Blind estimation of reverberation time in classrooms and hospital wards

This paper investigates blind Reverberation Time (RT) estimation in occupied classrooms and hospital wards. Measurements are usually made while these spaces are unoccupied for logistical reasons. However, occupancy can have a significant impact on the rate of reverberant decay. Recent work has developed a Maximum Likelihood Estimation (MLE) method which utilises only passively recorded speech and music signals, this enables measurements to be made while the room is in use. In this paper the MLE method is applied to recordings made in classrooms during lessons. Classroom occupancy levels differ for each lesson, therefore a model is developed using blind estimates to predict the RT for any occupancy level to within ±0.07s for the mid-frequency octave bands. The model is also able to predict the effective room and per person absorption area. Ambient sound recordings were also carried out in a number of rooms in two hospitals for a week. Hospital measurements are more challenging as the occurrence of free reverberant decay is rarer than in schools and the acoustic conditions may be non-stationary. However, by gaining recordings over a period of a week, estimates can be gained within ±0.07 s. These estimates are representative of the times when the room contains the highest acoustic absorption. In other words when curtains are drawn, there are many visitors or perhaps a window may be open

Towards the automatic assessment of spatial quality in the reproduced sound environment

The research in this thesis describes the creation and development of a method for the prediction of perceived spatial quality. The QESTRAL (Quality Evaluation of Spatial Transmission and Reproduction using an Artificial Listener) model is an objective evaluation model capable of accurately predicting changes to perceived spatial quality. It uses probe signals and a set of objective metrics to measure changes to low-level spatial attributes. A polynomial weighting function derived from regression analysis is used to predict data from listening tests, which employed spatial audio processes (SAPs) proven to stress those low-level attributes. A listening test method was developed for collecting listener judgements of impairments to spatial quality. This involved the creation of a novel test interface to reduce the biases inherent in other similar audio quality assessment tests. Pilot studies were undertaken which established the suitability of the method. Two large scale listening tests were conducted using 31 Tonmeister students from the Institute of Sound Recording (IoSR), University of Surrey. These tests evaluated 48 different SAPs, typically encountered in consumer sound reproduction equipment, when applied to 6 types of programme material. The tests were conducted at two listening positions to determine how perceived spatial quality was changed. Analysis of the data collected from these listening tests showed that the SAPs created a diverse range of judgements that spanned the range of the spatial quality test scale and that listening position, programme material type and listener each had a statistically significant influence upon perceived spatial quality. These factors were incorporated into a database of 308 responses used to calibrate the model. The model was calibrated using partial least-squares regression using target specifications similar to those of audio quality models created by other researchers. This resulted in five objective metrics being selected for use in the model. A method of post correction using an exponential equation was used to reduce non-linearity in the predicted results, thought to be caused by the inability of some metrics to scrutinise the highest quality SAPs. The resulting model had a correlation (r) of 0.89 and an error (RMSE) of 11.06% and performs similarly to models developed by other researchers. Statistical analysis also indicated that the model would generalise to a larger population of listeners.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The impact of classroom noise on reading comprehension of secondary school pupils

It has been known for many years that poor acoustic conditions in classrooms leading to high noise levels and poor speech intelligibility cause annoyance to pupils and teachers and affect the academic performance of pupils. Much of the previous research concerning the impact of noise and poor acoustics on pupils has involved children in primary schools, with fewer studies related to pupils of secondary school age. Furthermore, the majority of previous studies in schools have examined the impact of environmental noise, particularly aircraft noise, on children. The aim of the study described here was to examine the effects of typical levels of classroom noise on secondary school pupils, and to attempt to identify the threshold level at which adverse impacts might occur. A survey of acoustic conditions in secondary schools in England1 was accompanied by questionnaire surveys of pupils to ascertain levels of annoyance caused by noise, and their perceptions of its interference with their ability to hear and understand their teachers2 . In addition, students were tested in numeracy, mathematical reasoning, memory and reading comprehension in different levels of classroom noise. This paper describes the results of reading comprehension tests undertaken by nearly 1000 pupils aged between 11 and 16 years while they were exposed to typical classroom noise at different levels

A survey of acoustic conditions and noise levels in secondary school classrooms in England

