The Tech Blog

This bit of tech was one of the most key innovations which made Bluetooth audio good. Classic Bluetooth audio sounded OK, but drained battery quickly and sometimes lagged behind video. Bluetooth Low Energy (BLE) solved power issues, but wasn’t originally built for audio. Early BLE couldn’t ensure packets arrived exactly when needed, leading to dropouts, delays, or distorted sound. We needed a reliable, low-latency audio without sacrificing battery life. That’s why Bluetooth LE Audio was introduced along with BLE v5.2 spec.

Think of Isochronous Adaptation Layer(ISOAL) as the invisible worker organizing audio packets to ensure they’re delivered precisely on time. It acts as a bridge between your audio source, like a smartphone, and the wireless radio inside your headphones/earbuds.

Before ISOAL existed, audio streams had to cram large chunks into single packets, causing inflexibility and interruptions. Synchronizing stereo earbuds was difficult because packets weren’t always perfectly timed. ISOAL fixes these issues, enabling smooth stereo playback and synchronized sound across multiple devices without lag or glitches.

So how does it actually work? When your phone streams audio, it hands complete chunks (called Service Data Units, or SDUs) to ISOAL. If these chunks are too large for transmission, ISOAL breaks them into smaller pieces. It labels each smaller piece (called Protocol Data Units, or PDUs) with precise timestamps and sequence numbers. These labels act as detailed instructions, so your earbuds know exactly when to reconstruct and play the audio smoothly.

In summary, ISOAL ensures perfect audio sync between left and right earbuds. BTW, ISOAL is implemented entirely in the controller’s firmware and doesn’t need any additional hardware or app firmware coding. Its timestamps are in the microsecond range, ensuring precision. ISOAL handles both Connected Isochronous Streams (CIS) for point-to-point audio (true-wireless earbuds) and Broadcast Isochronous Streams (BIS) for one-to-many audio.