PDCON:Conference/Pure Data implementation of an ESS-based impulse response acoustic measurement tool

Pure Data implementation of an ESS-based impulse response acoustic measurement tool

Serafino Di Rosario, Buro Happold Ltd, London (UK) Katja Vetter, Independent PD programmer

Impulse response (IR) measurements for assessing acoustic properties of spaces have been used by acousticians and audio professionals for a long time, with various techniques and test signals. Of these, the Exponential Sine Sweep (ESS) method, successfully advocated by Angelo Farina in the last decade, has outstanding properties.

This paper describes a Pure Data implementation of the ESS method. The need for a Pure Data implementation was due to the lack of features in commercial tools for some particular measurement methods. For example PA system speech intelligibility testing where it is not possible to use the same laptop to generate the test signal and to acquire measurement microphone signal was not an feature available in commercial software. This limitation has caused the author frustration while performing professional IR measurements.

The paper proposes a dedicated Pd class [expochirp~], featuring a modified mathematical formulation of the exponential chirp. Strict conditions control not only the frequencies in the chirp but also the phase at any point. A chirp thus generated exhibits minimum ripple in the high frequencies without compromising the frequency range. For the low frequencies ripple, the optimum was found in a rigorously dimensioned time domain window. Mathematical formulae and comparative results will be presented in the upcoming article.

All the other requirements to build the conceived tool are met by existing Pd object classes, notably the important partitioned convolution class [partconv~] written by Benjamin Saylor.

With the refined test signal as a starting point, a series of Pd patches for IR measurement is being built, with user-friendly interface, and graphical representation of data in all stages of the process. A basic toolkit is now finished, comprising chirp generator, impulse response recorder, sample-precise editor, and a spectral data analyser. The modular setup of the project allows for additional tools to be developed one by one. Future developments will focus on room acoustics parameter derivation according to ISO 3382:2009 (part 1 and 2), and on analysis and processing of Ambisonics measurements. The authors express the hope that ExpoChirpToolbox will be useful by virtue of its quality and openness, not only for professional audio engineering, but also for educational purposes.