1. Choosing the right microphone
The microphone in many laptops is located right next to the cooling fan. This is a major design flaw. Connect a USB microphone such as the Blue Yeti or Samson Q2U. The built in microphone in a MacBook is reasonable.
4. Find a solid internet connection
Wifi is far less reliable than wired connections. 3G, 4G, LTE even less so. Find a fixed internet connection and connect an ethernet cable from the modem / router to the computer.
5. Check the computer's audio settings
Check that the input volume slider in your computer's audio input settings isn't too low or too high. Uncheck the box marked 'Use Ambient Noise Reduction' in Mac OS. Windows has a similar setting.
Following these five tips will lead to a far higher standard of interview over ipDTL. It will also make Skype or Facetime calls more bearable. Oh, and remember to use headphones.