Hello. I’m new to this forum and I’m hoping someone can help me out. I’m looking for a way to create simulated CBET/eCBET tones for use in some AM and FM radio effects I’ve made. It’s a controversial encoding technology for retrieving listener data that adds a pretty unique ‘metallic’ or ‘buzzsaw’ sound to radio broadcasts.
From the Signal Identification Wiki:
CBET/eCBET tones are a set of 10 frequency modulated tones between 1-3kHz. These signals are inserted into broadcast audio in over 50 major markets for identification by “Portable People Meters” used in Nielsen’s rating scheme. Nielsen controversially purports that these signals are encoded in such a way that they are ‘masked’ by the program audio.
There are 10 bands, each of which can carry 1 of 18 tones. There are 16 tones to a signal, so the stream is 4 bits wide, and the other two tones are used as “STOP” and “SYNC” markers. This allows for an data rate of 8 bits per second to be encoded onto the audio. All bands carry identical information, but each bit within a band is encoded with a different tone from any of the other bands. This appears random or uncorrelated at first glance, but the pattern emerges pretty quickly if you do a long enough analysis. The same message gets identically repeated 12 to 13 times per minute and the message only changes once per minute.
It doesn’t have to be perfect, just as long as it sounds fairly close.
Here’s an audio sample of the tones (from Signal Identification Wiki):