Assertion: tone | /r/HasAspect | modulation
Facets:
value: at 90 hz
type: TEMPORAL
Source sentences:
text: The Precise Tone Plan for the North American Numbering Plan of the US, Canada, and various Caribbean nations specifies a combination of two tones (350 Hz and 440 Hz) which, when mixed, appear to have a modulation at 90 Hz.