boettche@cat27.CS.WISC.EDU (Michael Boettcher) (02/17/89)
I am looking for a device or some way of allowing me to use my modem, and
talk to the person on the other end of the line.
I was thinking that if there isn't a source of such a device at a reasonable
(for a college student) price, that it souldn't be too dificult to make
something like this.
If the output of a microphone/amp were put into a IC that compresses the
frequency band down to a few hundred hertz (assume 3000 hz band to begin
with) it could be placed on top of the band that the modem is using. If
the person at the other end of the line had something to decompress the data
and send it to a speaker, the people on both ends of the line could talk.
There are a few things that would need to be done, such as filtering the
signal for each (modem and speech circuit). My main question is if the
voice signal can be compressed by a factor of ten, and if there is enough
room at the top (or bottom) of the band sendable by the phone lines to
place the compressed signal. I have heard that the phones only have a
3000hz bandwidth.
Anybody have any information that would help?
Thanks in advance.
Michael Boettcher Student, University of Wisconsin, Madison
boettche@garfield.cs.wisc.eduPloni.Almoni@mailcom.FIDONET.ORG (Ploni Almoni) (02/19/89)
Michael -- you are on the right track but are going sideways!! What you want already exists, but the way it is done is to leave the audio signal as is and to carry the DATA channel in a narrow bandwidth either just outside the normal audio bandwidth (above or below) or to superimpose the data channel in a "hole" chopped into the audio spectrum. The first method is done on certain types of AM broadcast transmitters to telemeter transmitter data or control things like electric meter switching, and the second method is most common in telephony. The data rate is usually 300 baud although the same technique could be used for higher rates. HOWEVER - this is not a "home electronics" do-it-yourself project, and the modems involved cannot be found on the pages of Computer Shopper! They are not cheap, in other words. Hope that helps somewhat to dispel the fog. -=Ploni=- -- Via apple!mailcom, Fido 1:204/444