How to enable G.722 codec for Azure Communication Services phone number?

Hi @Raife Hizlan
Azure Communication Services (ACS) does not currently allow enabling or forcing the G.722 wideband codec for Microsoft-managed (PSTN) phone numbers. When you use an ACS phone number, calls are routed through the public switched telephone network, which is inherently narrowband and limited to G.711 (8 kHz), and ACS automatically handles codec negotiation without exposing any configuration to override this behavior. As a result, lower speech recognition accuracy especially for numbers is expected due to the limited audio quality. G.722 (16 kHz wideband) is only used in VoIP scenarios (ACS SDK clients) or in Direct Routing setups where you control a Session Border Controller (SBC) and can influence codec negotiation. Therefore, if wideband audio is required for better AI speech recognition, you must either use VoIP-based calling or implement Direct Routing, as it is not supported with standard ACS phone numbers.
https://dori-uw-1.kuma-moon.com/en-us/dynamics365/customer-service/administer/voice-channel-faqs?wt.mc_id=knowledgesearch_inproduct_azure-cxp-community-insider#setup
https://dori-uw-1.kuma-moon.com/en-us/azure/communication-services/concepts/telephony/direct-routing-infrastructure
https://dori-uw-1.kuma-moon.com/en-us/azure/communication-services/concepts/voice-video-calling/calling-sdk-features
Let me know if you have any further assistance needed.

G.722 use depends on which leg of the call is being considered and how the PSTN connectivity is set up.

For Azure Communication Services (ACS) telephony:

1. Codec support on ACS Direct Routing (SBC ↔ ACS media processor)
   For ACS Direct Routing, the leg between the Session Border Controller (SBC) and the ACS Cloud Media Processor supports:
   • SILK
   • G.711
   • G.722
   • G.729
     The SBC can be configured to prefer or force G.722 by excluding other codecs from the offer:
   • Configure the SBC so that SDP offers toward ACS include only G.722 (or prioritize it) if wideband audio is desired.
   • This gives 16 kHz wideband audio on the SBC ↔ ACS media leg.
2. Codec on ACS Calling SDK app ↔ ACS media processor
   On the leg between the ACS Calling SDK app and the Cloud Media Processor, ACS uses:
   • G.722
     This is fixed today; work on adding more codecs is in progress. So if the AI voice assistant is built using the ACS Calling SDK, that leg already uses G.722.
3. Microsoft-managed phone numbers vs Direct Routing
   The context provided describes codec control explicitly only for Direct Routing scenarios (SBC ↔ Cloud Media Processor). It does not expose a setting to change codecs per Microsoft-managed phone number directly in the portal or via number configuration.
   To explicitly control and guarantee G.722 on the PSTN side, Direct Routing with a certified SBC is required, where the SBC is configured to offer G.722.
4. Implications for speech recognition with Azure OpenAI Realtime API
   • If PSTN → ACS is narrowband (G.711) but ACS → AI assistant is wideband (G.722 / 16 kHz), recognition quality is still limited by the narrowband leg.
   • To improve recognition (especially for numbers), ensure the PSTN leg into ACS is wideband by using Direct Routing and configuring the SBC for G.722.

Summary:

• G.722 is supported on ACS media legs (SBC ↔ Cloud Media Processor and Calling SDK ↔ Cloud Media Processor).
• There is no per-phone-number setting in the provided context to switch Microsoft-managed numbers from G.711 to G.722.
• To explicitly enable and control G.722 for PSTN calls, Direct Routing with a certified SBC is needed, with the SBC configured to prefer or enforce G.722.

References:

• Azure direct routing infrastructure requirements
• Plan Direct Routing
• Number types
• Use the GPT Realtime API via WebRTC