If you want good quality audio in an interview recorded on an iPhone or need to add a voiceover for the video you're editing on your iPad, it's best to connect an external microphone. Here's how to do it.
You can't just plug a standard microphone into the 3.5mm jack or into a Lightning-to-USB adaptor. There are plug-and-play Apple-certified models, but those cost upwards of $150. Instead, you can use any microphone. Amit Agarwal of Digital Inspiration says the key item is a powered USB 3.0 hub.
Make sure your hub is powered on. Using a Lightning-to-USB adaptor and a standard USB cable, connect your iPhone or iPad to the hub. Connect your microphone to the hub in another port. Open up any app like iMovie or GarageBand and start recording your voice. You might see an error message like "Cannot use device — The connected device requires too much power". But don't worry, just dismiss the message and carry on.
How to Connect an External Microphone to your iOS Device [Digital Inspiration]