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 used to be encoded with the ARM codec at 8000 Hz, but iOS 12.2 boosts audio quality by switching to a new Opus codec at 24000 Hz.
The same codec is also used in Messages on macOS Mojave 10.14.4.
As a result of the new codec with three times higher frequency resolution, your audio messaging will get a significant boost in the quality department once these updates drop.
Have a listen right below.
MacRumors says that the Opus codec at 24000 Hz produces larger file sizes due to increased audio resolution, but you get a much crisper, clearer and louder sound 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 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 after two minutes.
To keep your audio messages forever, go to Settings → Messages, then tap Expire underneath the Audio Messages heading and choose the option labeled with the text Never.