DMR Overview

DMR is a digital two way radio standard that provides voice and data transfer.
The DMR standard was created by the European Telecommunications Standards Institute (ETSI), and the standard includes three tiers:

• Tier 1: Licence Free, within the PMR446 allocation, 500mW ERP output power, and without infrastructure (no repeaters) 

• Tier 2: Licenced conventional, PMR bands from 66 to 960MHz, Time Division Multiple Access (TDMA) with two timeslots

• Tier 3: Licenced trunking, PMR bands from 66 to 960MHz, Time Division Multiple Access (TDMA) with two timeslots

The ETSI DMR standard does not specify a vocoder, so manufacturers have always been free to choose thier own vocoder. This could have resulted in a lack of interoperability between manufacturers equipment, so manufacturers signed up to a memorandum of understanding in 2005, where one of the agreements was to use the AMBE vocoder by DVSI.

Audio picked up by a microphone is converted into a digital bitstream using the AMBE+2 vocoder, which is part of a range of speech compression products offered by Digital Voice Systems, Inc. (DVSI) .
AMBE stands for Advanced Multi-Band Excitation, with AMBE+2 being an enhanced version of DVSI's AMBE vocoder.