Critical Band Rate Research Articles

Assessment of Drone Noise Within Urban Soundscapes

Drones have the potential to be implemented in the infrastructure of metropolitan areas to provide services to the public such as delivery, maintenance, and even blue light services. The scope for drone capability is large, but this comes with the risk of introducing a dominant, unpleasant noise source above urban areas, with potentially adverse health effects. This paper describes research which investigates whether, and to what extent, different urban soundscapes mask noise from drone operations, and using statistical analysis methods such as principal component analysis interrogates which frequency ranges of drone noise should be appropriately masked to reduce perceived annoyance. A subjective experiment was carried out, where participants gave response values to a comprehensive set of drone sounds embedded into differing urban soundscapes. Response values included perceived annoyance, perceived loudness, drone noise dominance and soundscape pleasantness. Critical-band rate specific sound quality metrics were then calculated for the soundscapes with and without each drone sound present, and the metric value differences were used in principle component analysis, with the results suggesting which specific sound quality metrics contribute significantly to the response values.

Single-Channel Speech Enhancement Using Critical-Band Rate Scale Based Improved Multi-Band Spectral Subtraction

This paper addresses the problem of single-channel speech enhancement in the adverse environment. The critical-band rate scale based on improved multi-band spectral subtraction is investigated in this study for enhancement of single-channel speech. In this work, the whole speech spectrum is divided into different non-uniformly spaced frequency bands in accordance with the critical-band rate scale of the psycho-acoustic model and the spectral over-subtraction is carried-out separately in each band. In addition, for the estimation of the noise from each band, the adaptive noise estimation approach is used and does not require explicit speech silence detection. The noise is estimated and updated by adaptively smoothing the noisy signal power in each band. The smoothing parameter is controlled by a-posteriori signal-to-noise ratio (SNR). For the performance analysis of the proposed algorithm, the objective measures, such as, SNR, segmental SNR, and perceptual evaluations of the speech quality are conducted for the variety of noises at different levels of SNRs. The speech spectrogram and objective evaluations of the proposed algorithm are compared with other standard speech enhancement algorithms and proved that the musical structure of the remnant noise and background noise is better suppressed by the proposed algorithm.

Acoustical topology optimization for Zwicker’s loudness model – Application to noise barriers

Traditionally, the objective of design optimization of an acoustic system is to reduce physical acoustic properties, i.e., sound pressure and power. However, since these parameters are not sufficient to present the relation of physical sound stimulus with human perceptual judgment, physical acoustic properties may not represent adequate parameters for optimizing acoustic devices. In this paper, we first present a design method for acoustical topology optimization by considering human’s subjective conception of sound. To consider human hearing characteristics, Zwicker’s loudness is calculated according to DIN45631 (ISO 532B). The main objective of this work is to minimize the main specific loudness of a target critical band rate by optimizing the distribution of the reflecting material in a design domain. The Helmholtz equation is used to model acoustic wave propagation and, it is solved using the finite element method. The sensitivity of the main specific loudness is calculated using the adjoint variable method and the chain rule. To demonstrate the effectiveness of the proposed method, various examples of noise barriers are presented with different source and receiver locations. The results obtained, using the optimized noise barriers that consider Zwicker’s loudness, are compared with the results for straight and T-shaped barriers. The results are also compared with topology optimization using 1/3-octave band level as an objective function. The optimized noise barrier using the proposed method shows the best result with respect to a human’s hearing sensation.

Efficient Individualization Method of HRTFs Using Critical-band Based Spectral Cue Control

Recently, 3-D audio technologies are commonly implemented through headphones. A major problem of the headphone-based 3-D audio is in-the-head localization, which occurs due to the inaccurate Head-Related Transfer Function (HRTF). Since the individual measurements of HRTFs are impractical, there have been several researches for HRTF customization. In this paper, an efficient method of customizing HRTFs for the sound externalization is proposed. Firstly, it is determined which part will be customized in HRTF through psychoacoustical experiments. Then, the method controlling spectral notches and envelopes to provide individual localization cues are described. Since the proposed method is based on a critical-band rate, the structure is much simpler than that of previous studies, but still effective. The performance was evaluated through a series of subjective tests, and the results confirmed that the customized HRTF using proposed method could replace the measured individual HRTF successfully.

