Sound Spectrum Pro for Windows

RTA Display Mode

Shows the energy (RMS) within each frequency band. The band can be chosen from 1 octave to 1/24 octave.
Choose it from the Mode menu.
If well calibrated, it will show correct dB SPL values and the dBA, dBC and dBZ weighted total sound levels will be accurate.
The weighted total sound pressure levels (dBA, dBC and dBZ) are calculated from 20Hz to 20kHz.
For 1 octave bands, the Noise Criterion (NC) and Noise Rating (NR) values are calculated and displayed.
The band energy calculations are based on the results of a FFT.
For 1 octave to 1/6 octave, the bands are aligned with 1kHz and the shown band center frequencies are the standard "preferred" ISO rounded frequencies. For 1/12 and 1/24 octave, the bands are aligned with the standard musical pitch (note A4 = 440Hz).
Select View > Max peak to display the frequency and level of the highest peak.

Is a measure of the effective sound pressure, relative to the reference level of 20 µPa (microPascal).
Is expressed usually in dB SPL = 20 * log(p rms / p ref).

All the settings for FFT apply.
RTA as bar graph - Traditional bar graph RTA, as opposed to line steps (try it!).