MP3 Stimuli in room Acousitics

In some situations it is very inconvenient or even impossible to perform an impulse response measurement where both the excitation source and the receiving microphone have to be wired to the same measurement system. Think for instance of speech intelligibility measurements through public address systems in railway stations or large airport halls. This is usually solved by open loop measurements playing prerecorded stimulus wave files from a CD player or laptop PC. Given the growing popularity of the MP3 format, which is roughly 10 times smaller in size than the uncompressed PCM format, the question has arisen whether it is also possible to use MP3 stimulus files. To investigate this, PCM and MP3 stimulus based measurements were performed with DIRAC, a room acoustics measurement software tool that supports open loop measurements. It is shown that the investigated room acoustical parameters are not significantly affected by MP3 compression of sweep and MLS stimuli. Using an open loop measurement system, such as DIRAC, it is therefore possible to perform room acoustical measurements using MP3 stimuli, played from any portable device (e.g. iPod, mobile phone, etc.).