Neighbour tones can be described as a tone that is not heard in the primary frequency you are trying to amplify. For example, if you have a low-frequency sine wave and want to hear it louder than your higher frequencies, then create an extra high-frequency sine wave by adding a small amount of noise at one side of the spectrum (the neighbor or adjacent) and subtracting some from the other side. This creates what is called constructive interference which produces audible results for multiple wavelengths within this range!