One vacil equals a 60 dB 1 kHz tone fully amplitude-modulated at 4 Hz

Evidence

Because fluctuation strength is a sensation which one considers separately from other sensations, both absolute and relative values are useful. A fixed point is therefore defined for a 60-dB, I-kHz tone 100% amplitudemodulated at 4Hz, as producing 1 vacil (from vacilare in Latin, or vacillate in English). — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1382 (#expands, via linked claim)

Categorization

• XREF: connects to: One acum is defined by a 1 kHz narrow-band noise at 60 dB.; The vacil unit anchors fluctuation strength to a 4 Hz modulated tone — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1382; The ear is most sensitive to amplitude modulation near 4 Hz (+1 more)

Broader Connections

• The vacil unit anchors fluctuation strength to a 4 Hz modulated tone #expands (0.95) — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1382
• The ear is most sensitive to amplitude modulation near 4 Hz #responds-to (0.75)
• Pitch strength of amplitude-modulated tones depends critically on the carrier-to-modulation frequency ratio #qualifies (0.70)