The Perception of Fricative Peaks and Noise Bands

Recent work on the identification and perception of fricatives has focussed on the use by listeners of spectral moments derived from the whole spectrum and there appears to be no work in the literature on the use of prominent spectral peaks. In this study, we map the response of a single listener to narrow bands of noise that "mimic" the spectral peaks of English voiceless fricatives. The stimuli are based on the critical-band rate scale (Zwicker and Fastl, 1990) which divides the audible frequency range up to 15,500 Hz into 24 abutting critical bands. The results suggest that listeners have knowledge that enables them to connect a narrow-band spectral peak with a particular fricative consonant. We demonstrate that such knowledge, particularly in conjunction with a normalization metric that takes account of an individual speaker's vocal tract characteristics (F0 of the vowel following the fricative), could be used to good effect, particularly in noisy conditions which impair the use of the whole spectrum.

A loudness model in dichotic conditions

Existing loudness models are specified only to diotic sounds in spite of the fact that normal human beings hear dichotic sounds. The arithmetic mean of loudness values of both ear signals has been suggested for the approximated value of the resultant perceived loudness. In this study, the dependence of overall loudness perception on the interaural level differences was investigated by the subjective tests. It was found that the larger the interaural level difference, the louder the perception than the mean of calculated loudness values at both ears and the lower the critical band rate or the reference level, the louder the perception than the mean value. A modified loudness model was proposed for the application to dichotic sounds by using the equivalent diotic levels.

Sex-specific fundamental and formant frequency patterns in a cross-sectional study.

An extensive developmental acoustic study of the speech patterns of children and adults was reported by Lee and colleagues [Lee et al., J. Acoust. Soc. Am. 105, 1455-1468 (1999)]. This paper presents a reexamination of selected fundamental frequency and formant frequency data presented in their report for ten monophthongs by investigating sex-specific and developmental patterns using two different approaches. The first of these includes the investigation of age- and sex-specific formant frequency patterns in the monophthongs. The second, the investigation of fundamental frequency and formant frequency data using the critical band rate (bark) scale and a number of acoustic-phonetic dimensions of the monophthongs from an age- and sex-specific perspective. These acoustic-phonetic dimensions include: vowel spaces and distances from speaker centroids; frequency differences between the formant frequencies of males and females; vowel openness/closeness and frontness/backness; the degree of vocal effort; and formant frequency ranges. Both approaches reveal both age- and sex-specific development patterns which also appear to be dependent on whether vowels are peripheral or nonperipheral. The developmental emergence of these sex-specific differences are discussed with reference to anatomical, physiological, sociophonetic, and culturally determined factors. Some directions for further investigation into the age-linked sex differences in speech across the lifespan are also proposed.

A measure for predicting audibility discrimination thresholds for spectral envelope distortions in vowel sounds.

Both in speech synthesis and in sound coding it is often beneficial to have a measure that predicts whether, and to what extent, two sounds are different. This paper addresses the problem of estimating the perceptual effects of small modifications to the spectral envelope of a harmonic sound. A recently proposed auditory model is investigated that transforms the physical spectrum into a pattern of specific loudness as a function of critical band rate. A distance measure based on the concept of partial loudness is presented, which treats detectability in terms of a partial loudness threshold. This approach is adapted to the problem of estimating discrimination thresholds related to modifications of the spectral envelope of synthetic vowels. Data obtained from subjective listening tests using a representative set of stimuli in a 3IFC adaptive procedure show that the model makes reasonably good predictions of the discrimination threshold. Systematic deviations from the predicted thresholds may be related to individual differences in auditory filter selectivity. The partial loudness measure is compared with previously proposed distance measures such as the Euclidean distance between excitation patterns and between specific loudness applied to the same experimental data. An objective test measure shows that the partial loudness measure and the Euclidean distance of the excitation patterns are equally appropriate as distance measures for predicting audibility thresholds. The Euclidean distance between specific loudness is worse in performance compared with the other two.