An acoustic survey of secondary schools in England has been undertaken. Room acoustic parameters and background noise levels were measured in 185 unoccupied spaces in 13 schools to provide information on the typical acoustic environment of secondary schools. The unoccupied acoustic and noise data were correlated with various physical characteristics of the spaces. Room height and the amount of glazing were related to the unoccupied reverberation time and therefore need to be controlled to reduce reverberation to suitable levels for teaching and learning. Further analysis of the unoccupied data showed that the introduction of legislation relating to school acoustics in England and Wales in 2003 approximately doubled the number of school spaces complying with current standards. Noise levels were also measured during 274 lessons to examine typical levels generated during teaching activities in secondary schools and to investigate the influence of acoustic design on working noise levels in the classroom. Comparison of unoccupied and occupied data showed that unoccupied acoustic conditions affect the noise levels occurring during lessons. They were also related to the time spent in disruption to the lessons (e.g., students talking or shouting) and so may also have an impact upon student behavior in the classroom

Towards the automatic assessment of spatial quality in the reproduced sound environment

The research in this thesis describes the creation and development of a method for the prediction of perceived spatial quality. The QESTRAL (Quality Evaluation of Spatial Transmission and Reproduction using an Artificial Listener) model is an objective evaluation model capable of accurately predicting changes to perceived spatial quality. It uses probe signals and a set of objective metrics to measure changes to low-level spatial attributes. A polynomial weighting function derived from regression analysis is used to predict data from listening tests, which employed spatial audio processes (SAPs) proven to stress those low-level attributes. A listening test method was developed for collecting listener judgements of impairments to spatial quality. This involved the creation of a novel test interface to reduce the biases inherent in other similar audio quality assessment tests. Pilot studies were undertaken which established the suitability of the method. Two large scale listening tests were conducted using 31 Tonmeister students from the Institute of Sound Recording (IoSR), University of Surrey. These tests evaluated 48 different SAPs, typically encountered in consumer sound reproduction equipment, when applied to 6 types of programme material. The tests were conducted at two listening positions to determine how perceived spatial quality was changed. Analysis of the data collected from these listening tests showed that the SAPs created a diverse range of judgements that spanned the range of the spatial quality test scale and that listening position, programme material type and listener each had a statistically significant influence upon perceived spatial quality. These factors were incorporated into a database of 308 responses used to calibrate the model. The model was calibrated using partial least-squares regression using target specifications similar to those of audio quality models created by other researchers. This resulted in five objective metrics being selected for use in the model. A method of post correction using an exponential equation was used to reduce non-linearity in the predicted results, thought to be caused by the inability of some metrics to scrutinise the highest quality SAPs. The resulting model had a correlation (r) of 0.89 and an error (RMSE) of 11.06% and performs similarly to models developed by other researchers. Statistical analysis also indicated that the model would generalise to a larger population of listeners

Envelopment: What is it? A definition for multichannel audio

The spatial attribute envelopment has long been considered an important property of excellent concert hall acoustics. In the past, research in this area has produced the definition listener envelopment (LEV) and several equations designed to predict it. However with the recent development of multichannel audio systems capable of positioning sound sources all around the listener, it is apparent that the attribute is not so easily defined and that a more appropriate definition may be needed. This poster introduces a definition of envelopment more appropriate for multichannel audio and outlines a recent pilot experiment conducted by the authors

Estimates of perceived spatial quality across the listening area

This paper describes a computational model for the prediction of perceived spatial quality for reproduced sound at arbitrary locations in the listening area. The model is specifically designed to evaluate distortions in the spatial domain such as changes in source location, width and envelopment. Maps of perceived spatial quality across the listening area are presented from our initial results

Envelopment: What is it? A definition for multichannel audio

The spatial attribute envelopment has long been considered an important property of excellent concert hall acoustics. In the past, research in this area has produced the definition listener envelopment (LEV) and several equations designed to predict it. However with the recent development of multichannel audio systems capable of positioning sound sources all around the listener, it is apparent that the attribute is not so easily defined and that a more appropriate definition may be needed. This poster introduces a definition of envelopment more appropriate for multichannel audio and outlines a recent pilot experiment conducted by the authors

Estimates of perceived spatial quality across the listening area

This paper describes a computational model for the prediction of perceived spatial quality for reproduced sound at arbitrary locations in the listening area. The model is specifically designed to evaluate distortions in the spatial domain such as changes in source location, width and envelopment. Maps of perceived spatial quality across the listening area are presented from our initial results