A Second-Order Cepstral Signature of Contact-Vibration Sounds Reproduced by Laptop Loudspeakers: A Synthetic Case Study
2026-06-03 • Sound
SoundMultimedia
AI summaryⓘ
The authors studied why the sound of a phone vibrating on a hard surface through laptop speakers sounds different from regular recordings. They found that special repeating patterns, called nested periodicities, exist in the vibration's sound at both a basic and a more detailed level. By simulating the entire process from vibration to speaker playback, they showed that some of these patterns remain or become clearer at certain stages, especially at the phone and laptop speaker. However, the authors emphasize that their model is a first step and needs real-world testing with actual recordings and listener feedback.
cepstrumnested periodicityvibrationmechanical generationsignal chainsound propagationencoding/decodinglaptop speakersaudio playbackcontact vibration
Authors
Jim Salsman
Abstract
A mobile phone vibrating on a hard surface often sounds qualitatively unlike ordinary audiovisual recordings when reproduced through laptop loudspeakers. We propose that part of this perceptual distinctiveness can be described as a nested periodicity: a first-order cepstral structure reflecting the vibration period and its multiples, and a second-order cepstral structure reflecting repeated spacing within the first-order cepstrum. Treating the perceptual effect as real and using a deliberately transparent synthetic signal chain, we model six stages: mechanical generation, surface and air propagation, microphone capture, encoding and decoding, laptop-speaker playback, and re-recording or post-processing. The synthetic analysis shows that the first-order cepstral periodicity is preserved across the chain, whereas a cleaner bimodal or quasi-bimodal second-order cepstral signature is most evident at the mechanical source and at laptop-speaker playback. The result supports, but does not prove, the hypothesis that laptop reproduction can re-emphasize a latent contact-vibration periodicity that is less cleanly expressed in intermediate recorded and encoded forms. We frame second-order cepstral bimodality as an exploratory descriptor of contact-vibration playback rather than as a completed perceptual metric. Required validation includes recordings of real devices, controlled playback transfer functions, perceptual judgments, and comparisons against ordinary speech, music, and environmental recordings.