Spectral Correlates of Timbral Semantics Relating to the Pipe Organ
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Dept. for Speech, Music and Hearing Quarterly Progress and Status Report Spectral correlates of timbral semantics relating to the pipe organ Disley, A. C. and Howard, D. M. journal: TMH-QPSR volume: 46 number: 1 year: 2004 pages: 025-040 http://www.speech.kth.se/qpsr TMH-QPSR, KTH, Vol. 46, 2004 Spectral correlates of timbral semantics relating to the pipe organ Alastair C Disley & David M Howard University of York, Department of Electronics, Heslington, York YO10 5DD, UK ABSTRACT This paper explores whether words used to describe pipe organ ensembles have correlation with specific spectral features. Similar previous work has concentrated on single pipes in anechoic conditions (e.g. Rioux, 2001). This work examines pipe organ ensembles as a cohesive whole. Ninety -nine English-speaking subjects were asked to describe recordings of pipe organs. From the many timbral adjectives they used, seven words were chosen that were useful, unambiguous and frequently used. In two experiments, guided by previous studies of timbral adjectives in other timbre spaces, the spectral correlates and common understanding of these words was examined. All five words that exhibited common understanding had spectral correlates that to some degree supported theories suggested by previous research. The earlier part of this work was presented in Disley & Hpward (2003). This research has since been developed and refined, with particular emphasis on careful selection of adjectives for study and detailed consideration of steady-state spectral correlates. Most clearly defined existing theories of spectral correlation appear to hold true in this complex timbre space. This paper was presented at the Joint Baltic -Nordic Acoustics Meeting (BNAM 2004) in Mariehamn, Åland, June 8-10, 2004. 1. Introduction stops with a sub-octave component. Readers unfamiliar with the terminology or tonal Previous research in the field of timbral synthesis of the pipe organ are referred to semantics (e.g. Rioux, 2001; Nykänen & Owen & Williams, 1988, and Anderson, 1969. Johansson, 2003) has concentrated upon single Helmholtz pitch notation is used throughout sound sources such as individual organ pipes this paper. recorded in anechoic conditions. This paper takes that research into the real world situation of multiple source ensembles in natural 2. Summary of previous acoustic environments, and aims to develop a research library of potential spectral analyses suitable The authors’ initial research in this area was for this new context. These analyses are then published in Disley & Howard (2003) and is used to examine the results of previous summarized in this section along with previous research by the authors described in Disley & relevant research on timbral adjectives and Howard (2003) , looking for correlation with information on a novel visual analysis used in adjectives that have proved to have common Disley & Howard (2003). understanding in this context. Pipe organs have been used as a tool for 2.1 Experimental procedure experimental use as they provide controllable and repeatable samples in a manner unique The aim of this research was to establish among large multi-source ensembles. This whether any timbral adjectives commonly used research concentrates on the principal chorus in the context of a pipe organ ensemble had of the pipe organ, excluding reed, flute and demonstrable common understanding. Fifty string stops. The principal chorus for this English-speaking subjects were asked to research is defined as all stops of the principal describe the sound of four different pipe family on the primary keyboard of the organ, organs’ principal choruses. Ninety-nine including mixture stops but excluding any adjectives were extracted from their answers, Speech, Music and Hearing, KTH, Stockholm, Sweden 25 TMH-QPSR, KTH, Vol. 46: 25-40, 2004 Disley AC & Howard DM: Spectral correlates of timbral semantics ..... and seven were selected for further study based Those samples were recorded from five on common occurrence and a lack of obvious different pipe organs, with one organ having potential confusion in this context. Those recordings made both with and without its words were "balanced", "bright", "clear", mixture stop. The organs recorded were all in "flutey", "full", "thin" and "warm". the United Kingdom: Although these words had not been studied 1. Doncaster Parish Church (Schulze, 1862, in the context of pipe organ ensembles, some German romantic style organ) previous research suggested theories of 2. Heslington Parish Church, York (Forster spectral correlation that could be relevant here. and Andrews, 1888, mixture added 1974) "Bright" is correlated to both spectral