Semiología y espacio El sentido del espacio

Rock ‘n’ roll ain’t gonna die…”

From AC/DC’s ‘Back in Black’ Album

While Rock ‘n’ Roll isn’t going to die, nor is noise. The problem, to date, has been in describing what “we” mean by noise. Noise is not just “loudness”, nor just “unwanted sound”, whatever they may be. Noise has character, and as such can be described in terms appropriate to its prominence in an individual’s perception. The methods of measurement in acoustics ‘describe’ sound pressure and energy but, as is canvassed in this work, these descriptions are inadequate for the task of characterizing the nature of human perception. Acoustical measures are limited in their application to noise with various measures of magnitude and energy being of assistance to the task. Sound quality measures provide a link or shift to human perception and to acoustical measures. Sound quality incorporates both qualitative and quantitative measures. Music, however, has a rich set of descriptors that are ideally suited to describing noise in qualitative and quantitative measures. It does not, however, have the same measures available that are well documented for acoustical analysis of a sound.

Intrusive sound can be objectively characterised as being quiet or loud (having amplitude or loudness), it usually has some form of irritating tone (tonality) and possibly a beat of some sort (modulation in frequency and amplitude). It may be persistent (long duration) or intermittent (short duration) or it could be impulsive. The sound may startle (having a short attack time) or suddenly stop (fast decay). It can be repetitious or infrequent. The important distinguishing feature, however, is that it ‘stands-out’ in its environment; that is, it can be regarded as being atypical of the ‘normal’ environment. Intrusive sound must, therefore, be measured and assessed with respect to its environment. This is usually inside the home. Standard ‘noise’ investigations do not readily fit into this measurement and assessment scenario – primarily because there are few measurement and assessment methodologies to accommodate the scenario. Noise is a subset of intrusive sound; that is, noise must have some additional characteristic that makes it irritating or annoying. The psychophysical relationship to noise is to ‘establish firm relations between the

physical magnitudes of sounds and the correlated perceptual magnitudes’ (Fastl, 2002). This relationship has been explored by Fastl (2000); Green (1970); Stevens (1970); Torgerson (1970); Zeitler & Hellbrueck (1999). These works describe the analysis loudness, sound quality and pleasantness of sounds, and directly link to the perception of sounds.

The measurement and assessment of low amplitude intrusive sound requires a selection from all three groups of acoustical, sound quality and musical descriptors. Sound, apart from individual perception, can be described in terms of its aural texture, as shown in Table 4.3.1:

Table 4.3.1: Measures of aural texture

Acoustical measures Musical measures

sound level loudness

spectrum complexity pitch

presence of pure tones or narrow frequency bands within a broad-band spectrum (tonality)

tonalness

fluctuation or modulation effects in either, or both, amplitude and frequency, sharpness and roughness

Timbre, described in terms of dissonance

impulsive characteristics attack and decay

duration duration

The difference between the two formats is that the first, the acoustical measures, have no ‘humanness’, they are simply measures, like a ruler or a measuring flask. The second set of descriptors has human feeling as well as definable measure (Genuit, 2002). A combination of both provides a toolbox of measures and methods that can describe any sound, and most importantly, measure low amplitude sound. The acoustical terms dealing with sound level, tonality and duration are well defined in International Standards such as ISO 1996-1 and ISO 1996-2. Spectrum complexity is not well defined, but it is reasonable to bring loudness in at this stage. Modulation is

another effect that is not well described in acoustics, although the effects are well known (van den Berg, 2006). In the second set only loudness has some definition, and this is for stationary signals. Tonality is a vital issue and guidance is still open to debate (Bienvenue, 1986; Hastings and Davies, 2002; Hoare Lea Acoustics, 2004). Impulsiveness is described in the various measures reported by Hoare Lea Acoustics (2004).

The second set of descriptors is far better represented. Loudness has a large support- base from, for example: Chalupper (2000) and dynamic loudness; Chouard (1998) loudness and pleasantness; Florentine, Namba and Kuwano (1986) loudness, noisiness and annoyance; Fridrich (2002) Zwicker stationary loudness; Hellbrück (1991) loudness scaling; Hellman and Zwicker (1987a, 1987b, 1989) loudness measures; Hiramatsu, Takagi and Yamamoto (1988) rating loudness, noisiness and annoyance; Kuwano and Namba (1985) overall and instantaneous loudness; Kuwano, Fastl and Namba (1999) loudness, annoyance and unpleasantness; Moore, Glasberg and Baer (1997) loudness; Persson, Bjorkman and Rylander (1990) loudness in low frequency sounds; Pollack (1970) loudness and transportation; Suzuki and Stone (1993) frequency characteristics of loudness.

Noise can be described as ‘ugly acoustics’ (Höge, 1986) or sound that is ‘aesthetically unpleasant’. Pleasantness is a classic definition for ambience in, for example: Bengtsson, Waye and Kjellberg (2003); Zeitler and Hellbrueck (1999). If one takes unpleasantness as an attribute for noise then the effects of changes of pitch and tonality become significant, with dissonance, consonance, roughness and timbre all valid descriptors. Bolger and Griffith (2003); Daniel and Weber (1993); Helmholtz (1954), Parncutt (1989); Sethares (2005); Terhardt (2000); Terhardt, Stoll and Seewann (1982a, 1982b) all present different but similar approaches to the complex issue of ‘tonalness’ in all its forms. Parncutt (1989) describes sounds variously in terms of, for example, chroma, chroma salience, complex sound, complex tonalness, equivalent frequency, harmony, melody, pitch, pitch difference thresholds, pitch prominence, threshold of pitch, tones and tone sensations. Terhardt (2000) describes pitch perception with spectral and virtual pitch, sensory consonance and auditory roughness. Helmholtz (1954) describes cents, semitones, sensory consonance and sensory dissonance. This is a very small sample of a rich language compared to the

paucity of description in ISO 1996-1 where only 6 major categories for sound levels are described. Admittedly the Standard does have other assessment methods but they are variations on the ‘sound level’ or amplitude theme.