Please check to make sure that your mic is enabled.

Here is how to update your privacy settings so that you can start using your microphone again.

1. Click on the main settings tab.  I am talking about Apple's settings tab.  
You will find this button on the home / main page of your device unless you have moved it.

2. Click on Privacy (it's the button above the iCloud button)

3. Click on Microphone

4. Review the apps that are listed and make sure that the setting is set to ON so that the app is allowed to access your photos.  

Most likely, it is currently set to OFF, which is why you are unable to hear your recordings.