CARACTERIZACIÓN GENETICA DE LOS PACIENTES AF

Current use of 5.1 surround sound in broadcast is likely to be predominant for some time to come as broadcasters and broadcast manufacturers have invested substantially in infrastructure developed around these formats. Test broadcast in Japan utilizing a 22.2 audio system suggest that an increased number of channels may be one route forward as high bandwidth connectivity becomes more widespread. Any such system would

certainly be accompanied by similar metadata that could be utilized in the same way as any accessible audio system developed for 5.1. Another possibility is that object based audio may replace channel based audio as a broadcast audio standard. Object based audio treats individual sound sources as discrete objects with coordinate locations, regardless of reproduction system, and developments from companies like DTS, Fraunhofer, Dolby and others suggest that this may become more mainstream although not in the short term. This is covered in more depth in chapter 7 of this thesis.

2.4.

Psychoacoustic Test Methodology

In order to design appropriate test methods to assess the viability and effectiveness of processes and conditions for TV audio it is firstly important to be clear on definitions of what is being assessed. At this stage a distinction is drawn between intelligibility of speech and clarity of speech. Within this thesis the term ‘clarity’ is defined as perceived clarity, i.e. a measure of how clear the speech appears to be to a listener. Intelligibility will be used to refer to a measure of how well speech can be understood and assessed either by correct identification of words or by comprehension of the meaning of phrases or sentences. Although there are clear similarities between these terms and many

instances in literature where each are used interchangeably there are some examples where processed speech can appear clearer and yet be no easier to understand

(Carmichael, 2004) so the distinction is an important one. The relationship between the two factors would be expected to be close in most cases however using the descriptor ‘speech clarity’ could be expected to be more influenced by other factors such as the more ambiguous ‘quality’ than the more objective, score based measure of

could be expected to be similar however there are circumstances where this may not be the case. A completely isolated speech channel would undoubtedly produce better intelligibility ratings but the complete absence of music and sound effects important to scene comprehension may produce poorer ratings for enjoyment for some AV media with some participants.

In designing subjective assessments for audio conditions it is critical to understand the nature of the data or information required that will allow the most useful analysis. For this thesis the use of quantitative methods combined, where appropriate, with objective measurement of conditions has been used. This approach has however been informed by informal semi-structured interviews with participants in the research. The outcomes of the interviews have not been used to derive clear research conclusions but instead have been used to gain some insight into why particular results may have been obtained and to inform the development of test methods used during the research.

Zielinski’s review of biases in audio listening quality tests identifies much of the potential for gaining meaningless or misleading data from listening tests (Zielinski et al., 2008) and all of this is relevant in the design of tests during the research presented here. The biases identified include recency effects, listener expectations and

preferences, stimulus related biases such as uneven frequency of presentation, scale and range related biases and biases resulting from the appearance of the experimental interface.

The nature of research involving hearing impaired participants mitigates against the adoption of standard test methodologies used for audio assessment and also creates substantial challenges for the researcher. When discussing listening tests for

loudspeaker assessment Toole (1985) identified a number of what he called ‘nuisance variables’ that could cause large variability in subjective assessments, these were split into those associated with the listening environment, those related to the listeners themselves and those related to experimental procedure or test design and are presented

here in order to assess the ‘nuisance variables’ that can and can not be excluded from the research documented in this thesis.

Toole’s ‘Nuisance Variables’

Listening environment factors: • Listening room • Loudspeaker position

• Relative loudness (of compared sounds) • Absolute loudness (of all sounds) • Program material

• Electronic imperfections

• Stereo (peculiar technical problems) Listener factors:

• Knowledge of the products • Familiarity with the programme • Familiarity with the room • Familiarity with the task • Judgement ability or aptitude

• Hearing ability (physical impairment) • Relevant accumulated experience • Listener interaction and group pressure • Stereo (conflicts between spatial and sound quality aspects of reproduction)

Experimental Procedure:

• Identification of perceptual dimensions • Scaling of the perceptual dimensions • Anchoring or normalisation of individual scales

• Effects of context and contract • Effects of sequence and memory • Experimenter bias

(Toole, 1985)

Clearly there are considerable challenges for the researcher in assessing audio reproduction conditions using subjective test methodologies. Listening tests

documented in international standards have the advantage that where the potential for biases exist, they are well understood and can therefore be mitigated against to a large degree. For subjective assessment of audio systems with hearing impaired participants there is considerably more potential for unpredicted biases to appear and great care must be taken in developing test methodologies for this group. Perhaps unsurprisingly most research into improving TV sound for hearing impaired people has focused largely on signal processing methods and carefully controlled subjective assessments with hearing impaired participants have been rare. This thesis aims to fill some of these gaps and develop robust test methods for assessments of potential answers to the problems that hearing impaired people experience in viewing TV in their homes.