Theory

The slider offers the nominal centres:

octave: 16, 31.5, 63, 125, 250, 500, 1000, 2000, 4000, 8000, 16000 Hz;
1/3 octave: from 10 Hz to 20 kHz (10, 12.5, 16, 20, 25, 31.5, 40, 50, 63, 80, 100, ...).

A typed value, or one from an older file, snaps to the nearest centre on a logarithmic scale. Each selected band contributes three solved frequencies, equation (1), and the lowest and highest frequencies of the sweep become the lower edge of the first band and the upper edge of the last, equation (2). The band value is the Simpson average of its three points (Frequency spacing).

Equations

\{f_L, f_C, f_U\} = \{f_C 2^{-b},\ f_C,\ f_C 2^{b}\}, \qquad b = \tfrac{1}{2}\ \text{(octave)},\ \tfrac{1}{6}\ \text{(1/3 octave)}

(1)

f_{min} = f_{C,first}\,2^{-b}, \qquad f_{max} = f_{C,last}\,2^{b}

(2)

where	meaning	unit
$f_C$	Nominal centre frequency	Hz
$f_L, f_U$	Lower and upper edge	Hz
$b$	Half band width in octaves	-
$f_{C,first}, f_{C,last}$	Centres of the first and last selected band	Hz

Default and rule

Default: the bands nearest the current frequency range
Rule: When octave or 1/3-octave spacing is selected, the slider starts on the saved bands, otherwise on the bands nearest the current $f_{min}$ and $f_{max}$ .
Source: The band construction is the program's own: each band is solved at its lower edge, centre and upper edge (base-2 edges), and the band edges define the frequency range of the sweep. The nominal centres are the ISO 266 preferred frequencies.

Valid range octave: 16 Hz to 16 kHz; 1/3 octave: 10 Hz to 20 kHz (nominal centres)

Values

Any first and last centre of the list; the last must not be below the first (they are swapped otherwise).

Theory

Equations

Default and rule

Valid range octave: 16 Hz to 16 kHz; 1/3 octave: 10 Hz to 20 kHz (nominal centres)

Related 3