems, Inc. (DVSI). In 1967 Osamu Fujimura (MIT) showed basic advantages of the multi-band representation of speech ('An Approximation to Voice Aperiodicity', IEEE 1968). This work gave a start to development of the 'multi-band excitation' method of speech coding, that was patented in 1997 (now expired) by founders of DVSI as 'Multi-Band Excitation' (MBE). All consequent improvements known as Improved Multi-Band Excitation (IMBE), Advanced Multiband Excitation (AMBE), AMBE+ and AMBE+2 are based on this MBE method. AMBE is a codebook-based vocoder that operates at bitrates of between 2 and 9.6 kbit/s, and at a sampling rate of 8 kHz in 20-ms frames. The audio data is usually combined with up to 7 bit/s of forward error correction data, producing a total RF bandwidth of approximately 2,250 Hz (compared to 2,700–3,000 Hz for an analogue single sideband transmission). Lost frames can be masked by using the parameters of the previous frame to fill in the gap. AMBE is used by the Inmarsat and Iridium satellite telephony systems and certain channels on XM Satellite Radio and is the speech coder for OpenSky Trunked radio systems. AMBE is used in D-STAR amateur radio digital voice communications. It has met criticism from the amateur radio community because the nature of its patent and licensing runs counter to the openness of amateur radio, as well as usage restriction for being 'undisclosed digital code' under FCC rule 97.309(b) and similar national legislation. The NXDN digital voice and data protocol uses the AMBE+2 codec. NXDN is implemented by Icom in the IDAS system and by Kenwood as NEXEDGE. APCO Project 25 Phase 2 trunked radio systems also use the AMBE+2 codec, while Phase 1 radios use the earlier IMBE codec. Digital Mobile Radio (DMR) and Motorola's MOTOTRBO use the AMBE+2 codec.