## FAQ-a013

FAQ-A013：What is "Octave Band Noise"?

[Answer] "Octave Band Noise" is a noise signal that extracts only energy of a bandwidth of a certain one octave frequency with respect to white noise and pink noise.

The noise signal can be used for various purposes as a reference sound source for environmental sound measurement, sound tuning, auditory effects like tinnitus relief and sound masking.

Our app "Octave-band Colored Noise" provides an octave band noise can be output programmably.

We will explain "Octave Band Noise" in more detail. An octave is a pitch that doubles the ratio of frequencies to a certain frequency. And the octave band is the bandwidth of the frequency where the ratio of the upper and lower frequencies centered on a certain frequency is exactly one octave.

The center frequency of this octave band is called the center frequency, and the frequency band for the center frequency fo ranges from the lower limit frequency fo/√ 2 to the upper limit frequency fo*√2. For example, the center frequency of an octave band is 1 kHz, 2 kHz, 4 kHz ,,,, and one octave is divided into three in the 1/3 octave band.

"Octave Band Noise" is a noise signal that extracts only a specific frequency band with the band-pass filter with the octave band characteristics. Using the noise, it is possible to evaluate only the target frequency band. By measuring the pink noise of a specific frequency band with a real-time analyzer, it is possible to make sound adjustments and measure noise source characteristics that are not affected by other frequency bands.

The figure below shows an example of generating 1/1 octave band noise at the center frequency (1000 Hz and 4000 Hz) with white noise as the source signal. It is FFT analysis result by our audio analyzer app "Audio Frequency Analyzer". Since this measurement result is an instant observation value, it can obtain a flat frequency characteristic within the octave band in time averaging.

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