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Imitating the Influences of Nonlinear Devices on Audio Signals by Conventional Equalisation

Nachahmung der nichtlinearen Einflüsse auf Audiosignale durch Equalizing
: Karapetyan, A.; Fleischmann, F.; Plogsties, J.

Verband Deutscher Tonmeister -VDT-:
Expertise in audio media. 28. Tonmeistertagung, TMT 2014. CD-ROM : 20.11. - 23.11.2014, Cologne
Bergisch-Gladbach: Verlag VDT, 2014
ISBN: 978-3-9812830-5-1
Paper RD-9
Tonmeistertagung (TMT) <28, 2014, Cologne>
Fraunhofer IIS ()

It is difficult for small electro-acoustic loudspeakers to produce sounds below their cut-off frequencies. Simply amplifying the low-frequency range leads to undesirable non-linear effects such as distortion and clipping. A more sophisticated approach promises to evoke the illusion of a more extensive low-frequency response of a loudspeaker while not physically radiating more power at those frequencies. This apparently can be achieved by making use of
the ‘missing fundamental’ effect. A nonlinear device (NLD) generates harmonics which should psychoacoustically intensify the audibility of the corresponding fundamental frequency. The same technique may also be used to enhance high frequencies, commonly referred to as using an ‘exciter’. Different sound items were processed with several types of NLDs. The result is strongly dominated by the amplified harmonics. Furthermore, it is difficult to assess whether the fundamental frequency gets perceptually enhanced due to the absence of an objective measurement criterion. This investigation deals with the question of whether the perceptual differences caused by the NLDs are mainly noticeable due to the redistribution of energy and thereby can also be achieved by conventional filtering such as equalisation. In this novel approach, the difference in magnitude response before and after processing an item with a
NLD is determined. This transfer function is then applied to the same item without the use of a NLD. The results of a listening test with 15 listeners showed that the differences between non-linear processing and equalising were hardly audible. For one out of three sound items the difference was significant.