This is the official quality for YouTube Music whether you’re on a mobile network or Wi-Fi.
Always high: 256 kbps AAC (maintains this even when the connection is poor).
High: 256kbps AAC (highest quality setting).
You can choose between a few different sound quality settings: When the service was first announced there wasn’t any official documentation of sound quality but that has since been added to the YouTube Music help page. You can’t actually create a custom EQ for YouTube Music though. For instance, the Samsung Galaxy S10e allows you to toggle Dolby Atmos and choose between a few dubious EQ presets. There is an EQ option under settings, but it relies on your phone’s sound quality options. Unlike other streaming platforms, audio adjustments are restrictive.