(2017) and effects unfolded analogously to the original pitch experiments. The general design of the experiments followed the approach described by Chambers et al. In this letter, I have described two experiments that examined timbral brightness shift judgments for tone pairs with fixed pitch, using stimuli with a harmonic spectral fine structure and cyclic spectral envelope components. In analogy with Chambers et al., this ambiguity was expected to resolve with the presentation of context tones in experiment 2. Given that the present stimuli shared the cyclic nature of the classic Shepard tones, the same ambiguity effects known from pitch were expected for half-octave shifts in experiment 1. Specifically, upward spectral shifts were presumed to yield brighter sounds. would unfold for brightness judgements in both experiments. Following the reported commonalities between pitch and timbral brightness perception, I hypothesized that analogous effects compared to Chambers et al. Experiment 2 tested the extent to which responses for the most ambiguous shifts were modulated by prior context. Experiment 1 established a relation between the magnitude of the spectral shift and listeners' perception of brightness change. Instead of using Shepard tones or random spectra, the fundamental frequency was held constant and stimuli were varied in terms of the spectral envelopes. The experiments described in the following are modelled according to the first two experiments by Chambers et al. However, to my knowledge, no reports of systematic ambiguity or context sensitivity of timbral brightness perception exist that would parallel the described effects for pitch. At the same time, a recent neuroimaging study suggested no systematic anatomical distinction between the cortical regions that subserve the encoding of pitch or brightness variation ( Allen et al., 2016). Russo and Thompson, 2005 Melara and Marks, 1990). They observed symmetric mutual interference of pitch and brightness in a discrimination task, when differences in sensitivity between attributes and participants were controlled (cf. Allen and Oxenham (2014) studied interactions between auditory attributes. (2013) found strong commonalities between pitch and brightness processing for sequences of varying length, but distinct patterns of results for loudness. Also testing auditory sequence discrimination, Cousineau et al. (2008) showed that listeners recognized transposed timbral brightness (and loudness) patterns in similar ways compared to pitch patterns, which indicates that relative representations, commonly thought of as a hallmark feature of pitch, could be a general feature of the auditory system. Some of these were sourced from acoustic recordings, like the fans and motors.Although timbral brightness and pitch are usually studied in separation, core commonalities have been registered. The bubbles recording is a good example of that. A few are quirky attempts at discovering what variety of sounds could be used and still keep the illusion intact. Many in this collection are synthesized and intended to be used as a layer within an additional bed of sound. These inspired me to do some experimenting with creating some Shepard tones for myself. I was made aware of the effect years ago in school but was reintroduced to it a few years ago when Randy Tom used it in the movie “Flight” to add tension to a particularly long crashing descent.Īnd more recently, it was used in Dunkirk by the composer Hans Zimmer. The Shepard tone effect has been used in many films over the years. This can create a sense of tension since the tone never seems to resolve. A Shepard tone is an aural illusion where the pitch of the sounds appears to be ever increasing.
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