In 2375, The Doctor sang up to a range of 880 hertz in order to check for damage to Chakotay's auditory nerves. This was done after exposure to chaotic space had reactivated a previously suppressed gene that caused, among other symptoms, auditory hallucinations. (VOY: "The Fight")
The frequency in the message transmitted by V'Ger was sent at a rate of one million megahertz and lasted only a millisecond. At that high rate of speed, the message was initially undetected. (Star Trek: The Motion Picture)
1 million megahertz is actually equal to 1 terahertz.