Vincent Koehl

Influence of Train Colour on Loudness Judgments

This study replicates an experiment described by Patsouras et al. [5] or Rader et al. [8] in which subjects had to evaluate the loudness of a passing-by train noise while watching pictures of the train, the colour of which being varied. In contrast to these studies, no influence of train colour on loudness evaluation could be found. This discrepancy might be due to cultural differences (French subjects vs. German or Japanese ones). But a more realistic reason can be a jury sampling effect, as this influence can exist for very few subjects (one among twenty-two in this experiment).

Loudspeaker sound quality: comparison of assessment procedures

In listening tests involving different loudspeakers and aimed at assessing the sound quality of these sound‐reproducing systems, the level is generally adjusted to compensate for differences in sensitivity. The loudness sensation must be alike for each system under test. Because of the non‐stationary nature of the musical signals used as test material in loudspeaker ratings, loudness assessment by using the current models (Zwicker, Mooreœ) remains slightly inaccurate. In practice, loudness is often equalized by ear by the experimenter. This study deals with the comparison of various test procedures. The first experiment was a paired comparison of loudspeakers where short‐duration stimuli were presented to listeners for preference ratings. In the second experiment, the same listeners were allowed to switch, at any time, from one loudspeaker to another one so that the proposed stimuli were longer. In both experiments the loudness was equalized by the experimenter. However, under normal listening conditions,...

Loudness of low-frequency pure tones lateralized by interaural time differences

Directional loudness is that phenomenon by which the loudness of a sound may vary according to the localization of its source. This phenomenon has been mainly observed for high-frequency sounds, for sources located in the horizontal plane. Because of the acoustic shadow of the head, the left and right ear pressures are modified depending on the source azimuth and the global loudness resulting from a summation process may vary accordingly. Directional loudness has also been reported to occur at 400 Hz, where shadowing effects are usually rather small. It might therefore be suspected that directional loudness effects could be influenced by other parameters involved in the localization process. This study assessed the loudness of low-frequency pure tones (200 and 400 Hz) lateralized with headphones by applying an interaural time difference (ITD) but no interaural level difference. It showed small but significant variations of loudness with respect to ITD at a low loudness level (40 phon): ITD values associated with virtual azimuths of ±60° and ±90° led to a small but significant increase in loudness (up to 1.25 dB). However, there was no such effect at a moderate loudness level (70 phon).

Effects of interaural differences on the loudness of low-frequency pure tones

The loudness related to a sound may vary according to the localization of its source. This phenomenon is described as directional loudness and has been mainly observed for high-frequency sounds and for sources located in the horizontal plane. Because of the acoustic shadow of the head, the left and right ear pressures are modified depending on the source azimuth and the global loudness resulting from a summation process may vary accordingly. But directional loudness has also been reported to occur at 400 Hz, where shadowing effects are usually rather small. It might therefore be suspected that directional loudness effects could be influenced by other parameters involved in the localization process. In a previous study, a small but significant increase of loudness with increasing interaural time difference (ITD) was shown for low-frequency pure tones (200 and 400 Hz) at a low loudness level (40 phon). The present study aimed at getting insight into the potential cause and extent of this effect by assessing the loudness of similar pure tones lateralized with headphones by applying an interaural level difference (ILD) in addition to an ITD and by measuring the effect of ITD at the hearing threshold. It showed significant effects of both ILD and ITD on loudness, and no interaction between these factors. As the effects added even when the factors were contradictory, it supports the hypothesis that the effect is caused by the ITD itself and is not related to the localization process. However, the ITD effect was not significant at the hearing threshold.

Effects of headphone transfer function scattering on sound perception

This study aims at evaluating the audibility of spectral modifications induced by slight but realistic changes in the headphone position over a listeners ears. Recordings have been performed on a dummy head on which 2 different headphone models were placed 8 times each. Music excerpts and pink noise were played over the headphones and recorded with microphones located at the entrance of the blocked ear canal. These recordings were then presented to expert and naïve listeners over a single test headphone. The subjects had to assess the recordings in a 3I3AFC task to discriminate between the different headphone positions. With the exception of one music excerpt for naïve listeners only, subjects were able to discriminate between the headphone positions.

