Optimization of Acoustic Noise for Single-Shot Echo-Planar Imaging by Varying Echo Spacing
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Single-shot echoplanar imaging (EPI) sequence is a commonly-used readout scheme for functional magnetic resonance imaging (fMRI). It acquires signal in a short period of time with loud acoustic noise, which could cause discomfort for patients and even pose risk for sensitive populations, as well as confound auditory fMRI studies. Though a variety of attempts have been made toward quiet EPI scans, none has considered both the noise level and the timbre. In this study, we investigated the effect of varying echo spacing and modified gradient waveform on sound pressure level and noise spectral entropy. We then used genetic algorithm to optimize both sound pressure level and spectral entropy for single-shot EPI sequence by varying the duration of each readout unit with a sinusoidal waveform, changing the timbre significantly with increased entropy and reduced loudness. The resulting image quality were also compared with images obtained by standard EPI sequence.Keywords:
Timbre
Pulse sequence
Annoyance
A-weighting
Sound exposure
Sound Quality
Psychoacoustics
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This paper presents basic data on loudness level and loudness along with data obtained by the authors, and describes an application of the idea of masked loudness to perception of music in the presence of noise. It is shown that timbre or sound quality of music is well explained by masked loudness vs frequency characteristic.
Timbre
Sound Quality
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A pair of related tools useful for environmental noise assessment are time-varying psychoacoustic loudness, and an expression of sound pressure level in dB[SPL] weighted dynamically according to the contours of equal loudness rather than the static A-weighting. Conventional weightings applicable to sound pressure (dB[A], etc.) are fixed in spectral shape and intended for use over certain ranges of unweighted sound pressure level. Particularly for sounds with tonal content and within the general level range of the A-weighting, the authors propose a new spectral sound pressure weighting assembled from the Phon values of the complete set of equal-loudness contours calculated for each frequency within the human auditory range. It will be shown that although giving values numerically similar to those of the A-weighting, the dB[EQL] or Equal-Loudness weighting is situation-dependent rather than fixed, and better-represents subjective impressions at all frequencies. Although based on perceived loudnesses, the dB[EQL] sound pressure weighting is not a specific loudness measurement, does not consider critical band formation nor yield masking or psychoacoustic loudness data. Developed from the same basis as psychoacoustic loudness of sounds at different frequencies, the dB[EQL] and time-varying loudness together provide a bridge between conventional and psychoacoustic techniques.
Psychoacoustics
A-weighting
Critical band
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To realize comfortable living environment, it is necessary to reduce the environmental noise according to the suitable environmental noise evaluation index. For considering the environmental noise evaluation index, it is important to know characteristics of loudness evaluation toward long-term noise because the environmental noise was evaluated for long-term. In this study, to investigate the evaluation characteristics, we focused on the distribution of sound pressure level in duration of environmental noise and performed loudness evaluation test using long-term noise by changing the distribution. In the test, four traffic noises in duration of 10 min which loudness was adjusted equality by pre-processing were employed as base sounds. In addition, modified four noises in which the deviation of sound pressure level were increased (the mean value was same as the base sounds) were used as target sounds. Fourteen subjects evaluated the loudness of eight traffic noises immediately after hearing each sound. As a result, it was found that loudness impression toward the target sound was evaluated to as softer than the base sound. Consequently the long-term sound having large deviation of sound pressure level was clarified to be evaluated softer than the sound having small deviation.
Sound exposure
Environmental Noise
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The kantele is a plucked string instrument belonging to the family of zithers that are used in traditional folk music in Finland, Northwest Russia, and the Baltic states. We propose design rules for a kantele that has a higher loudness than traditional models and present acoustical analysis results to confirm the amplification. The guidelines for making a plucked string instrument louder are to increase the string tension, to add more radiating surface area, and to isolate the top plate from the sound-box with an air gap. We investigate the increased string tension analytically, and show the benefits of the enlarged radiating surface and the isolated top plate experimentally, by acoustical measurements. The input force and the resulting SPL are measured in an anechoic chamber at several points around the instrument, and the measured SPL values are converted to loudness estimates using a computational model. All results are compared against similar figures for a traditional kantele. A playability test, where a professional kantele player is asked to play as softly and as loudly, as she/he feels comfortable, reveals how much we have been able to widen the dynamic range. Finally, the effect of the structural modifications on the timbre is evaluated.
