# No sound on calls (SIP Device, IP Phone, or Softphone)
## Overview
Having a call come through, and hearing no audio (or worse, the other party hearing no audio!) can be incredibly frustrating. This guide aims to cover common causes for no-audio issues.
## Codecs
Crazytel recommends G.711a as the primary Codec on calls, as it is the most common codec used by Telcos in Australia. Although other Codecs are allowed (G729a/b, PCMA, and PCMU), Crazytel officially supports G711a as it is a widely supported codec that requires minimal encoding/decoding time, whilst retaining clarity and minimizing distortion.
## So how do I change Codecs?
Changing codecs varies greatly between SIP devices. Codec settings can generally be found under sections like 'Audio Settings', 'Voice Settings', 'Codec Preferences', or 'Network settings'.
For device-specific instructions, we recommend using your preferred search engine to search for the admin manual for your device.
If you're having trouble locating the manual, feel free to reach out to our support team for assistance!