Influence of interaural time differences on loudness for low-frequency pure tones at varying signal and noise levels

Directional loudness sensitivity, which is generally accounted for by at-ear pressure modifications because of the perturbation of the sound field by the head, has been reported to occur at 400 Hz where shadowing effects are usually considered small. Then, an effect of the interaural time difference (ITD) on loudness has been observed for pure tones below 500 Hz. The latter was rather small but still significant, contributing to directional loudness sensitivity. In addition, it has been shown that the effect of ITD on loudness was caused by the ITD itself and not by its related localization. As this effect appeared significant at low level only (40 phon), it was hypothesized that ITD could help separate the signal from the internal noise and enhance its loudness. The aim of the present study is to confirm this hypothesis by observing the effect of ITD on the loudness of low-frequency pure tones (100 and 200 Hz) for various signal-to-noise ratios. The signal level was varied from 30 to 90 phon and the nois...

Effect of the interaural time difference on the loudness of pure tones as a function of the frequency

Significant loudness variations with source azimuth (i.e. directional loudness) are generally accounted for by at-ear pressure modifications. An effect of the interaural time difference (ITD) was also reported in previous studies by the authors: the loudness of pure tones (200 and 400 Hz) significantly increased when the stimuli were presented with an ITD of 772 μs, corresponding to an azimuth of 90°. The present study aims at observing this effect for higher frequencies, including frequencies at which ITD is no longer useful as a localization cue. The effect of ITD on the loudness of pure tones was thus studied at 500, 707, 1000, 1404 and 2000 Hz. Results show that the effect of ITD on loudness is not significant above 500 Hz, even for frequencies where ITD is still a localization cue. The effect observed at 500 Hz is still in agreement with the results reported by previous studies as the loudness of a pure tone significantly increases when its ITD is 772 μs.

Impact of spatial audiovisual coherence on source unmasking

The influence of the spatial audiovisual coherence is evaluated in the context of a video recording of live music. In this context, audio engineers currently balance the audio spectrum to unmask each music instrument getting it intelligible inside the stereo mix. In contrast, sound engineers using spatial audio technologies have reported that sound source equalization is unnecessary in live music mixing when the sound sources are played at the same location of the physical instruments. The effects of spatial audiovisual coherence and sound spatialization have been assessed: expert subjects were asked to compare two mixes in audio only and in audiovisual mode. For this aim, music concerts were visually projected and audio rendered using WFS. Three sound engineers did the audio mixing for all pieces of music in the same room were the test have been carried out.

Effect of drone reed material on great highland bagpipe sound

Great highland bagpipe drones are equipped with single beating reeds. These reeds were traditionally made of cane but more and more musicians nowadays use synthetic reeds. The advantage of synthetic reed is its reduced dependance on air moisture and temperature as well as its increased stability with aging. Despite this advantage, many musicians consider that equipping their instrument with synthetic reeds would degrade its timbre and remain faithful to cane reeds. In the present study, the sound of drones equipped with cane or plastic reeds was first recorded. Expert listeners were then asked to assess these recordings with respect to the following attributes : global quality of sound, clarity, aggressiveness, warmth, volume and immersion. The reed material appeared to be without significant effect on the global quality of drone sound (and also on other perceptual attributes), when one tenor or bass drone was played alon e, and when the two tenor drones and the bass drone were played with the chanter (full set). However, independently of the material, some reeds obtained higher ratings than some other ones. Global Quality was correlated with warmth, immersion and clarity (to a lesser extent with aggressiveness)in full set condition. Correlations between perceptual results and signal analyses showed, about tenor drones, that listeners appreciated sounds having a fundamental frequency with a large magnitude, and less energy for higher harmonics. The analysis of the material influence on these signal properties indicated that synthetic tenor reeds should obtained higher quality ratings (even if this effect was not significant according to the statistical analysis).

Ventriloquism effect with sound stimuli varying in both azimuth and elevation

When presented with a spatially discordant auditory-visual stimulus, subjects sometimes perceive the sound and the visual stimuli as coming from the same location. Such a phenomenon is often referred to as perceptual fusion or ventriloquism, as it evokes the illusion created by a ventriloquist when his voice seems to emanate from his puppet rather than from his mouth. While this effect has been extensively examined in the horizontal plane and to a lesser extent in distance, few psychoacoustic studies have focused on elevation. In the present experiment, sequences of a man talking were presented to subjects. His voice could be reproduced on different loudspeakers, which created disparities in both azimuth and elevation between the sound and the visual stimuli. For each presentation, subjects had to indicate whether the voice seemed to emanate from the mouth of the actor or not. Results showed that ventriloquism could be observed with larger audiovisual disparities in elevation than in azimuth.