Audio system measurements | EPFL Graph Search

Audio system measurements are a means of quantifying system performance. These measurements are made for several purposes. Designers take measurements so that they can specify the performance of a piece of equipment. Maintenance engineers make them to ensure equipment is still working to specification, or to ensure that the cumulative defects of an audio path are within limits considered acceptable. Audio system measurements often accommodate psychoacoustic principles to measure the system in a way that relates to human hearing. Subjectivity and frequency weighting Subjectively valid methods came to prominence in consumer audio in the UK and Europe in the 1970s, when the introduction of compact cassette tape, dbx and Dolby noise reduction techniques revealed the unsatisfactory nature of many basic engineering measurements. The specification of weighted CCIR-468 quasi-peak noise, and weighted quasi-peak wow and flutter became particularly widely used and attempts were made

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

Timing jitter studies of the SwissFEL Test Injector drive laser

Christoph Peter Hauri, Thomas Schietinger

To produce short X-ray pulses for SwissFEL(1), it is necessary to compress the electron bunches by a factor of 300, down to sub-fs for the attosecond operational modes. To achieve stable EEL output accurate timing of the initial electron injection at the main linear accelerator is necessary. Tolerance studies show, that to reach the final performance goals, less than 40 fs relative rms jitter is required from the electron gun, relative to the reference. Here we present independent residual RF phase noise measurements of the laser oscillators, showing an exceptional similar to 30 fs integrated rms jitter. Moreover timing studies at the SwissFEL Injector Test Facility, based on charge detection at the sharp rising edge of the Schottky-scan were performed allowing for systematic correlation studies and showing a residual jitter of similar to 150 fs at 10 Hz from the pulsed laser system and beam transport respect to the reference. For future development, available relative jitter measurement techniques for pulsed laser systems will be reviewed and their applicability for laser arrival time monitoring and feedback for EEL applications will be discussed. (C) 2013 Published by Elsevier B.V.

Elsevier Science Bv2014

De l'acoustique des églises en Suisse

Victor Desarnaulds

EPFL2002