mSBC

mSBC, short for modified Sub-band Coding, is a speech codec used in Bluetooth to provide wideband speech over the SCO (Synchronous Connection-Oriented) links that carry the Hands-Free Profile (HFP) traffic. It was designed to replace the older CVSD codec to achieve greater intelligibility by delivering a wider audio bandwidth, typically extending the frequency response beyond traditional narrowband telephone speech.

The codec operates on a 16 kHz sampling rate and encodes speech into a compact bitstream suitable for the limited SCO bandwidth. It supports negotiated operation in which both ends indicate support; if both devices support mSBC, the link uses mSBC instead of CVSD; otherwise the session remains on CVSD. The result is clearer voice in hands-free calls, with better articulation and reduced listening fatigue in typical environments. mSBC is designed to be robust to Bluetooth link variability and packet loss while keeping latency low for real-time communication.

In practice, mSBC is implemented in many modern Bluetooth headsets, car hands-free systems, and mobile devices that support HFP 1.6 or later. It is primarily used for the Hands-Free and Headset profiles, not for audio streaming over A2DP. While it improves bandwidth efficiency over CVSD, it remains constrained by the Bluetooth SCO channel's bandwidth and power limits.

For compatibility, devices may fall back to CVSD if mSBC is not supported. The term mSBC is widely used in consumer devices and Bluetooth specifications to denote wideband speech capability within SCO-based links.