AquaSynth/docs/research/auditory-notifications

Auditory Notification Research Distillation

This ledger grounds AquaSynth Dings in auditory-interface research without pretending that a desktop agent notification is a medical or aviation safety alarm. The local PDFs are research inputs, not redistributed product assets.

Findings that constrain the implementation

• Use decaying, percussive envelopes. Foley et al. found temporally varying, percussive tones less annoying and more detectable than flat tones under concurrent speech load. Every curated instrument therefore has a short attack, brief sustain, and decaying tail. Flat beeps and broadband noise are rejected.
• Map urgency through timing deliberately. Haas and Casali compared 0, 150, and 300 ms inter-pulse intervals; shorter intervals increased perceived urgency without improving detection time. Routine AquaSynth motifs therefore keep onset gaps in the 180–320 ms range. We do not make ordinary progress notifications sound urgent merely to make them noticeable.
• Keep pitch and spectral agitation restrained. Hellier, Edworthy, and Dennis found speed, fundamental frequency, repetition, and inharmonicity all affect perceived urgency. The catalog stays in a calm mid register, uses consonant C-major intervals, limits brightness, and forbids noisy timbres.
• Do not rely on arbitrary melodies alone. Sanderson, Wee, and Lacherez found poor learning and persistent confusion in a standardized melodic alarm set. Here the motif grammar is small and systematic: landing pitch and motion carry event class, while timbre independently identifies the speaking agent.
• Expect masking when sounds overlap. Bolton et al. experimentally showed that masking a tonal alarm's primary harmonic can make it indistinguishable. The service mixes concurrent sounds, but the curated catalog intentionally separates timbre families and exposes stop_dings; a later field test should measure identification under realistic overlap before expanding the catalog.
• Prefer a small, tested vocabulary. Studies of IEC melodic alarms and overlapping alarms show that nominal distinctness is not reliable human discriminability. New instruments require listening/identification trials; parameter validation is only admission hygiene.

Implemented policy

• Event selects motif; instrument selects agent identity.
• Instrument source is catalog-only. MCP callers cannot inject patch scripts.
• Root frequency: 196–392 Hz.
• Brightness curation score: 0.20–0.78.
• Decay: 0.25–1.50 seconds; attacks remain short and nonzero where practical.
• No broadband-noise instruments.
• Multi-note onset gaps: 180–320 ms.
• One persistent playback mixer owns the output device.
• Aqua daemon remains the sole synthesis authority.

Sources

1. Foley, L. et al. (2022), More detectable, less annoying: Temporal variation in amplitude envelope and spectral content improves auditory interface efficacy, JASA 151(5), DOI 10.1121/10.0010447. Saved as foley-et-al-2022-more-detectable-less-annoying.pdf.
2. Hellier, E. J., Edworthy, J., & Dennis, I. (1993), Improving auditory warning design: quantifying and predicting the effects of different warning parameters on perceived urgency, Human Factors 35(4), DOI 10.1177/001872089303500408.
3. Haas, E. C., & Casali, J. G. (1993), The Perceived Urgency and Detection Time of Multi-Tone and Frequency-Modulated Warning Signals, HFES Annual Meeting, DOI 10.1177/154193129303700906.
4. Sanderson, P. M., Wee, A., & Lacherez, P. (2006), Learnability and discriminability of melodic medical equipment alarms, Anaesthesia 61(2), DOI 10.1111/j.1365-2044.2005.04502.x.
5. Lacherez, P., Seah, E. L., & Sanderson, P. M. (2007), Overlapping Melodic Alarms Are Almost Indiscriminable, Human Factors 49(4), DOI 10.1518/001872007X215719.
6. Bolton, M. L. et al. (2020), An Experimental Validation of Masking in IEC 60601-1-8:2006-Compliant Alarm Sounds, Human Factors 62(6), DOI 10.1177/0018720819862911.
7. NIST Technical Note 1950, Auditory Warning Signals. Saved as nist-tn-1950-auditory-warning-signals.pdf.

The source README for the event vocabulary is https://github.com/iain/minimal-dings/blob/main/minimal-dings/README.md.