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Summary

This white paper is structured in 9 chapters, each presenting a quality issue.

Chapter 1 - Audio Quality
Presents a set of definitions and requirements. To support meaningful discussions on audio quality, the concepts ‘quality’, ‘audio’ and ‘sound’ are defined in detail.

Chapter 2 - Networked audio systems
Presents a description of a typical networked (and therefore digital) audio system. The described system is modular, supported by networking technologies that have become common practise in the professional audio field.

Chapter 3 - Performance & Response
Presents the Performance / Response concept - identifying system process parameters and requirements to help assessing the quality of audio systems. Two design philosophies are presented: ‘natural sound’ - where the focus lies on preserving the artistic quality of the audio event and offering Response tools to the sound engineer as variable parameters, and ‘coloured sound’ where a fixed sound-changing Response is designed into products and systems.

Chapter 4 - The human auditory system
Briefly presents a description of the human auditory system, including the mechanics of the outer and middle ear, the bio-mechanical coding to the frequency domain by the inner ear, and the transport of the coded firing patterns to the brain through auditory nerves. Using this description, a ‘human audio universe’ is defined to possess three dimensions: level, frequency and time. Also some auditory functions such as localization and masking are presented.

Chapter 5 - Sampling issues
Presents the audio digitalization (sampling) concept in relation to level, frequency and timing. Dynamic range and frequency range are more or less common concepts, developed to a mature state by the manufacturers of digital audio equipment in the past 25 years. Compared with the 1985 digital (16-bit) technologies, modern 24-bit A/D, D/A and distribution technologies and 32-bit or higher DSP architecture have caused noise floors and distortion levels to move close the boundaries of the audio universe. On timing however, the use of networked audio systems pose new challenges to system designers and sound engineers. This chapter presents the digitalization concept in relation to timing, including latency, jitter and clock phase.

Chapter 6 - Distribution & DSP issues
Presents a description of the transport and DSP infrastructure in a digital audio system. Transport and DSP architecture - eg. bit depth, fixed/floating point processing - are described to have an effect on a system’s audio quality, with only the algorithm (plug-in) design to affect the system’s sound quality.

Chapter 7 - Signal chain level issues
Focuses on audio levels in a system, proposing a ‘0dBFS’ level standard as the optimal design paradigm that allows easy identification of quality problems in a signal chain. Several practical quality issues in system design are presented, such as head amps, gain compensation, clip level mismatch, double pass signal chains. Also, audio compression in speaker processing stage (unbalanced output modes) is discussed, placing the responsibility in the Response (sound quality) domain rather than the Performance (audio quality) domain.

Chapter 8 - operational quality
Presents operational quality issues in a networked audio environment, including topology and protocol and their effect on logistics, reliability and redundancy. The use of ethernet - either as protocol or as embedded service - is posed to be of essential importance to comply with operational quality requirements on design freedom and user interfacing.

Chapter 9 - quality assessment methods
Presents methods for subjective and objective quality assessments of audio systems. Conditions for controlled listening tests are proposed for audio quality assessment. Full control over the experiments with careful adjustment of test equipment and environment, and proper statistical analysis are crucial to obtain meaningful results that justify statements on product and system audio quality and Response characteristics.

Appendix 1 - Subject index & glossary
Lists all topics in this white paper written in italic fonts, including all definitions.

Appendix 2 - Information sources & further reading
Lists information sources and further reading suggestions.


>> 1) Audio Quality

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