Cocktail party effect

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Despite the noise at the party, the other person's words can usually be understood

The cocktail party effect , also known as intelligent or selective hearing , describes the ability of the human sense of hearing to extract the sound components of a certain sound source from the mixture of interfering sound when several sound sources are present. For example, at a cocktail party where many people are speaking at the same time, the hearing is able to hear especially the words of a single speaker and suppress those of the others.

description

The hearing achieves a noise suppression of 9 to 15  dB , that is, the sound source on which a person is concentrating is perceived two to three times louder than the (disturbing) ambient noise. This means that in a noisy environment a person is able to seek out the sound of a single sound source simply by hearing. A microphone set up in such an environment , on the other hand, appears to mainly reproduce the background noise. Furthermore, the cocktail party effect means that sound sources are perceived in rooms with little spatial impression: the signals sound “dry” and hardly fade away. A microphone set up in such an environment, on the other hand, reproduces signals with a strong spatial sound.

In addition, the hearing can concentrate on any sound sources without moving the head and achieves similarly good results for lateral sound sources.

The signal processing strategies of the human ear have not yet been fully deciphered. All technical attempts to extract the signals of a source from a sound mixture with only two sound sensors achieve significantly poorer results. In sound recording technology, direction-specific recordings still rely on microphone arrangements or microphone arrays with a larger number of microphones and directional microphones (see also localization ).

Influences

The cocktail party effect is a binaural effect, it only occurs when hearing with both ears. People who only have one functional ear or who rely on a hearing aid are therefore much more affected by background noise than people who hear equally with both ears.

The cocktail party effect is closely related to the ability to localization of sound sources connected. Once the hearing has determined the direction of a sound source, it is also able to distinguish the sound components in this direction from parts from other directions.

It is assumed that the hearing performs a kind of cross-correlation between the sound components of both ears. Cross-correlation functions map signal components onto an axis that describes the time shift between the two signals. If a sound comes from the side with an interaural time difference (English Interaural Time Difference, ITD) of z. B. ITD = 0.3 ms, this signal is found again at the 0.3 ms point of the correlation axis. The presence of several sound sources results in complex correlation patterns in which statistical parameters such as mean value and variance depend on the directions and signal components of the sound sources involved. The hearing is obviously able to evaluate these patterns and use them to determine the signal component from a desired direction. In addition to correlation methods for interaural transit time differences, there are also those for interaural level differences (Interaural Level Difference, ILD).

In addition to the direction-specific signal processing, the hearing also uses other effects for noise suppression, such as knowledge of the signal properties; z. For example, non-verbal sounds and noises in speech can be ignored as irrelevant, such as the expectation of certain sounds with certain mouth movements.

history

The term was also used in conversation analysis when researchers began recording conversations and discovering the inadequacy of monophonic microphones.

See also

literature

  • Cherry, E. Colin: Some experiments on the recognition of speech, with one and with two ears . In: Journal of the Acoustical Society of America . tape 25 , 1953, ISSN  0001-4966 , pp. 975-979 , doi : 10.1121 / 1.1907229 .
  • Slatky, Harald: Algorithms for the direction-selective processing of sound signals: the realization of a binaural cocktail party processor system . 1992 ( online - dissertation, Ruhr University Bochum).

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