This SoundCheck test sequence measures headphone active noise cancellation (ANC). It measures both the active and passive noise cancellation and calculates total attenuation over the operating frequency range of the headphones. Passive Attenuation is the amount of noise that is reduced at the ear simply by the headphones being worn. Active Attenuation is the amount of noise that is further reduced by turning on the device’s active cancellation circuits. Lastly, Total Attenuation is the combined reduction in noise from passive and active sources and is what the end user of the product will experience.
To calculate these metrics this SoundCheck test sequence performs three separate measurements using a Head and Torso Simulator and a small speaker which serves as a noise source. This is a simple, low-cost alternative to using a diffuse background noise environment with multiple speakers playing uncorrelated noise, although the sequence could be user-modified to support this.