Subject: Language Arts (with choices of integration

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


Robert Conetta




Submitted for the Degree of Doctor of Philosophy




Institute of Sound Recording
Faculty of Arts and Human Sciences
University of Surrey



2011






© Robert Conetta

















This thesis and the work to which it refers are the results of my own efforts. Any ideas, data, images or
text resulting from the work of others (whether published or unpublished) are fully identified as such
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ii
Abstract

The research in this thesis describes the creation and development of a method for the prediction of
1perceived spatial quality. The QESTRAL 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.



1 Quality Evaluation of Spatial Transmission and Reproduction using an Artificial Listener
iii Contents

iv Contents

x List of figures

xiv List of tables

Glossary of terms xvii

xxi Acknowledgements

Chapter 1 – Introduction 1
1.1 The QESTRAL project................................................................................................................ 2
1.2 The development of the QESTRAL model................................................................................. 4
1.2.1 Work packages required to develop the QESTRAL model........................................ 4
1.2.2 The specific aims of this research project and organisation of this thesis................... 5
1.3 Summary and conclusions........................................................................................................... 8

Chapter 2 – Sound quality and spatial quality in the reproduced sound environment 10
2.1 Sound quality in the reproduced sound environment.................................................................. 10
2.1.1 A separate evaluation of spatial quality....................................................................... 11
2.1.2 Sound quality: summary and conclusions.................................................................... 13
2.2 Defining spatial quality for this research project......................................................................... 13
2.2.1 Elicitation experiments................................................................................................ 13
2.2.2 Rumsey’s perceptual hierarchy paradigm................................................................... 14
2.2.2.1 Width........................................................................................................... 14
2.2.2.2 Depth and distance...................................................................................... 15
2.2.2.3 Envelopment................................................................................................ 16
2.2.2.4 Presence....................................................................................................... 17
2.2.2.5 Miscellaneous spatial attributes................................................................... 17
2.2.3 Spatial quality: summary and conclusions.................................................................. 17
2.3 Review of current sound quality models..................................................................................... 18
2.3.1 Method for measurements of perceived audio quality (PEAQ) (ITU-R BS.1387)..... 18
2.3.2 Quality Advisor (QA).................................................................................................. 19
2.3.3 Model created by Choi et al........................................................................................ 19
2.3.4 Models created by George et al................................................................................... 20
2.3.5 Sound quality models: summary and conclusions...................................................... 20
2.4 Summary and conclusions........................................................................................................... 21

Chapter 3 – Methods for the development of the QESTRAL model 23
3.1 QESTRAL model development method...................................................................................... 23
3.2 Calibrating the QESTRAL model using linear regression analysis............................................ 25
3.2.1 Partial least squares regression.................................................................................... 25
3.3 QESTRAL model target specifications....................................................................................... 26
3.4 Spatial audio reproduction systems – selecting a system for this study...................................... 27
3.4.1 Monophonic (1.0)........................................................................................................ 27
3.4.2 2-channel stereophony (stereo).................................................................................... 28
3.4.3 3/2 stereo...................................................................................................................... 28
3.4.4 Other reproduction systems......................................................................................... 30
3.4.5 Spatial audio reproduction systems: summary and conclusions.................................. 30
3.5 Summary and conclusions........................................................................................................... 30


iv Chapter 4 – Review of objective metrics that could be used in the QESTRAL model 32
4.1 Metrics for individual spatial attributes of reproduced sound..................................................... 32
4.1.1 Metrics used by Choisel and Wickelmaier.................................................................. 32
4.1.2 Automatic localisation models.................................................................................... 33
4.1.3 Metrics for measuring envelopment and width........................................................... 34
4.1.4 Spatial attribute metrics: summary and conclusions.................................................... 37
4.2 Metrics used in spatial sound quality models..........................................................