Field Guide · technology

Also known as: IMBE

IMBE (Improved Multi-Band Excitation) is the vocoder of P25 Phase 1, part of the MBE codec family from DVSI.1

VVUVU each band marked voiced (V) or unvoiced (U)
IMBE (used by P25 Phase 1) is a multi-band excitation codec that labels each spectral band voiced or unvoiced.

How it works

IMBE runs at about 7.2 kbps over the air, of which roughly 4.4 kbps is voice and the rest is forward error correction protecting the parameters — important because a corrupted parameter sounds far worse than a corrupted audio sample.

Relevance to SDR

GopherTrunk decodes IMBE frames from P25 Phase 1 and synthesises audio. Its successor, AMBE+2, is used by newer systems.

Sources

  1. Multi-Band Excitation — Wikipedia, on the MBE vocoder family that includes IMBE. ↩

See also

Learn it step by step

From the blog