Octave Bands. The overall noise from a piece of equipment can be subdivided into the noise in various frequency regions to give more detailed information on the character of the noise; for example, whether it is a low-pitch roar or high-pitch squeal. The most common subdivision of frequency is into octave bands, which are contiguous frequency bands whose centre frequencies double for one to another. These centre frequencies have been fixed by international agreement and, for engineering purposes, they range from 31 Hz to 16 kHz. The 31 Hz, 8 kHz and 16 kHz bands may not always be required. Sound-level meters can be equipped with band-pass filters so that they measure the total sound energy within an octave band of frequencies. This information may be required by a purchaser who is concerned with reverberation in confined spaces or noise propagation over large distances, because both these effects vary with frequency. They may also require it for the design of noise-control measures.