source file: mills2.txt Date: Thu, 5 Oct 1995 12:58:04 -0700 From: "John H. Chalmers" From: mclaren Subject: Tuning & psychoacoustics - post 12 of 25 --- The psychoacoustic evidence for the periodicity and Fourier-analysis-based models of hearing has now been examined. But what about interaction between these two ear/brain systems? Evidence for this comes from David Wessel's examination of a psychoacoustic effect known as "streaming" in the mid-70s: "Consider a melodic line of eleven tones where the even-numbered tones and the odd-numbered tones are separated in register. As shown...at a rate of 5 or 6 tones per second, a listener would hear the sequence as a coherent succession. At a faster tempo--10 to 12 tones per second--the high tones group together to form a separate stream from the low tones. At an odge, C., Jerse, T. "Computer Music: Synthesis, Composition and Performance," 1985, pg. 47] Time is a crucial factor in pitch perception, implying further feedback between the periodicity and Fourier-analysis systems of pitch detection: "The data...show that the just-noticeable relative frequency difference increases with decreasing test-tone duration. (...) At long durations (around 500 ms) a critical-band rate difference of 0.01 Bark represents the just- noticeable difference for pitch. At a duration of 10 ms, the JNDF amounts on average to 0.2 Bark. For a decrease of the test-tone duration by a factor of 10 ms, the magnitude of the JNDF, expressed in critical-band rate, increases by a factor of 10. Thus pitch differences which are easily detected at logn durations are no longer distinguishable at short durations. This effect is well known to musicians: inaccuracies in intonation, easily detected in sustained tones, almost disappear if the tones are considerably shortened in duration, for example by playing `spiccato.'" [Zwicker, W. and H. Fastl, Psychoacoustics: Facts and Models, 1990, pg. 116] Other results make it clear that the perception of pitch is dependent on the temporal order of tones: "When presented witha group of spectral components, a listener may or may not fuse them into the percept of a single sound. One of the determining factors is the "onset asynchrony" of the spectrum which refers to the difference in entrance times among the components. (...) Rudolf Rasch has noticed a related phenomenon with regard to the synchronization of tones in chords in polyphonic music. He has found that the amount of asynchrony in starting times of chord tones actually improves our ability to perceive the individual tones while we continue to perceive the chord as a whole. Rasch has shown that the effect obtains best when the attacks of the tones are spread out over a time span of 30 to 50 msec." [Dodge, C., and Jerse., T. "Computer Music: Synthesis, Composition and Performance," 1985, pg. 59] Because of this unexpected interdependence of time with freqeuncy perception, it seems likely that all 3 of the ear's mechanisms for processing sound interact to some degree. There is further evidence for this interaction between all 3 ear/brain systems in the form of auditory paradoxes: "Paradoxical effects can be obtained thanks to the precision and flexibility inherent in computer synthesis. Shepard produced a sequence of 12 tones in chromatic succession which seem to rise indefinitely in pitch when they are repeated. I extended this paradox and generated, e.g., ever-ascending or descending glissandi, and sounds going down the scale and at the same time getting shriller. These paradoxes are not merely "truquages"--artificial curiosities: they reflect the structure of our pitch judgments. Pitch appears to comprise a focalized aspect, related to pitch class, and a distributed ascpect, related with spectrum, hence with timbre--and the paradoxes are obtained by controlling independently the physical counterpart of these attributes, which are normally correlated. I have even manufactrured a sound which does down in pitch for most listeners when its frequencies are doubled--i.e., when one doubles the speed of the tape recorder on which it is played; this shows how misleading mere intuition can be in predicting the effect of simple transformations on unusual sounds." [Risset, J.C., "The development of Digital Techniques: A Turning Point for Electronic Music?" Rapports IRCAM No. 9, 1978, pg. 7] These effects make clear the importance of context and the subtlety of interaction among the ear's various methods of sound processing. This would tend to militate against tuning theories which stress absolutes like beats or the convenience of easy modulation, and would support instead the use of non-just non-equal-tempered tunings whose context-driven character mirrors this aspect of the ear/brain system. --mclaren Received: from eartha.mills.edu [144.91.3.20] by vbv40.ezh.nl with SMTP-OpenVMS via TCP/IP; Fri, 6 Oct 1995 07:40 +0100 Received: from by eartha.mills.edu via SMTP (940816.SGI.8.6.9/930416.SGI) for id WAA01139; Thu, 5 Oct 1995 22:40:25 -0700 Date: Thu, 5 Oct 1995 22:40:25 -0700 Message-Id: <951006053855_71670.2576_HHB33-5@CompuServe.COM> Errors-To: madole@ella.mills.edu Reply-To: tuning@eartha.mills.edu Originator: tuning@eartha.mills.edu Sender: tuning@eartha.mills.edu