If you have no sound on Rhythm Cat, Treble Cat, Bass Cat or Ear Cat, you may have accidentally muted your device. Even if your volume is turned up and you’re still able to get sound through headphones or core apps such as Youtube.
iPad:

For older iPad Devices
Go to Settings – General – under ‘Use Side Switch’ make sure ‘Mute’ is selected and not ‘Lock Rotation’

iPhone:
Check the side switch on your phone is not set to silent mode.

Otherwise, check that you are not connected to headphones via Bluetooth.
If you are still having trouble with sound please contact us.