[BC] dtmf tone filter solutions

[Kirk Harnack]

ABC, NBC, CBS, and Mutual radio networks all used audible signalling
over leased lines and satellite. Concurrent digital signalling was and
stilll is used on satellite.

Mutual had the famous "bee-doop" signals. CBS's sounded like dropping
Alka Seltzer tablets into water. NBC's were pleasant, though I don't
know the format. ABC's were rather high-pitched.  All were at low
level - often below the gating threshold of station audio processors.

I really don't think any were deemed illegal.

Indeed, DTMF tone filters are really delays with muting, activated by
incoming DTMF tones.

Kirk



On 9/17/08, RichardBJohnson at comcast.net <RichardBJohnson at comcast.net> wrote:
 > ...and the 110 volt ringing frequency is?
 >
 > http://telecom.tbi.net/phone.htm
 >
Of course sub-audible signals pass over phone lines. It's done all 
the while. It may be that some scum-sucking accountant that took over 
some broadcast operation got away with punching holes in program
material to use DTMF, but it doesn't mean that one is supposed to use 
it that way.

In fact, when I was in Radio, CBS was sued because they used some 
audible high-frequency squitter to signal over the network. Since it 
was within the normal program audio band, the FCC disallowed its use 
and CBS had to replace their queuing boxes with ones that used 
sub-audible tones.