[mdlug] It happened...

[Aaron Kulkis]

Joseph C. Bender wrote:
> Michael Rudas wrote:
>> I'm not sure how that would work, considering that it IS a dual-tone
>> system and would require two simultaneous, precise tones to work --
>> one each corresponding to the column and row of the keypad.  It takes
>> a LOT more than perfect pitch to do that -- even Captain Crunch (Jon
>> Draper) needed a two-note bosun's whistle to pull off a similar stunt.
>>
> 	I've seen it sort-of done.  Effectively you hum and whistle at the same 
> time.  The tones don't have to be that precise, you should see the 
> tolerances on your average 1980's DTMF decoder IC for how much the input 
> tones are allowed to wander +/- the base frequency for each tone.  1.5 
> to 3 percent isn't unusual on a modern decoder, even.

Primarily because there isn't much need to be, as long
as proper separation of tones is achieved, and normal
conversation isn't interpreted as DTMF, then the tolerance
is "good enough."