SIDEBANDS-FACTS AND ARTEFACTS

• Published in: Bioacoustics (Berkhamsted) Vol. 10; no. 2-3; pp. 219 - 224
• Main Author: FROMMOLT, KARL-HEINZ
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 01.01.1999
• Subjects: acoustic analysis; Animalia; Brackish; Freshwater; Marine; non-linear phenomena; sidebands
• ISSN: 0952-4622; 2165-0586
• DOI: 10.1080/09524622.1999.9753432

Recently more and more examples of non-linear phenomena in animal vocalisations have been described. One such phenomenon is the occurrence of sidebands, which have been discussed in this journal as possible artefacts of digital analysis (Vielliard 1993, Jackson 1996). Sidebands occur when a carrier frequency is amplitude or frequency modulated. In a spectrogram sidebands appear as additional frequency bands above and below the carrier frequency whereby the difference between upper sideband and carrier frequency is equal to the difference between carrier frequency and lower sideband. Now there should be no doubt that sidebands in animal vocalisations really occur. Examples of sidebands have been shown for amphibians (Gerhardt 1998), birds (e.g. Greenewalt 1968), and mammals (Wilden et al. 1998). However, researchers in the field of bioacoustics should be very careful when interpreting spectrograms to consider the origins of these effects. Sidebands can be produced by the sound generating organs of animals but also have their origin in the electronics of the recording device. Here I will show examples of both sidebands produced by animals and sidebands that are artefacts. All spectrograms were calculated using AvisoftSASLab software.