Study of the Perceptual and Semantic Divergence of Digital Audio Processed by Restoration Algorithms

This research integrates sensory and scientific instruments to analyze the relationship between subjective evaluations of digitally restored audio and its computer extracted perceptual descriptors. Statistical methods have been used to compare the displacement of three types of remediated content in subspaces obtained by data expressed both by individuals and by feature extraction algorithms. Qualitative demands in audio restoration are tightly connected to the information embedded in remediated content: it is crucial the awareness that every choice is re-balancing it and affecting its reception. Listeners in their turn don’t do an acousmatic reduction of auditory information but recode it interleaving contextual and aesthetic approaches, according to their sensitivity and being influenced by their cultural background. Thanks to the analysis of the displacement in subspaces related to the descriptive characteristics with greater variability, the semantic divergence resulting from the operations of improving the quality of sound was interpreted and a predictive model aimed at their optimization was assumed. 1. RESTORATION BETWEEN ARCHIVE, CONSERVATION AND REMEDIATION The practice of audio restoration grounds on a solid methodological basis derived mostly from cultural heritage maintenance. Audio restoration concerns firstly the production of a conservative digitized copy and the implicated technical and cultural issues. In this view its object is the overall audio content, which embodies several layers of information about the mediated content, the acoustic context, the techniques of the recording and the history of the carrier where the audio is stored in. Guidelines on how to handle the digitization procedure are issued mostly from archive science [1, 2] and should be as neutral as possible in respect to its intrinsic complexity. The digitization of degraded or degradable audio documents is surrounded by a whole set of opportunities related to dissemination, once the digitized medium becomes the subject of conservation of cultural heritage. In this context Copyright: c ©2014 Sonia Cenceschi et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 3.0 Unported License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. the study of the complexity of information regressively influence the strategy of restoration, leading to categories of approach like documental, recovery, sociological, and aesthetic, which scruple to lose the information which are respectively considered as ancillary [3, 4, 5, 6]. The practices of audio restoration have been finally considered in the view of the theory of mediation [7]. Referring to the concept of remediation as the representation of one medium in another [8], restoration techniques may be conceived as the key to unleash the potential of audio as a medium, in a frameworkwhere the conservation of cultural heritage has to face with increasing functional demands 1 . 1.1 Re-evaluating the Aesthetic Content Despite maintaining substantial theoretical similarities with restoration in general, the role of auditory perception, coupled with the substitution of a tangible object with the digitized copy, makes audio restoration very prone to subjective assessments: if on the one hand restoration aims at recovering and enhancing the medium by acting on certain features, on the other hand this does not necessarily imply optimal improvements in terms of psychology of auditory perception. Different restoration approaches fear not only the loss of information, but even the mismatch between purposes and aesthetic judgement. This is implicit in the use of restoration algorithms in order to emphasize the qualities of the medium, which have the collateral effect of projecting it in a listening dimension which is divorced from history. From the point of view of audio restoration, one may argue that the applying of techniques should anyway take care of aesthetic considerations 2 . Rather, the categories of modern audio restoration may benefit from the correlation of computational analyses of the audio medium both from an object-oriented and a listener-centered approach. The need to determine aesthetic appreciation preventing this to remain an issue of hermeneutics led audio restoration being finally addressed with object-oriented methods of systematic musicology which tries to explain musical 1 It should be pointed out that a rigid division between a truly archival perspective and several functional, or even commercial approaches in audio restoration is somehow unrealistic: the common practice admits the intervention on local as well as global flaws as later described, albeit in different proportions, and every approach benefits from the same research results in digital signal processing. Recent developments in the creation of conservative copies through optical digitization [9, 10, 11], once regularly implemented, may help revealing goals and needs of the different individuals and groups making decision rules. 2 This question should not be confused, whether the specialized restorer may be an artist besides a technical expert or a scientist, which is not a debate among scholars and practitioners. A. Georgaki and G. Kouroupetroglou (Eds.), Proceedings ICMC|SMC|2014, 14-20 September 2014, Athens, Greece