 To ensure compatibility, 3GPP demand at least AMR-NB codec (narrow band), but the recommended speech codec for VoLTE is Adaptive Multi-Rate Wideband (AMR-WB), also known as HD Voice.This codec is mandated in 3GPP networks that support 16 kHz sampling.Volte
Fraunhofer IIS has proposed and demonstrated "Full-HD Voice", an implementation of the AAC-ELD (Advanced Audio CodingEnhanced Low Delay) codec for LTE handsets.