Your iPad has multiple microphones - each being used with different Apps.
Have you placed the iPad in a fitted case? Some third party cases may obstruct one or more of the iPad’s microphones. If the iPad is in a case, remove it - and then test with the Apps causing difficulties.
Similarly, have you fitted a screen protector? Some models of iPad have a forward-facing microphone adjacent to the camera situated within the screen bezel. If the screen protector covers the camera, it will also likely cover the associated microphone. If applicable, remove the screen protector.
Otherwise, you would be best advised to visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad:
Genius Bar Reservation and Apple Support Options - Apple