Fluctuation strength is standardized against a 4 Hz amplitude-modulated reference tone

Evidence

The unit of fluctuation strength is the vacil, where the reference point is selected by prescribing that a 1-kHz sinusoid at a level of 60 dB with 100% amplitude modulation at 4 Hz produces a fluctuation strength of magnitude 1 vacil. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1219

Categorization

• DEFINE: Defines the vacil, the measurement unit for fluctuation strength.