The frequency resolution (bandwidth) of the analysis can be set to either 10Hz
or 20Hz, with the shortest files that can be analyzed being ~320ms- and
~160ms-long respectively.
It is important to note that this length limit does not apply to the time interval
for roughness and spectral profile estimation, which can be as short as 1ms, although such short time intervals may be both impractical
(in terms of the amount of data reported) and meaningless (in terms or roughness
changes).
Rather, the limit applies to the shortest file that can be submitted for analysis
and to the earliest and latest points within a file for which roughness values
and spectra can be calculated.

For example, given frequency resolution of 10Hz, the
earliest (latest) point within a file for which a roughness value can be
calculated will be ~160ms from the beginning (end) of the file, corresponding to
the mid-point of the shortest file that can be analyzed.

More importantly, although 10Hz frequency resolution means that frequency
components less than 10Hz apart will remain unresolved, the frequency values
reported will not necessarily be in multiples of 10 but will have <1Hz precision. For more details, make sure you read the information on the
signal analysis method used.

The default value for this parameter is "10Hz." The value "20Hz" should be
selected only if it is certain that the sound files submitted for analysis
contain no components separated by less than 20Hz in frequency.

For example, 20Hz represent ~ a minor 2nd harmonic interval for fundamental
frequencies around F4 (see a chart of
equal temperament fundamental frequencies).
With the analysis bandwidth set at 20Hz, minor 2nd harmonic intervals below F4
will correspond to fundamental frequencies that will be interpreted as unisons
by the analysis, distorting the roughness calculation results. The lower the
fundamental frequency of the tones making up the sound files analyzed, the more
severe the distortion of the roughness calculation results will be. In fact, for
fundamental frequencies around F2, 20Hz bandwidth represents ~ a major 3rd, and
would wrongly interpret this and all narrower intervals as unisons. The
only benefits of selecting 20Hz over 10Hz resolution are a) the ability to
analyze shorter files and b) faster calculations.