centroid 3. St Chad’s Parish Church, York (George and spectral width in von Bismarck (1974), Benson, 1891, mixture has 17th component) Dodge & Jerse (1985), Campbell (1994) and 4. Port Sunlight URC, Merseyside (Willis, Risset & Wessel (1999). These two theories 1904) are difficult to isolate as all conventionally useful pipe organ ensembles have some 5. Jack Lyons Concert Hall, York (Grant, fundamental frequency component and thus Degens and Bradbeer, 1969, neo-classical any increase in spectral centroid will be highly style) correlated with an increase in spectral width. All samples were recorded from a typical "Clear" could be related to a decreased listener position, as each organ is voiced for its number of harmonics and spectral slope room. A recording made very near the pipes (Ethington & Punch, 1994), the strength of the will have different timbral qualities to one second harmonic (Jeans, 1961) or an increase made in the room (Syrový et al., 2003) and in spectral centroid (Solomon, 1959). "Thin" hence its sound will not be representative of has been related to a lack of lower frequency the sound desired by the organ’s builder. spectral components (Hall, 1991). "Warm" has been associated in Risset & Matthews (1969), 2.2 Initial results and theories Pierce (1983) and Rossing (1990) with small Initial analysis of results was based upon the degrees of harmonic inharmonicity, but this is acoustic signatures of each ensemble. As the inconsistent with the harmonic synthesis of a steady-state spectrum of an organ is essentially pipe organ chorus, as any such variation would harmonic, the acoustic signature plots the result in the separate pipes ceasing to blend amplitude of each harmonic against a third into one coherent ensemble, adding to dimension of keyboard range, so that it is perceived roughness. "Warm" is also possible to view the changes in spectrum correlated with a lower spectral centroid and between low and high notes. Each of the an increase in energy of the first three ensembles had ten samples taken across the harmonics in Ethington & Punch (1994), and keyboard range (each C and F-sharp) which this is supported in Pratt & Doak (1976) along were then analyzed using a Fast Fourier with decreased spectral slope. Transform (4096 point Hamming window) and Those seven words were used as rating a custom Matlab script to generate harmonic scales in two comparative experiments that strength information. The acoustic signatures aimed both to explore the degree of common for each ensemble are presented in Figs 1 to 6. understanding present and to begin the search Common understanding was demonstrated for spectral correlation. The two most popular for the words "flutey", "warm" and "thin". The words, bright and clear, which both had a good less rigorous tests for "bright" and "clear" also number of theoretical spectral correlates, were indicated that some common understanding used in a large-scale listening test with 75 was present. "Full" and "balanced" did not untrained listeners. The remaining words were demonstrate common understanding in this used in a smaller-scale listening test with 22 context, and were excluded from further study. volunteers, all of whom had previous pipe The simple theories developed from organ listenin g or playing experience. Both observation of the acoustic signatures are tests used four samples drawn from a pool of presented in Disley & Howard (2003), but a six, with the specialized test exhaustively more precise means of identifying correlation comparing all samples but the unspecialized between test subjects’ ratings and particular test comparing two specific pairs. spectral features was desired. 26 TMH-QPSR, KTH, Vol. 46, 2004 St. Chad's 842 60 50 50-60 40-50 40 30-40 20-30 C 30 10-20 F# 0-10 c Amplitude (dB) 20 f# c1 10 f#1 Pitch c2 0 f#2 0 2 4 6 8 c3 10 12 14 16 18 20 22 f#3 24 Harmonics 26 28 30 32 Figure 1. Acoustic signature for the St Chad’s ensemble (without mixture). St. Chad's 842M 60 50 50-60 40-50 40 30-40 20-30 C 30 10-20 F# 0-10 c Amplitude (dB) 20 f# c1 10 f#1 Pitch c2 0 f#2 0 2 4 6 8 c3 10 12 14 16 18 20 22 f#3 24 Harmonics 26 28 30 32 Figure 2. Acoustic signature for the St Chad’s ensemble with mixture. Speech, Music and Hearing, KTH, Stockholm, Sweden 27 TMH-QPSR, KTH, Vol. 46: 25-40, 2004 Disley AC & Howard DM: Spectral correlates of timbral semantics ..... Doncaster 884T2C 60 50 50-60 40-50 40 30-40 20-30 C 30 10-20 F# 0-10 c Amplitude (dB) 20 f# c1 10 f#1 Pitch c2 0 f#2 0 2 4 6 8 c3 10 12 14 16 18 20 22 f#3 24 Harmonics 26 28 30 32 Figure 3. Acoustic signature for the Doncaster Parish Church ensemble. Jack Lyons 842M 60 50 50-60 40-50 40 30-40 20-30 C 30 10-20 F# 0-10 c Amplitude (dB) 20 f# c1 10 f#1 Pitch c2 0 f#2 0 2 4 6 8 c3 10 12 14 16 18 20 22 f#3 24 Harmonics 26 28 30 Figure 4.