Anton Noll

  • Objective:

    Acoustic holography is a mathematical tool for the localization of sources in a coherent sound field.

    Method:

    Using the information of the sound pressure in one plane, the whole three-dimensional sound field is reconstructed. The sound field must be coherent and the half-space in which the sources are situated must be known.

    Application:

    Acoustic holography is used to calculate the sound field in planes parallel to the measured plane. Normally, a plane near the hull of the structure is chosen. Concentrations in the plane are assumed to be the noise source.

  • Objective:

    In certain measurement setups, such as the measurement of gear mechanism behavior undergoing load reversal, the fine structure of the rotation speed function within a single rotation is interesting. In these situations, measurement errors caused by irregular cog intervals or by other failures of cogwheels are disturbing and must be corrected.

    Method:

    From a reference signal, the distribution parameter of the rotation angle for each cog of the cogwheel is assigned as a cogwheel model. This cogwheel model can minimize the measurement failures caused by the cogwheel if its cog is implemented in synch with the measurement signal. If the reference signal and the measurement signal come from different measurements, the synchronicity has to be established first. The calculation of the shift between the two signals is determined by the cog index, which has the maximum correlation of the rotation angle allocation between the reference signal and the measurement signal.

    Application:

    The developed method will be used as a module in the acoustic measurement and analysis system PAK.

  • Objective:

    This project aims to develop an independent modulus for the wavelet analysis that contains a simple program interface and can be used flexibly.

    Method:

    The implementation was in C++ in the form of a wavelet analysis class and a signal queue. Features:

    • The Input/Output data format can be chosen at run time. The Input and the Output are separately configurable.
    • There are several possibilities for choosing the array and distribution of the frequency bin. The frequency bin vector can also be transferred.
    • Seven wavelets are implemented.
    • A down-sampling method can be used for the acceleration (factor: 1.2 convert frequency bins are chosen automatically).
    • Because of the disjunction in signal queue and analysis, an asynchrony Input/Output is possible.
    • Compiling an optimized numerical library can be achieved. Currently, the application of the "Intel® Signal Processing Library" (SPL) or of the "Intel® Integrated Performance Primitives" (IPP) is possible.
    • The signal queue class can be used independently of the analysis class. It also implements the down-sampling function.

    Application:

    The developed classes are used as a modulus in the acoustic measurement and analysis system PAK. The analysis class was also integrated as a signal processing atom WLLIB in STx.

  • Objective:

    The usual transformation in acoustics is the Fourier-Transformation. A fast and simple implementation is the windowed Fast Fourier Transformation. A disadvantage of the FFT is that all frequencies are equally spaced in the time frequency plane. A logarithmic spacing that allows keeps the relative resolution in the frequency plane constant is the Wavelet Transformation. This gives the possibility of a higher temporal resolution in the high frequency plane. Several types are implemented in STX and PAK.

    Method:

    A higher temporal resolution is possible, if quadratic transformations defined in the Cohen Class are used. The Windowed Pseudo Wigner Ville Distribution and a discrete version of the Choi-Williams Distribution are implemented in STX and PAK. Disadvantages of these transformations are the cross products that are reduced by smoothing in the different transformations of the Cohen class.

    Application:

    A handbook is written for or the practical use of the difficult transformations. The Handbook documents the possibilities and the limits of the transformations