The Sound::setDefaults documentation says:
frequency
Default playback frequency.
- Units: Hertz
- Default: 48000
But the default frequency appears to be dependent upon the sample rate of the loaded sound, so if you use 48000 as the default value the pitch of your sounds may be incorrect.
Someone aiming only to set the default priority of a sound probably needs to call Sound::getDefaults first to get the current frequency and preserve it, it might make sense to call that out in the docs.