Jan-Gerrit Richter

On the influence of continuous subject rotation during HRTF measurements

In recent years, the measurement time of individual Head-Related Transfer Function (HRTF) measurements has been reduced by the use of loudspeaker arrays. The time reduction is achieved by some kind of parallelization of measurement signals. One such fast system was developed at the Institute of Technical Acoustics, RWTH Aachen University and is evaluated in this paper. When measuring HRTFs, the subject is usually rotated by some angle, and stops and waits for the measurement signal to complete before moving to the next measurement angle. It was shown that with this static approach a comparable results to a traditional measurement using a single speaker could be achieved. To further reduce the measurement time, a slow continuous subject rotation can be used instead. While this rotation will violate LTI (linear, time-invariant) requirements of the commonly used signal processing, the influence is assumed to be negligible. As the subject is rotating during the measurement sweep, different azimuth angles are measured per frequency. This frequency dependent offset in the measurement positions has to be corrected during the post processing. To this end, a spherical harmonic decomposition and reconstruction is applied as an interpolation method. To quantify the influence of the rotation and the subsequent post processing, a subjective and objective comparison between statically and continuously measured objects is shown in this paper.In recent years, the measurement time of individual Head-Related Transfer Function (HRTF) measurements has been reduced by the use of loudspeaker arrays. The time reduction is achieved by some kind of parallelization of measurement signals. One such fast system was developed at the Institute of Technical Acoustics, RWTH Aachen University and is evaluated in this paper. When measuring HRTFs, the subject is usually rotated by some angle, and stops and waits for the measurement signal to complete before moving to the next measurement angle. It was shown that with this static approach a comparable results to a traditional measurement using a single speaker could be achieved. To further reduce the measurement time, a slow continuous subject rotation can be used instead. While this rotation will violate LTI (linear, time-invariant) requirements of the commonly used signal processing, the influence is assumed to be negligible. As the subject is rotating during the measurement sweep, different azimuth angles are ...

Spherical harmonics based HRTF datasets: Implementation and evaluation for real-time auralization

HRTF filters used in most binaural synthesis application stem from a discrete set of either measured or simulated far-field data. While this data format allows fast filter generation times and is fairly straightforward to use, correct filter representation is only possible for the measured points while an interpolation is needed between the points. As these interpolated filters are not a physically correct representation of the HRTF, this approach is not suited for the auralization of very small head movements that humans tend to do to improve localization [1]. For the auralization of sources in the vicinity of the listener the near-field HRTF is important [2]. With discrete HRTF data sets, multiple measurements for different distances have to be combined to account for this.

Acoustic directivity measurement using the ITA-Toolbox

[1] Berzborn, Marco, et al. „The ITA-Toolbox: An Open Source MATLAB Toolbox for Acoustic Measurements and Signal Processing.“ 43rd Annual German Congress on Acoustics DAGA (2017). [2] Dietrich, Pascal, et al. „On the optimization of the multiple exponential sweep method.“ Journal of the Audio Engineering Society 61.3 (2013): pp. 113-124. [3] Noisternig, Markus, et al. „High-Resolution MIMO DRIR Measurements in an Opera Hall.“ 42nd Annual German Congress on Acoustics DAGA (2016). [4] Richter, Jan-Gerrit, et al. „Evaluation of a Fast HRTF Measurement System.“ Audio Engineering Society Convention 140. Audio Engineering Society (2016). [5] Shabtai, Noam R., et al. „Generation of a reference radiation pattern of string instruments using automatic excitation and acoustic centering.“ The Journal of the Acoustical Society of America 138.5 (2015): EL480-EL486. References Signal processing At its core, the ITA-Toolbox [1] provides functions to read, manipulate, and save objects. For the determination of the directivity, the following steps are required: • detection of the first arriving sound, • time shift of the impulse response, • time windowing for artifact removal, • regularized division to improve signal-to-noise ratio.

Fast measurement of the temperature distribution in a blast furnace using impulse response measurement

The temperature profile on top of a blast furnace gives meaningful information about the heat distribution and the activity of the ballast below. Since a direct measurement using temperature probes is both complicated due to the filling procedures and expensive due to the repeated damage of the sensors. An indirect measurement of the temperature is given by the measurement of the propagation delay for sound which by a known distance reveals the average temperature of the gas in between source and receiver position. The temperature distribution is then derived by a tomographic approach in one plain above the blast furnace with different source and receiver positions. Basically, this method is not new and it is used with stochastic (pneumatic excitation) signals in many applications. The typical measurement time for a single temperature profile takes about 20-30 seconds. It is obvious that the temperature distribution will not be stable for such a long time; hence, the measurement results are not very much ...