2

Frequency resolution

Octave bands

Frequency resolution

The sounds we hear are rarely pure tones at a single frequency but rather a mixture of frequencies of varying amplitudes. Some sounds, such as a whistle or a horn, have frequencies concentrated in relatively narrow regions of the audio spectrum, which ranges from approximately 20 Hz to 20,000 Hz. Other sounds, more generally thought of as noise, include components from many regions of the entire spectrum.

When analyzing sound as noise, we usually are concerned with the total impact of the sound signal. In other words, we are usually satisfied with a broadband measurement of sound in the environment. When we are seeking to isolate a sound from other sounds, for instance to detect the source of a sound or to measure how much particular sounds contribute to the overall sound level, we may want to look at the frequency components of the sound.

Octave bands

The ability of an instrument to separate a signal into its frequency components is known as a spectral analysis. In sound pressure measurement, the audio spectrum is divided into adjacent frequency bands called octaves, where the center frequency of each octave band is twice the center frequency of the octave band directly below it. There are eleven octave bands in the audio spectrum.

Figure 1-2 illustrates the relationship between the bandwidth of a typical sound measuring instrument and the octave bands that span the audio spec- trum. Note that the highest and lowest octaves at 16 Hz and 16 kHz lie entirely within the bandwidth of the instrument.

Level

Figure 1-2: Octave bands

Models SE and DL

Page 15
Image 15
3M DL, SE user manual Frequency resolution, Octave bands, Level