 | This article has multiple issues. Please helpimprove it or discuss these issues on thetalk page.(Learn how and when to remove these messages) (Learn how and when to remove this message)
|
Multi-Band Excitation (MBE) is a series of proprietaryspeech 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 asImproved Multi-Band Excitation (IMBE),Advanced Multiband Excitation (AMBE), AMBE+ and AMBE+2 are based on this MBE method.
AMBE is acodebook-basedvocoder that operates atbitrates 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[citation needed] offorward 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 theInmarsat andIridiumsatellite telephony systems and certain channels onXM Satellite Radio and is thespeech coder forOpenSkyTrunked radio systems.
AMBE is used inD-STARamateur radio digital voice communications. It has met criticism from the amateur radio community because the nature of itspatent[1] and licensing runs counter to the openness of amateur radio, as well as usage restriction for being "undisclosed digital code" underFCC rule 97.309(b) and similar national legislation.[2]
System Fusion, open specification fromYaesu, also uses AMBE codec withC4FM modulation.
TheNXDN 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 older Phase 1 radios such as theMotorola XTL and XTS series use the earlier IMBE codec. Newer Phase 1 capable radios such as the APX series radios use the AMBE+2 codec, which is backwards compatible with Phase 1.
Digital Mobile Radio (DMR) and Motorola's MOTOTRBO use the AMBE+2 codec.
Use of the AMBE standard requires a license from Digital Voice Systems, Inc. While a licensing fee is due for most codecs, DVSI does not disclose software licensing terms. Anecdotal evidence[citation needed] suggests that licensing fee begin from between $100,000 to $1 million. For purposes of comparison, licensing fees for use of theMP3 standard started at $15,000. For small-scale use and prototyping, the only option is to purchase a dedicated hardware IC from DVSI. These ICs can be purchased for less than $100 in small quantities.[3]
DSP Innovations Inc. offers a software implementation of APCO P25 Phase 1 (Full-Rate) and Phase 2 (Half-Rate) codecs as well as DMR and dPMR codecs. A technology licence from DVSI is required.The patent for IMBE has expired.
Codec2 is an open source alternative which uses half of the bandwidth of AMBE to encode speech of similar quality,[4] created by David Rowe and lobbied byBruce Perens. Codec2 still continues to evolve, with additional "modes" being developed, refined and made available on a continuous basis. This has resulted in an open source codec that has progressively increased its robustness and performance – when subjected to some of the most challenging RF and acoustic environments.[5]
