Sharpness and Sensory Pleasantness
Previously, there has been a tendency to transfer everything in steady-state sounds not related to the sensations of loudness or pitch, to a residual basket of sensations called timbre. Using this definition of timbre, it is necessary to extract from the
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Previously, there has been a tendency to transfer everything in steady-state sounds not related to the sensations of loudness or pitch, to a residual basket of sensations called timbre. Using this definition of timbre, it is necessary to extract from the mixture of sensations those that may be important. The sensation of "sharpness", which may be related to what is called "density", seems to be one of these. Closely related to sharpness, however inversely, is a sensation called sensory pleasantness. This sensation, however, also depends on other sensations such as roughness, loudness, and tonalness.
9.1 Dependencies of Sharpness Sharpness is a sensation which we can consider separately, and it is possible, for example, to compare the sharpness of one sound with the sharpness of another. Sharpness can also be doubled or halved if variables are available that really change sharpness. The variability of sharpness judgements is comparable to that of loudness judgements. One of the important variables influencing the sensation of sharpness is the spectral envelope of the sound. Many comparisons have indicated that the spectral fine structure is relatively unimportant in sharpness. A noise producing a continuous spectrum, for example, has the same sharpness as a sound composed of many lines if the spectral envelopes measured in critical-band levels are the same. Sharpness increases for a level increment from 30 to 90 dB by a factor of two. This means that the dependence on level can be ignored as a first approximation, especially if the level differences are not very large. Another small effect is the dependence on bandwidth, as long as the bandwidth is smaller than a critical band. No difference in sharpness can be detected whether one tone or five tones fall within one critical band or even when a critical-band noise is used for comparison. The most important parameters influencing sharpness are the spectral content and the centre frequency of narrow-band sounds. In order to give quantitative values, a reference point and a unit have to be defined. In Latin, the expression "acum" is used for sharp. The reference sound producing 1 acum is a narrow-band noise one critical-band wide at a centre frequency of 1 kHz having a level of 60dB. This reference point is marked in Fig. 9.1 E. Zwicker et al., Psychoacoustics © Springer-Verlag Berlin Heidelberg 1999
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Sharpness and Sensory Pleasantness
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Fig. 9.1. Sharpness of critical-band wide narrow-band noise as a function of centre frequency (solid), of band-pass noise with an upper cut-off frequency of 10 kHz as a function of the lower cut-off frequency (broken) and of hand-pass noise with a lower cut-off frequency of 0.2 kHz as a function of the upper cut-off frequency (dotted) . The critical-band rale corresp
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