Ever heard a dial tone? By the human ear it is 90 HZ. Curious. When first implemented it was done using twisted wire pairs. Frequency response was optimized as 3kHz Flat and then C-message weighting (response curves optimized for certain frequencies). The bottom end of the response curves were usually kneed below 300Hz or so.
Just how did, does a subscriber hear that 90 Hz so loudly?
[Answer] The human ear responds to the lowest product of combinations of frequencies. It is essentially a biological equivalent of a diode mixer. It ‘hears’ the lowest intermodulation product of two frequencies: 250 Hz and 340 Hz.....amazing, huh?
I remember that. I was in HS at that time, and we were one of the first areas, iirc, to be upgraded to an ESS.
Gone went the 5-digit local dialing and we had to use all seven digits after that.
The new switch also offered new features that you could pay for, too, such as 3-way calling/conferencing/call waiting.
” In some metropolitan areas, particularly New York City, individual
message registers per line were provided for charging purposes.
Generally the register was scored once for each call. As the dialing
distances increased, complex district selector and junctor circuits
were developed for the panel and No. 1 crossbar systems that permitted
the multiple scoring of registers on the answering of the call, as
well as additional scorings at the beginning of each overtime period.
[also known as message units, bulk billing or measured service].”
This brings back memories of customers disputing message units and the pen register tests.It was a pain in the butt.
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“That IS interesting isn’t it...”-
Actor James Woods’s character’s reply to Angela Bassett’s character when she said to him, “What IS interesting is that it recorded exactly 18 hours of it.” from the 1997 movie “Contact”.