Please note: the following information does not constitute professional medical advice, and is provided for general informational purposes only. Please speak to your doctor if you have tinnitus. A notch is a segment of audio that is "cut out" of a sample of audio. To understand what this looks like, check out the image below: [caption id="attachment_1372" align="aligncenter" width="155"]What is a Notch? What is a Notch?[/caption] A 4 kHz notch is just a piece of sound energy that has been "notched out" at that specific frequency. To learn more about the notching process, check out our FAQ.