Technical sounds often contain several tonal components, forming a multi-tone sound. The present study investigates the perception of multi-tone sounds consisting of two harmonic complexes with different fundamental frequencies and combination tones with frequencies that are equal to the sum of multiple integers of the two fundamentals. The experimental parameter is the ratio between the two fundamental frequencies ρ. A total of 15 synthetic multi-tone sounds are rated by 37 participants. In the first experiment, the perceptual space is assessed based on 16 adjective scales using categorical scaling. The resulting perceptual space has the four dimensions (i) pleasant, (ii) power, (iii) temporal structure, and (iv) spectral content of the sounds. In the second experiment, the pleasantness is measured with a paired comparison test. The data consistently show that sounds based on ratios of small integers (e.g., ρ=4:3) are significantly less pleasant than sounds with ratios based on large integers which were constructed by a slight detuning from a ratio of small integers. The repetition rate derived from an autocorrelation analysis of the stimuli turns out to be a good predictor of the (un-)pleasantness sensation.
In a previous study by the authors, two indices were identified as appropriate descriptors for perceptual dimensions of fan noise. The index Nlow describes the amount of low-frequency loudness relative to the overall loudness. The index Nratio represents the ratio between the amount of loudness resulting from mid-frequency content and that from high frequencies. The aim of this study is to quantify how variations in these two indices affect subjects' preferences and loudness judgments. In listening experiments, fan noise signals were adjusted separately to equal loudness and equal preference compared to a common reference sound by varying their level in an adaptive procedure. The fan noises used in the listening tests consisted of 11 typical signals from three major groups of fan sounds from the earlier study and 18 signals that were parametrically varied in terms of the two indices. Reductions in A-weighted sound pressure level of up to 15 dB were necessary to make unpleasant fan sounds equally preferred as the fixed reference sound. A regression model based on the index Nratio explains 81% of the variation in the evaluation data with a root-mean-squared error of 2.53 dB.
In the assessment of noise annoyance and sound quality, judgments made in the laboratory can be influenced by the prior experience that a participant had with the specific type of sound under test. In field tests for noise annoyance, prior experience and individual noise sensitivity
are often part of the data collection but they are not always reported for sound quality evaluations in the laboratory. In this paper, data from listening tests dealing with the perception of fan noise was re-analyzed with respect to the individual prior experience participants had with fan
noise in their life. The answers to a short questionnaire showed that the prior experience of the participants with fan sounds was quite different. For the investigated 30 fan sounds, five categories of every-day situations could be identified, in which fan sounds had been most commonly heard
by the participants. The frequency how often fan sounds had been heard and the overall annoyance by fan sounds in daily life differed considerably between the participants. However, the exploration of the present data did not reveal a strong link between the individual prior experience and
the results of the listening tests when averaged across participants with same ratings.
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