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Combination Tones in the Model of Central Auditory Processing for Pitch Perception

Ziębakowski T.

Archives of Acoustics

2012

Vol. 37, No. 4

571-582

This work addresses the problem of difficulties in classical interpretation of combination tones as non- linear distortions. One of the basic problems of such an interpretation is to point out the sources of these distortions. Besides, these kinds of distortions have numerous “anomalies” which are difficult to explain on the grounds of physics or physiology. The aim of the model presented in this paper is to show that combination tones phenomenon can be explained as an effect of central mechanisms. Most of existing theories of pitch perception focus mainly on virtual pitch perception and do not take into account com- bination tones as an element of the same mechanism. The proposed model of central auditory processing for pitch perception allows one to interpret in a coherent way both virtual pitches and combination tones phenomena. This model is of a demonstrative nature and gives an introduction to more advanced model. It belongs to the class of spectral models and it will be shown that such a model can be in a simple way extended to spectral – time model which is partially consistent with autocorrelation models.

Combination Tones in Violins

Lohri A., Carral S., Chatziioannou V.

Archives of Acoustics

2011

Vol. 36, No. 4

727-740

In this study we investigate the appearance of combination tones in violins. Most authors in recent times have emphasised that combination tones occur inside the ear exclusively (intra-aural). This assumption will be subjected to scrutiny based on evidence found in an empirical study in which combination tones were measured outside the ear (extra-aural). Measurements were performed in which a violinist played two tones of a particular musical interval simultaneously. This was recorded and subsequently analysed using a Fourier Transformation. In addition to the partial tones of the primary interval, the resulting spectrum showed frequencies corresponding to combination tones. Similar measurements on the viola and violoncello also revealed the existence of extra-aural combination tones. Such frequencies may influence the timbre of simultaneous intervals played on string instruments. In another experiment the violin was excited using an electrodynamic mini-shaker with the aim of localising the origin of extra-aural combination tones. A newly devised tone matrix was used as a theoretical approach which computes all potential combination tones that may occur between any pair of partial tones. The detailed analysis of musical intervals by both the frequency spectrum and the tone matrix shows characteristic mirror and point symmetries in the partial tone structure. The discussion focuses mainly on the audibility of extra-aural combination tones and on ‘the combination tone 1’. This research opens up new perspectives and questions relevant for interpreters, composers, violin makers and violin acousticians.