ExpoChirpToolbox: a Pure Data implementation of ESS impulse response measurement
Author: Katja Vetter, Independent Pd programmer and Serafino Di Rosario, Buro Happold Ltd, London (UK)
Download full paper: Media:ExpoChirpToolbox- a Pd implementation of ESS impulse response measurement.pdf
Impulse response (IR) measurements for assessing acoustic properties of spaces have been used by acousticians and audio professionals for a long time, with the help of different 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 practical measurement issues (i.e. PA system speech intelligibility testing in large spaces). This limitation has caused the authors' frustration while performing professional IR measurements.
The paper proposes a dedicated Pd class [expochirp~], featuring a modified mathematical formulation of the exponential swept-sine signal. Strict boundary conditions have been applied to 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~].
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 multi-channels 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.
A web page have been started showing screnshots of the patch and improvements in the test signal generation .
- A. Farina, "Simultaneous Measurement of Impulse Response and Distortion with a Swept-Sine Technique", pre-print of the 108th AES Convention, Paris (France), 19-22 February 2000
- [partconv~] written by Benjamin Saylor
4th international Pure Data Convention 2011 Weimar ~ Berlin