DMR digital voice

A digital two-way radio standard that carries two conversations at once on one channel.

ModeDMR digital voice

FamilyDigital voice

Audio exampleComing

DMR sounds like a rough, raspy digital buzz with a fast pulsing edge, often described as 'angry bees', lasting as long as the person is talking.

What does it sound like?

Plate 12Digital voice

A raspy, buzzing sound with a pulsing edge, like angry bees.

Field marksTwo conversations share one channel, taking turns4-level FSK, 4,800 symbols per second12.5 kHz channels

Who uses it?

Businesses, some public agencies, and hams (with worldwide networks of linked repeaters).

Where and when can I hear it?

VHF and UHF, including ham repeaters around 144-148 and 420-450 MHz.

The science

DMR squeezes two separate conversations into one 12.5 kHz channel by taking turns very quickly: time is cut into 30-millisecond slots, and two slots alternate inside a 60-millisecond frame (a scheme called two-slot TDMA, time division multiple access). Each burst is sent with four-level frequency shift keying (4FSK), where the carrier jumps among four frequencies, each standing for two bits, at 4,800 symbols per second for 9,600 bits per second. Speech is squeezed by the AMBE+2 vocoder, a speech coder that sends a compact description of the voice at 3.6 kbps rather than the sound wave itself, and error-correcting codes such as Golay and Reed-Solomon protect the data.

Why use it?

Because each radio transmits only half the time, one repeater and one channel can carry two talk paths, which a 2016 fact sheet from the US Department of Homeland Security's Office of Emergency Communications (now part of CISA) describes as 6.25 kHz-equivalent spectral efficiency, alongside improved power performance. DMR radios can also run ordinary analog FM, which makes a gradual move from older analog systems easier, and the standard adds messaging and data services that analog radio lacks.

Lore

ETSI first ratified the DMR standard in 2005. It comes in tiers: Tier I is a low-power, license-free version for the 446 MHz band, while Tiers II and III cover licensed conventional and trunked systems.

What do the decoded parts mean?

Talkgroup: The group being called, similar to a channel within a network.
Radio ID: A number identifying the transmitting radio.

Easily confused with

P25 digital voice: P25 is a steadier buzz without the pulsing turns
NXDN digital voice: NXDN often uses narrower channels

How to recognize it

DMR (Digital Mobile Radio) packs two conversations onto one 12.5 kHz channel by taking turns in 30-millisecond time slots. A single handheld radio transmits only in its own slot, so its signal switches on and off about 17 times a second, which gives the buzz its characteristic flutter. A repeater, by contrast, transmits continuously in both slots and sounds like a smoother, steadier buzz.

The data rate is 9,600 bits per second using four-level frequency-shift keying. You will never hear speech directly; the voice is compressed digitally and only a compatible radio or decoding software can turn it back into sound.

Easily confused with:

P25 Phase 1: a similar gravelly buzz, but continuous with no time-slot flutter.
NXDN and dPMR: digital voice systems, often on narrower channels, that sound thinner and less pulsed.
TETRA (mainly outside North America): a wider, louder, more mechanical buzz.

Where and when to hear it

DMR is common on business and industrial radio channels in the VHF and UHF bands (roughly 136-174 and 400-512 MHz): factories, hotels, transit, utilities and campus security. Some public agencies use it too.

Radio amateurs use it widely on repeaters in the 2-meter and 70-centimeter ham bands, linked through worldwide networks such as BrandMeister. Ham DMR traffic is organized by talkgroups (numbered virtual channels) and each ham operator registers a numeric ID (through RadioID.net) and programs it into the radio, so a local repeater can carry a conversation with someone on another continent.

A little history

DMR was standardized by the European Telecommunications Standards Institute (ETSI) in 2005 as an open standard for professional mobile radio, with the aim of moving businesses from analog FM to digital while fitting twice as many users into the same spectrum. Manufacturers built compatible radios, and Motorola's MOTOTRBO line, launched in 2007, helped make DMR one of the most widely deployed digital two-way systems in the world.

The standard defines three tiers: Tier I for simple license-free radios, Tier II for conventional two-slot systems, and Tier III for trunked systems, where radios are assigned channels automatically.

Common questions

Is it legal to listen to DMR?

Rules depend on the country. In the United States, federal law generally allows receiving radio communications that are readily accessible to the public, while some states restrict scanners in vehicles or using what you hear for certain purposes. Some countries are stricter and allow listening only to transmissions meant for general reception, such as broadcasts, amateur and CB radio, and weather and navigation services. Amateur DMR is open to anyone to receive. Encrypted DMR traffic is not meant to be read, and nothing here suggests trying.

Why does DMR sound like buzzing instead of voices?

The voice is converted to compressed digital data before transmission. A receiver has to demodulate the data and run it through the matching voice decoder to recover speech; an ordinary FM radio just plays the raw data as a buzz.

Can I listen to ham DMR conversations?

Yes. Amateur DMR is unencrypted by rule in the US (47 CFR 97.113) and in most other countries, and many networks also stream talkgroups online. Free software such as SDRTrunk can decode unencrypted DMR from a software-defined radio.

Is DMR encrypted?

Ham DMR is not. Business and public-agency users can enable encryption; when they do, listeners can't read the traffic, and decrypting it without authorization is illegal.