Narrow-Band Noise. When the noise from a source contains a pure tone or narrow-band component which is noticeable to the ear as a noise of distinguishable pitch, and which represents a dominant feature of the total source noise, then the source noise should be regarded as containing narrow-band noise for the purpose of this Specification. Note: Where there is doubt about the subjective assessment of narrow-band noise it should be resolved by narrowband analysis, using an instrument with a band width not more than 10 Hz or 1%, whichever is the less.