Timbre
Anechoic chamber
Tension (geology)
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Octave band
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In this study, we performed two subjective evaluation tests to obtain factors that affect subjective loudness for environmental noise having a certain duration. In the first experiment, a subjective loudness evaluation was performed using road- and rail-traffic noises having durations of 10 min. As the result, rail-traffic noise was evaluated as being softer than road-traffic noise, although LAeq of the rail-traffic noise was larger than that of road-traffic noise. Rail-traffic noise had longer duration of the low sound pressure level (SPL) and a short, higher SPL peak than road-traffic noise, and we concluded that the factor of the subjective loudness difference depended on the difference in the low SPL frequency. In the second experiment, subjective loudness evaluations were performed using road-traffic noise and modified road-traffic noise. In the modification, the SPL frequency of the road-traffic noise was changed to be similar to that of rail-traffic noise. As the result, the modified road-traffic noise was evaluated as being softer than the original road-traffic noise. In summary, the subjective loudness for a certain length of noise was found to be affected by the frequency of the SPL, and when noise has a long, low SPL duration, it is evaluated as being softer.
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In this study, we investigated the influence of the distribution of sound-pressure levels (SPLs) on subjective loudness of environmental noise. To investigate the influence, subjective-loudness evaluation test was performed using road-traffic noise having various distributions of SPL. Skewness was used to evaluate the SPL distribution. Our results show that the loudness of the presented sound was perceived to be softer when the skewness was largest at 0.8 (the frequency of low SPL was high), even though the equivalent continuous A-weighted sound-pressure level (LAeq) was almost the same for all samples. On the other hand, the subjective loudness did not change significantly in the other conditions (the frequency of low SPL was low). From the result, the subjective loudness was found to decrease at a specific condition when the frequency of low SPL is high.
Sound exposure
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This study investigated the effects of differing loudness levels on discrimination of pitch, rhythm, duration, loudness, timbre, and tonal memory. Subjects were 101 university undergraduates, and comparisons were made for music versus nonmusic majors, males versus females, and those with exposure versus nonexposure to loud sounds. Analysis of variance procedures revealed the significant influence of varying loudness levels on rhythm, duration, loudness, and timbre discriminations. Music and nonmusic majors responded similarly, though several interactions were noted. No major differences appeared concerning the sex variable nor the exposure to loudness grouping; however, the nonexposure subjects fared more favorably in a preponderance of mean data comparisons (15 of 21)— a trend most marked among the nonmusic majors. Implications were that less intense presentation levels should be employed to enhance timbre discriminations, louder presentation levels to enhance perception and discrimination of loudness or dynamic variation. Also noted was the need to view cautiously those test norms and results acquired without rigorous control of loudness presentation levels.
Timbre
Presentation (obstetrics)
Variation (astronomy)
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The noises in the driver's cab and the carriage of a high-speed train are measured respectively at different speeds on site.By using the linear sound pressure level,A-weighted sound pressure level and specific loudness,the spectrum characteristics of the measured interior noises at 330km/h are analyred and the dominant frequency ranges are identified.Objective evaluation of the measured interior noises are carried out in respect of the sound quality of loudness,sharpness,roughness and fluctuation strength based on the psycho-acoustical theory.The research results indicate as follows:Analysis of the specific loudness accurately characterizes the frequency components which induce changes in loudness to the feeling of human ears;The loudness of interior noises at all measure points enhances coutinuously with increasing of the train speed,especially in the cab,the front car of the train,Which is under intensified aerodynamic effect;Loudness assessment tells that the interior acoustic environment of the high speed train needs to be further improved to satisfy the requirements of passengers for acoustic comfort,especially in the cab and at the position of the centre plates of the carriage where appropriate measures should be taken to reduce vibration and noises.
Sound Quality
High speed train
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