ESDU 08018:2011

There is a standard file structure for recording noise spectra
and other data which is used throughout the ESDU Aircraft Noise
Series. Most Items employ this Common Data standard. There is an
on-going programme to enable every relevant program to read and
write such data files.

This standard file specification enables computer programs from
the ESDU Aircraft Noise Series to be run successively, that is, the
output from one program can be used as an input for another.

At other times, the user may wish to combine spectral levels
contained in Common Data Files that have been generated by
different programs. This Item facilitates the combination of
spectral levels.

Spectra at any given location can be added or subtracted either
on a logarithmic or an arithmetic basis. Aircraft or engine noise
is usually predicted by calculating the noise produced from more
than one source and then adding the individual source noise
predictions together. The addition of such spectra must be
performed on an energy, i.e. logarithmic, basis. If, however,
corrections like those for ground-reflection, atmospheric
absorbtion attenuation or duct liner attenuation have to be made,
arithmetical combinination of spectral levels is required.

A computer program known as ESDUpac A0818 accompanies this
Item.

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