Are you sure the sound he is hearing is not the modem fan screeching? :P > -----Original Message----- > From: Pete Resnick [mailto:presnick@QUALCOMM.COM] > Sent: Tuesday, June 11, 2002 1:37 PM > To: Lloyd Wood > Cc: Bill Cunningham; ietf > Subject: Re: modems > > > On 6/11/02 at 9:04 PM +0100, Lloyd Wood wrote: > > >You're confusing your modems and your acoustic couplers. > > > >An electrical transmission in the ~3.5kHz bandpass range that equates > >to the dominant frequencies used by the human voice, which the phone > >system was engineered to convert and carry easily, is not a sound. > >Modulating an electrical signal into said electrical > transmission does > >not involve sound. > > OK, OK, of course that's exactly correct; almost all modems today > completely bypass the issue of sound and transmit directly through > the copper to the telephone switch. But let's get back to the > question Bill was asking and why he was asking it: > > > On 6/11/02 at 3:22 AM -0400, Bill Cunningham wrote: > > > > >I know modems communicate on the physical layer by > electrical pulses > > >or binaries sent on copper wires. > > The important feature of modems is that they send analog signals over > those lines, not digital (which is what I took Bill to mean by > "binaries"). And those analog signals correspond quite directly to > things that create sound (if connected to a speaker of the right > sort) and receive sound (if taken from a microphone of the right > sort). It is the correspondence to the receiving and production of > sound that makes modems interesting devices; that's why acoustic > couplers worked on the old modems. Similarly touch tones are *tones* > because they can pass through a system designed for transmitting > analog electrical signals that can be turned into a sound. (Hence, > you could go out and by those touch-tone producing boxes, program > phone numbers into them, hold them up to your phone receiver, and get > the number dialed.) > > Yes, it is correct that most modems today deal with electrical > transmission only and not sounds (except for their speakers). But it > is the fact that those signals can easily become sounds that is key, > at least to explain to Bill why his modem is screeching. (Although > some of my friends in philosophy of science disagree, "explanation" > is not a matter of reducing everything to physics.) > > It's times like this I think the IETF needs more academics. :-) > -- > Pete Resnick <mailto:presnick@qualcomm.com> > QUALCOMM Incorporated - Direct phone: (858)651-4478, Fax: > (858)651-1102 > >