Harmonic fusion and pitch affinity: Is there a direct link?

Area of Science:

• Psychoacoustics
• Auditory Perception
• Signal Processing

Background:

• Simultaneous pure tones approximately one octave apart often fuse perceptually into a single pitch.
• Successively presented pure tones exhibit pitch affinity when their frequency ratio is near one octave.

Purpose of the Study:

• To investigate the relationship between perceptual fusion of simultaneous tones and pitch affinity of successive tones.
• To determine if these two auditory phenomena are directly related.

Main Methods:

• Stimuli consisted of triplets of pure tones with frequency ratios between 0.96 and 1.04 octaves.
• Tones were presented simultaneously or successively at a low sensation level (15 dB) in broadband noise.
• Eighteen listeners performed extensive stimulus comparisons.

Main Results:

• Maximal fusion for simultaneous tones occurred at a frequency ratio deviating less than 0.2% from one octave.
• Maximal pitch affinity for successive tones occurred at a frequency ratio slightly larger than one octave.
• Fusion decreased less rapidly above the optimal ratio than below it, while pitch affinity decreased more rapidly above its optimal ratio.

Conclusions:

• The distinct optimal frequency ratios and differing decrease rates suggest harmonic fusion and pitch affinity are unrelated perceptual phenomena.
• Auditory processing of simultaneous and successive tones differs significantly around the octave interval.