When we hear about this problem, it often has to do with mute being stuck on, frequently on an iPad 2, early iPad Mini, early iPhone.
- Are other apps on the device able to make sound?
- Is the mute switch set to make sound? On early devices this is a physical switch, on later devices this is an option in control center (vertical slide up to raise control center).
- Have you tried quitting GeoShred and relaunching it?
- Have you tried booting the device.
- If the device is an iPad 2, it's very common for the mute to get stuck on, because the same switch is used for mute or auto-rotate lock. Here is an article on how folks solve the "iPad 2 Mute Stuck On" problem: https://discussions.apple.com/thread/5646575