Based on 56k’s answer : https://askubuntu.com/questions/676853/bluetooth-headset-with-poor-sound-quality-on-ubuntu
1 sudo nano /etc/bluetooth/main.conf
Add to head of the file
Find MultiProfile in the document and set it multiple
MultiProfile = multiple
After this restart bluetooth when the quality is become bad with service restart. (Mostly one time per connection)
1 sudo systemctl restart bluetooth
Bluetooth devices which has microphone uses two channel to provide output and input in the same time. When one channel is used for microphone the other channel is not enough to provide stereo output so output becomes bad. You can select microphone + mono output or only stereo output. The selection in linux is little bit hard and mostly microphone + mono is selected and the most GUIs’s mode selecting windows is not working correctly.