We’ve already covered how noise cancelling , and in a nutshell, noise cancellation is based on the principle of phase cancellation. Sound waves that are 180 degrees out of phase, or the inverse of one another, cancel out when summed together. Think of it as adding -1 to +1, and you end up with zero. The idea with noise cancellation is to record the background noise, invert the noise signal to create “anti-noise,” and then add it to your output signal, which includes your music. The anti-noise signal cancels out the actual background noise at the point it reaches your ear. The idea is surprisingly simple and dates back to the 1930s, but it’s easier said than done.

The biggest issue with ANC is sampling ambient sounds accurately enough to provide the maximum degree of attenuation. Microphones must capture the noise, and the phase of the cancellation waveform leaving the headphone drivers needs to perfectly line up with the phase of the noise when it reaches your ear. These systems need to be finely tuned, but even then you won’t ever see 100% cancellation. Instead, between 20-40dB of noise reduction is quite common, which cuts the background noise level you hear to between one-quarter to one-sixteenth its original level. A considerable amount.