Filter Banks

Octave filter resolution is limited because only 11 octaves exist in the 16 Hz–16 KHz range. To overcome the limited resolution of octave filters, you can use other filters known as fractional-octave filters.

Rather than covering one octave with a single filter, N filters are applied per octave in order to improve resolution. Of the fractional-octave filters, the third-octave (1/3) filter is used widely for fractional-octave analysis. The following figure shows the 1/3 octave response at frequencies of 500 Hz, 630 Hz, and 800 Hz.

Figure 32. Third-Octave Filter Response

1378

Fractional-octave analysis is a CPU-intensive operation. Increasing the number of filters applied to a signal increases the demands placed on the CPU and can result in increased computation time.