Prediction of speech transmission quality of wideband and narrow-band telephone handsets using short-time sub-band analysis and psychoacoustic models

A predictor is presented which estimates the mean opinion score (MOS) for a given speech sample from speech and noise transfer characteristics of a specific handset applied to an artificial ear. The critical band rate excitation pattern is computed in 50-ms blocks for original and distorted speech signals and additive room noise. For each block three psychoacoustic parameters are computed: An intelligibility index (I) is evaluated using SNR analysis in each sub-band and considering simultaneous masking effects. Naturalness (N) is estimated by spectral distance between original and distorted speech. A loudness index (L) is derived from loudness (computed similar to ISO532) using a trapezoid function: L decreases if the loudness which is exceeded in 10% of time is lower than 15 sone or higher than 45 sone. The MOS is predicted as a weighted sum of I, N, and L. The prediction results were verified by an opinion test including totally 442 speech samples of several talkers which were filtered simulating typical transfer characteristics of handsets and presented in a noisy environment. Speech level and SNR were varied in a wide range. The comparison proves a good correlation (p=0.93 for all samples and p=0.96 for speech levels below 76 dB SPL).

On the frequency separation of simultaneously evoked otoacoustic emissions’ consecutive extrema and its relation to cochlear traveling waves

Simultaneously evoked otoacoustic emissions (SEOAEs) were recorded in 24 ears of 17 normal-hearing subjects. The data are pooled as frequency separations between neighboring maxima expressed in critical-band rate. The distribution shows a clear maximum at 0.4 Bark corresponding to a distance of about 0.5 mm along the basilar membrane. This characteristic value is discussed using related data from an analog model of nonlinear cochlear preprocessing with active feedback and lateral coupling. Results indicate that the phase characteristic of the traveling wave in the cochlea has a slope of 180° per 0.4 Bark (0.5 mm) near the respective characteristic place. A frequency shift corresponding to a traveling-wave-place shift of 0.5 mm results in an SEOAE-phase shift of two times 180°, i.e., 360° phase shift, as found for neighboring SEOAE maxima or minima.

Articulatory and perceptual factors controlling the age- and sex-conditioned variability in formant frequencies of vowels

Speech sounds, as heard by listeners, contain phonetic, personal, and transmission information. The differences between the formant frequencies of vowels spoken by men, women, and children show a fairly uniform tendency in several studies and languages, and they are regarded as personal quality differences. The differences between the sexes are mainly due to the descent of the larynx in males during puberty. The observed tendency in female/male formant frequency ratios is reproduced in a calculation taking into account the physiological consequences of larynx descent and assuming that the vowel specific neural commands to the articulators remain unchanged. The perception of phonetic quality is seen as a process of tonotopic gestalt recognition. The tonality (= critical-band rate) distances between the formants in phonetically identical vowels are claimed and shown to be invariant as long as they are smaller than 6 Bark. The absolute position of the formants allows personal variation. The tonality distance between the first formant and the fundamental is smaller in most vowels spoken by women than in those by men and children. As for the role of the fundamental in this connection, some alternative hypotheses are discussed.

Analytical expressions for critical-band rate and critical bandwidth as a function of frequency

The critical-band rate as well as the critical bandwidth are functions of frequency. These dependencies have been given in table form. For effective use of these values in computers, relatively simple equations are given to express the dependence of critical-band rate on frequency with an accuracy better than 0.2 Bark and that of critical bandwidth on frequency with an accuracy better than 10% over the whole auditory range.