AMR-WB / G.722.2
AMR-WB is mandatory for VoLTE — every LTE voice call uses it. Understanding rate adaptation and the AMR payload format (RFC 4867) is essential for mobile VoIP and operator codec policy.
What It Defines
Adaptive Multi-Rate Wideband (AMR-WB) is the mandatory codec for HD voice over LTE (VoLTE) and UMTS. Operates at 9 bitrates from 6.6 to 23.85 kbps with adaptive rate switching. Also standardized as G.722.2 by ITU-T. AMR-NB (narrowband) covers 4.75–12.2 kbps for GSM fallback.
Canonical (Normative)
Related References
The global collaboration of telecommunications standards bodies that produces the mobile network specifications: GSM/EDGE, UMTS/HSPA, LTE/4G, 5G NR, and IMS. Technical specifications (TS) and reports (TR) are freely available at 3gpp.org. Releases (Rel-8, Rel-15, Rel-17…) provide versioned capability sets.
Related Specs
RTP carries all real-time media: VoIP, WebRTC, live video, and video conferencing. Understanding SSRC demultiplexing, jitter buffers, and RTCP feedback loops is essential for any media application.
LTE is the dominant global mobile network. VoLTE, QoS bearers, and EPC architecture are directly relevant when building mobile-connected applications, IoT modules, or carrier infrastructure.
G.722 is the standard for HD voice in SIP and enterprise telephony. When you enable 'HD Voice' on a SIP trunk, G.722 is typically what's negotiated. Essential for enterprise UC deployments.
Opus is the codec for real-time audio on the internet. WebRTC mandates it; Discord, Zoom, and most VoIP apps use it. Understanding bitrate, FEC, and frame sizing directly impacts audio quality and bandwidth.
AMR-NB is the fallback voice codec for pre-VoLTE mobile networks and many carrier voicemail systems. The `#!AMR` file header and RFC 4867 RTP framing are distinct from AMR-WB.
The AMR file header is a minimal envelope pattern — one magic line then framed payloads. Required when parsing `.amr`/`.awb` attachments from carrier APIs or MMS gateways.
VoLTE and IMS carry AMR over RTP per RFC 4867 — not as `.amr` files. CMR bits and octet-align vs bandwidth-efficient modes cause real interoperability bugs between carriers.