I don't know, but feel free to try the following.
1. Try rebooting your iPad.
2. Make sure that the mute switch isn't on on the side of the device.
3. Make sure the volume level is raised.
4. Make sure you're not covering the mic on the iPad.
5. If using a third-party recording app, make sure you have a version that supports iOS 7.
6. As a last resort, restore your device and set it up as new.