Relative pitch representations and invariance to timbre

Abstract

Information in speech and music is often conveyed through changes in fundamental frequency (f0), the perceptual correlate of which is known as "pitch". One challenge of extracting this information is that such sounds can also vary in their spectral content due to the filtering imposed by a vocal tract or instrument body. Pitch is envisioned as invariant to spectral shape, potentially providing a solution to this challenge, but the extent and nature of this invariance remain poorly understood. We examined the extent to which human pitch judgments are invariant to spectral differences between natural sounds. Listeners performed up/down and interval discrimination tasks with spoken vowels, instrument notes, or synthetic tones, synthesized to be either harmonic or inharmonic (lacking a well-defined f0). Listeners were worse at discriminating pitch across different vowel and instrument sounds compared to when vowels/instruments were the same, being biased by differences in the spectral centroids of the sounds being compared. However, there was no interaction between this effect and that of inharmonicity. In addition, this bias decreased when sounds were separated by short delays. This finding suggests that the representation of a sound's pitch is itself unbiased, but that pitch comparisons between sounds are influenced by changes in timbre, the effect of which weakens over time. Pitch representations thus appears to be relatively invariant to spectral shape. But relative pitch judgments are not, even when spectral shape variation is naturalistic, and when such judgments are based on representations of the f0.

A unitary model of auditory frequency change perception

“…Local frequency changes in SFS may then be more informative for harmonic sounds, whereas coarser SE cues may take over for inharmonic changes. However, a recent study tested pitch discrimination with interference of envelope variation and did not observe a mediating role of harmonicity in all conditions [26]. Instead, they only found a mediating role for very large intervals (9 st) or in the case when there was no overlap between the frequency components of the two sounds, but not for natural speech or musical instrument sounds.…”

“…Speculatively, it can be remarked that harmonicity plays an important role in auditory scene analysis [65][66][67]. In particular, harmonicity favors the binding of frequency components within and across sounds [26,65]. Local frequency changes in SFS may then be more informative for harmonic sounds, whereas coarser SE cues may take over for inharmonic changes.…”

“…For inharmonic sounds, recent results by McPherson and McDermott add yet additional candidate cues to try and explain pitch judgements [25]. Using a variety of tasks usually understood as involving pitch, such as pitch discrimination, melodic contour identification, or interval judgments, the authors concluded that pitch judgements were in fact based on multiple mechanisms operating concurrently, such as the computation of f 0 from SFS cues for harmonic sounds, and the tracking of SE cues for inharmonic and harmonic sounds (see also [26]). Previously, frequency-shift detectors tracking local changes in SFS cues had also been evidenced [27], providing yet another mechanism contributing to “up” or “down” pitch judgements available for harmonic and inharmonic sounds alike [28].…”

A unitary model of auditory frequency change perception

“…Speculatively, it can be remarked that harmonicity plays an important role in auditory scene analysis [ 70 – 72 ]. In particular, harmonicity favors the binding of frequency components within and across sounds [ 29 , 70 ]. Local frequency changes in SFS may then be more informative for harmonic sounds, whereas coarser SE cues may take over for inharmonic changes.…”

“…For inharmonic sounds, recent results by McPherson and McDermott add yet additional candidate cues to try and explain pitch judgements [ 28 ]. Using a variety of tasks usually understood as involving pitch, such as pitch discrimination, melodic contour identification, or interval judgments, the authors concluded that pitch judgements were in fact based on multiple mechanisms operating concurrently, such as the computation of f 0 from SFS cues for harmonic sounds, and the tracking of SE cues for inharmonic and harmonic sounds (see also [ 29 ]). Previously, frequency-shift detectors tracking local changes in SFS cues had also been evidenced [ 30 ], providing yet another mechanism contributing to “up” or “down” pitch judgements available for harmonic and inharmonic sounds alike [ 31 ].…”