A simulation of a :00.5 second duration time tone as heard every hour over the NBC radio and television networks.  This is no simple 'sine' tone; the main 750 Hz duration (as averaged; hourly tones ranged from 688 Hz to 804 Hz over the years) was augmented by lower-volume harmonics at 1500, 2250, 3000, 3750, 4500 and 5250 Hz (and probably also 6000 Hz), thus almost resembling a cross between a triangle and a sawtooth wave.  Used of varying durations (anywhere from :00.3 to :00.7 seconds) from at least the 1950's into the '80's.

Simulated NBC Hourly 'Beep' Time Tone

Re-creations of the two versions of CBS's "chirps" as part of their NetAlert cue tone system.  The first is from the time the system was first put into use in 1961, the second is from after its update / upgrade in 1978.  As in keeping with the network's policy, the frequencies and durations are kept under wraps.  Just enjoy this stroll down memory lane.

CBS Radio 'NetAlert' Chirps - Simulations of 1961 and 1978 Versions

A simulation of the 16 different 'chirps' of the late 1970's (Mk III) version of CBS Radio's "NetAlert" system.  A 'priming' tone (2241 Hz, the first and fifth tone heard in each sequence), plus any of four other tones (1845, 2100, 2391 and 2722 Hz) were used in different combinations of five total tones, in rapid succession, the sequence on this file as follows:

0 - Reset
1 - Start Network Feed
2 - Local Cutaway
3 - Rejoin Network
4 - End Network Feed
5 - Spare
6 - Spare
7 - Closed Circuit
8 - Speed Feed
9 - Bulletin
10 - Exclusive Bulletin
11 - Special Report
12 - Update Report
13 - Spare
14 - Very Special Report
15 - National Emergency

1 through 4 would have been the most heard, mainly within the hourly CBS Radio newscasts.  15 is what most likely would have been activated on the morning of Sept. 11, 2001, when the World Trade Center in lower Manhattan was attacked and, summarily, brought down.

This replaced the system that was first enacted in 1961-62, with two tones repeated for every function (i.e. 3 times for closed circuit transmission, 9 times for a national emergency).  In turn, this system lasted up to 2009.

Wmbrown6

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