Psychoacoustics

Psychoacoustics is a branch of psychophysics. It deals with the description of the relationship of the human perception of sound as an auditory event and with its physical sound field quantities as sound event. Processing physical signals to a hearing impression is modeled in multiple stages. These are assigned to the individual ear and cognitive signal processing. So Psychoacoustics examines the relationship of objectively - physical stimulus - the sound waves - and the impression of the recipient - such as loudness, sharpness, tonality, roughness, tonality, impulsiveness, fluctuation strength, etc. It examines laws in this ratio to so create hypotheses about the processing of auditory stimuli and to examine experimentally. There are means of individual or individually different " if-then relationships " are worked out between stimulus and psychological experience. Important applications of psychoacoustics are the sound effects research, telecommunications, audio data compression and sound design.

Parameter

It proves useful to represent purely physical parameters such as level, frequency, bandwidth, duration or degree of modulation on faithful to hearing parameters. As a rule, act in each case several physical quantities on psychoacoustic size. This should be evaluated as a single sensation independently of other sensations. The scale psychoacoustic quantities describe the strength of feeling.

The most common psychoacoustic parameters are the parameters Zwicker loudness ( sone unit ), sharpness ( unit acum ), tonality ( unit mel ), roughness ( unit asper ) and fluctuation strength ( unit vacil ). In addition, are tonal and impulsive significant quantities; they are also used in the formation of rating levels. The phon is the unit of psychoacoustic variable volume level.

Methods

Psychoacoustic tests collect subjective judgments of subjects. Since these people judge individually, the results of the tests are valid only on the basis of a statistical analysis of a number of judgments. The methods for collecting the judgments are divided into classical and adaptive methods, where the distinction lies in the fact that the course of an adaptive test is affected by the judgments of the subject, while the classical methods remain unaffected.

Classical methods are: constant -stimulus method, size estimation, Einregelungsmethode and complete paired comparison.

Adaptive methods are: Forced -choice methods (2- AFC, 3 - AFC, 4 - AFC) and Békésy tracking.

" Equal loudness curves " or more accurately " curves of equal loudness level" ( Isophone ) were first created in 1936 by Fletcher- Munson. Next, measurements were made by Robinson - Dadson known that have been added to the international ISO Recommendation R 226 1956. Since 2003 there is new corrected curves as "Normal equal- loudness -level contours - ISO 226:2003 Acoustics International Organization for Standardization (ISO), 2nd edition ".

Modeling

Psychoacoustic tests revealed that the human ear is essentially with a number (eg 24 bands according to the Bark scale) of bandpass filters can be modeled. This structure is similar to the analysis portion of a vocoder.

• A key concept here is the critical bandwidth. If two sounds in a band, it is just a sound can be heard, possibly with an amplitude modulation or roughness. Only when the frequency spacing of the tones is greater than the critical bandwidth, they fall into two separate filter channels and therefore also found to be of two tones. The critical range varies over the listening area, is not constant.
• The transshipment of rhythm in tone sensation when increasing the frequency of a pulse generator can also be explained by the mentioned model.
• The sense of tonality ( Mel ) is true only about the same as the physically measurable frequency.
• The perception of loudness is true only approximately match the logarithm of the physically measurable sound pressure.

Subtle tones are masked by louder obvious, so are not noticeable, although physically very well detectable. A first sounding loud event can cover a then next event. A erklingendes for a silent event Louder can also obscure the former. This allows to draw conclusions on the coupling of the channel data.

• The transfer of physical measurements on the perception is possible only with the greatest care and caution. Thus, for example, simple sound level meters not able to reproduce the noise pollution. There are documented cases where Lärmdämmmaßnahmen were evaluated by all subjects as positive, however, were classified by the simple instrumentation in a deterioration. These discrepancies always occur when the meter takes no account of the above operation of the hearing.

Scientist

Significant work was done by:

• Amar Gopal Bose (born 2 November 1929), founder of Bose Corporation
• Hermann von Helmholtz (1821-1894)
• Carl Stumpf ( 1848-1936 ): tonal psychology, 2 vols 1883-1890 (main station)
• H. Fletcher and W. A. Munson ( b. 1933 )
• Robinson and Dadson ( b. 1956 )
• J. F. Schouten: The perception of pitch. Philips Technical Review 5 (1940 ) 286-294.
• Eberhard Zwicker (January 15, 1924 - November 22, 1990 )
• Stanley Smith Stevens ( 1906-1973 )
• Jens Blauert (* 1938): Spatial hearing. S. Hirzel Verlag, Stuttgart 1974, ISBN 3-7776-0250-7.
• Georg von Békésy (1899-1972): Experiments in hearing, 1960 ( traveling wave theory )
• Martin Ketel ( * 1943 ): The psychoacoustics of human beings. 1964

Various known acoustic illusions - comparable to the better-known optical illusions - illustrate the complexity of the hearing.