What is the longest gap time between the cancelation and restoration of a harmonic that will create the perception of a single sound source as opposed to two?
Griffin Leonard
Canceled Harmonics Threshold:
The first 10 harmonics of a 200 Hz fundamental frequency is presented, followed by several cancelations and restorations of the 3rd harmonic. The time between each cancelation and restoration is decreased after a brief period of silence. This should separate into two different sound sources, one that sounds like a constant tone and that sounds like beeping. By decreasing the gap between the cancelation and restoration of the 3rd harmonic, I hypothesize that eventually the sound sources will merge together and sound like a single tone interrupted by brief "glitches". If this is the case, what is shortest gap that creates the perception that there are two separate sound sources?
Citation:
Darwin, C. J., & Sutherland, N. S. (1984). Grouping Frequency Components of Vowels: When is a Harmonic not a Harmonic? The Quarterly Journal of Experimental Psychology Section A, 36(2), 193-208. https://doi.org/10.1080/14640748408402155
Comments
Griffin Leonard
c) The subjective reports answer the question, and indicate that the sound sources merge into one around the 5th clip, where the gaps in the 3rd harmonic are 1/64th of a second.
d) This experiment demonstrates a threshold when the 3rd harmonic is missing, but would this threshold change if a higher frequency harmonic was removed? Would the threshold change if a different fundamental frequency was used? Would changing the length of time that the harmonic is presented as opposed to changing the length of the gap change this experiment? All of these questions could be addressed with small changes to the experiment.
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Emily Huang
a) I heard a "glitchy" lower tone and a higher beeping tone until the fifth clip, at which I heard only the glitchy tone and not the harmonic anymore.
b) I think this demo does a good job of answering the question of how large the gap between the cancellation and restoration of the harmonic can be before we hear a single tone, although I'm not sure if the glitchy effect is a confounding variable. I'm not sure how you'd regulate that, since the glitch is from, I presume, the third harmonic being gone.
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Griffin Leonard
@Emily Huang,
the glitchiness you describe is probably from the removal of the harmonic itself, I don't know how I would be able to remove that. Thank you, this is good feedback.
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Jeremy Ma
a) Before the 5th sound clip, I was able to clearly hear a quiet beep, and a louder constant tone, although the larger tone was not really constant, it was kind of glitchy, which made the illusion slightly confusing. Around the 5th/6th sound clip, I was only able to hear one glitched tone.
b) I think this demo was able measured the detection threshold of the idea of continuity in harmonics, I would assume perceptual filling occurs when the gap is sufficiently small which is why we perceive one tone after clip 5. However the glitches of the main tone does seem to mask this gap, so I am unclear if the gap was being masked by the glitches, or did perceptual filling occur.
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Griffin Leonard
@Jeremy Ma,
I don't think there was any perceptual filling. The 3rd harmonic blends into the rest of the harmonics as a single sound source when the gap is decreased enough. Thank you for the feedback!
