For decades, the G.711 codec was considered the gold standard of telephony, even though it suffers from the limitations of narrowband signal transmission.
Modern HD codecs, such as AMR-WB, EVS and Opus, typically feature several modes with different bit rates, sampling rates and coding schemes.
Some of these modes yield quality that is actually worse than G.711 and thus cannot be considered “high definition”. For example, the user experience provided by the AMR-WB mode with 6.6 kbit/s is well below toll quality.
Although, seven out of nine AMR-WB modes deliver a quality better than G.711, the claim of using an HD codec does not guarantee excellent user experience. Such codec mode changes can occur on a packet-by-packet basis without any indication in the SIP signaling.
Most VoIP monitoring tools on the market are not capable of detecting the codec based on analysis of the RTP payload.
Qrystal is a notable exception and provides voice service providers worldwide with accurate information on user satisfaction.