I've encoded audio books with Opus at 32 kbps and they sound good. I wouldn't vouch for music at such a low bitrate, but it's nice to have a set of 14 CDs only

I've encoded audio books with Opus at 32 kbps and they sound good. I wouldn't vouch for music at such a low bitrate, but it's nice to have a set of 14 CDs only take up a quarter gigabyte on an SD card.