Re: Feeding audio signals into phone lines

[ddl@danlan.*com (Dan Lanciani)]

In article <f7r8m5$ius$1@xxxxxxxxxxxxxxxx>, Bill@xxxxxxxxxxxxxxxxx (Bill Geluso) writes:

| Anyway, my question is:  What is the simplest (and least expensive)
| way to feed an audio signal into a telephone line?
|
| My specific application is as follows:  My speech is next to
| impossible to understand due to cerebral palsy.  Therefore, I often
| use a speech synthesizer to communicate with people, including
| people over the phone.  Currently, to "speak" over the phone, I
| depend on the microphone in a conference phone to pick-up the sound
| waves coming from the speaker in my speech synthesizer.  While this
| configuration works, the quality of the sound that gets transmitted
| over the phone line is less than satisfactory.  This is why I am
| seeking a direct way to input an audio signal into a phone line.
|
| When making suggestions on how to accomplish what I want, please
| keep in mind that I don't use a Windows computer with a sound card.
| I still use a DOS computer, mostly because I can't/don't like using
| a mouse.

Ignoring the legality of connecting directly to the phone line, likely
the best way (in the sense of highest quality audio) to accomplish this
is with a 600 Ohm 1:1 audio isolation transformer (possibly still available
at Radio Shack).  Connect one side of the transformer in series with an
0.1uF capacitor to the phone line.  Drive the other side of the transformer
with the speaker output of a small audio power amplifier.  (A 1W unit suitable
for "bookshelf" speakers is fine.  You don't need a lot of power, but often
you do need more than is available from a line output.  Having the volume
control and possibly some tone adjustment is useful too.)  Connect the output
of your speech synthesizer to a line input of the amplifier.

I've tried a number of commercial couplers over the years and none come
close in quality to the above approach.

				Dan Lanciani
				ddl@danlan.*com