The iOS 12.2 software makes a significant improvement over the previous audio quality in iOS 12.1.4, resulting in audio messages that sound a lot better and crisper.
Audio messages sent via the Messages app through the iMessage protocol used to be encoded with the ARM coded at 8000 Hz, but iOS 12.2 improves audio messaging quality by switching to new Opus codec at 24000 Hz.
The same codec is also being used by the desktop Messages app on the macOS Mojave 10.14.4 software. As a result of the new codec and the three times higher sound resolution, your audio messaging will get a significant boost in the quality department once Apple releases the OS updates.
Listen the audio for yourself right below.
MacRumors says that the Opus codec at 24000 Hz produces larger file sizes due to increased audio resolution making the audio sound much crisper, clearer and louder than before.
Right now, to hear the improved audio quality, audio messages need to be sent from a device running iOS 12.2 to a device running iOS 12.2 (or a Mac running macOS Mojave 10.14.4). An audio message sent to a device running iOS 12.1.4 uses the original .AMR file format and not the improved .CAF file format.
The slight file size increase shouldn’t be any cause for concern from a storage perspective because the Messages app by default removes all audio messages from the device two minutes.
To keep your audio messages forever, go to Settings → Messages, tap Expire underneath the Audio Messages hading and choose Never.