MLow: Meta’s low bitrate audio codec

This post introduces MLow, Meta's new low-bitrate audio codec designed to improve audio quality for users on slow network connections and low-end devices. MLow achieves two-times-better quality than Opus at 6kbps (POLQA MOS 1.89 vs 3.9) while maintaining 10% lower computational complexity. It utilizes a split-band encoding approach (low and high frequencies) and builds on classic CELP concepts with advancements in excitation generation, parameter quantization, and coding schemes. MLow also enables more effective Forward Error Correction (FEC) strategies, improving audio quality in packet loss scenarios. The codec has been fully launched on Instagram and Messenger calls and is rolling out on WhatsApp.