DEVELOPMENT OF BUILDING ACOUSTICS SIGNAL PROCESSING SOFTWARE TO MINIMISE THE USE OF “BLACK BOX” HARDWARE AND SOFTWARE

Most acoustic signal processing is now performed digitally in commercial “black box” hardware and/or software running on a personal computer. CSIRO has encountered intermittent problems with “black box” acoustic signal processing software when measuring reverberation time due to the software sometimes deciding that the decay had started before it had. CSIRO eventually discovered that this was partially due to the firmware generating the same random noise signal each time that random noise generation commenced. CSIRO was able to persuade the commercial hardware developer to modify the firmware. The problem was also caused by the intermittent generation of undefined level values. When these undefined level values were averaged with other normal level values for the same relative time in other repeated decays, the average value increased above what it should have been before returning to the expected value when the undefined values ceased to occur. Because the commercial developer of the software was unable to duplicate these intermittent problems and CSIRO does not have the source code of the software, these problems have remained unfixed. A highly respected international standards laboratory has produced measurements in an international sound absorption coefficient round robin which were clearly incorrect. The laboratory believes that this was due to their use of new “black box” hardware and software. These examples show the need to minimise the use of “black box” hardware and software. The release of an open Application Programming Interface (API) for their acoustic signal frontend hardware by a major commercial manufacturer in 2020 has enabled CSIRO to develop their own acoustic signal processing software. This software can perform fast Fourier transforms and fractional octave band filtering up to 24th octave in six channels with a bandwidth of 51.2 kHz in real time. It can also measure reverberation time.