Battement (acoustique) | EPFL Graph Search

En physique, le battement est une modulation périodique d'un signal constitué de la superposition de deux signaux de fréquences proches. Le terme est issu de l'acoustique ; en acoustique musicale, le battement est audible lorsque deux cordes ou tuyaux vibrent à des fréquences dont la différence est entre 0,5 et environ. Les battements peuvent être perçus facilement en accordant un instrument capable de notes tenues. Accorder deux notes à l'unisson produit un effet particulier : tant que les deux notes ont des hauteurs voisines mais pas identiques, la différence des fréquences produit un battement ; la note résultante est modulée par un trémolo pendant que les sons interfèrent alternativement de manière constructive puis destructive. Lorsque les notes s'approchent de l'unisson, le battement ralentit puis disparaît. On se sert aussi de ce phénomène pour créer des basses d'orgue avec deux tuyaux deux fois plus courts que le nécessaire légèrement différents, dont le battement à une ving

De l'acoustique des églises en Suisse

Victor Desarnaulds

The existence of the fundamental conflict in churches between the desirable acoustic conditions for music and for speech intelligibility prompted this dissertation. It tackles the subject not only under the acoustical perspective but also in the historical, theological, musicological and architectural aspects. This research studies, initially, how during the past, the liturgy, the acoustical and organizational characteristics of churches supported one or the other of these attributes. The second chapter presents the objective analyses of many Reformed worships and Catholic masses which make it possible to show the conditions and requirements for the current Christian celebrations in Switzerland. The analysis of the church geometrical parameters (volume, height, etc.) and of the results of objective acoustical measurements (reverberation time, background noise and speech intelligibility) of approximately two hundred churches in Switzerland allows to statistically describe their characteristics and to objectively verify the assumptions made in the preceding chapter. Chapter 3 also studies the local or global range of conclusions by the comparison of the results obtained in Switzerland with those published for other countries (synthesis of about 400 churches). The study of the origin and the interaction between Liturgy and Acoustics passes in particular by the analysis of the history of sacred music but especially by the examination of the main methods implemented to improve the acoustics of churches. Chapter 4 presents the historical evolution and the acoustical effectiveness of two types of devices used in churches: acoustic pots and pulpits with their canopies. The position of the various participants does not influence only the listening conditions but also reveals the importance attached to their participation. Chapter 5 examines then the historical evolution and statistical analysis of the current conditions regarding the position of the organ, the spatial arrangements for the seated congregation in churches, as well as the effect of the occupation on reverberation time and speech intelligibility. Chapter 6 concludes with the analysis of the desirable acoustical conditions in current churches, particularly with regard to the architectural, organizational (sound system, assembly arrangement and organ location) and the acoustical parameters (reverberation time, background noise and speech intelligibility). This last analysis is based on a significant bibliographical synthesis and on the comparison, for the sampled churches, of the results for objective measurements with the subjective evaluations obtained by a parishioner's sample survey.

EPFL2002

Binaural beats increase interhemispheric alpha-band coherence between auditory cortices

Marco Solcà

Binaural beats (BBs) are an auditory illusion occurring when two tones of slightly different frequency are presented separately to each ear. BBs have been suggested to alter physiological and cognitive processes through synchronization of the brain hemispheres. To test this, we recorded electroencephalograms (EEG) at rest and while participants listened to BBs or a monaural control condition during which both tones were presented to both ears. We calculated for each condition the interhemispheric coherence, which expressed the synchrony between neural oscillations of both hemispheres. Compared to monaural beats and resting state, BBs enhanced interhemispheric coherence between the auditory cortices. Beat frequencies in the alpha (10 Hz) and theta (4 Hz) frequency range both increased interhemispheric coherence selectively at alpha frequencies. In a second experiment, we evaluated whether this coherence increase has a behavioral aftereffect on binaural listening. No effects were observed in a dichotic digit task performed immediately after BBs presentation. Our results suggest that BBs enhance alpha-band oscillation synchrony between the auditory cortices during auditory stimulation. This effect seems to reflect binaural integration rather than entrainment.

Elsevier2015

Demonstration of Multiple Kerr-Frequency-Comb Generation Using Different Lines From Another Kerr Comb Located Up To 50 km Away

Fatemeh Alishahi, Ahmad Fallahpour, Maxim Karpov, Tobias Kippenberg, Arne Kordts, Martin Hubert Peter Pfeiffer, Lin Zhang

On-chip Kerr frequency combs are potentially promising to enhance many applications because of their broad-band operation and chip-scale integration. Such combs offer various mutually coherent optical carriers that can potentially be used as both coherent light sources and local oscillators in optical communications. In this paper, we experimentally demonstrate multiple Kerr frequency comb generation using different lines from another Kerr comb located up to 50 km away. Different master comb lines after fiber propagation can be individually selected to pump distinct microresonators to generate slave combs with different repetition rates. An approximately 20 kHz linewidth can be obtained for the beat notes of the master and remote slave combs. Furthermore, results show that the linewidths of the slave comb lines almost remain the same as that of the master comb pump. A pump light with an optical signal-to-noise ratio of beyond 23 dB is required for slave comb generation. When serving as local oscillators, the slave comb lines have a smaller variation of frequency error than the comb lines generated by an independent unstabilized laser.

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC2019

De l'acoustique des églises en Suisse

Victor Desarnaulds

EPFL2002