🚀 go-pugleaf

Can voice be transmitted over RS-232 lines?  The answer is yes, and it is,
but you must be more specific.  If you want to speak in a microphone, into
a computer, and have speech sent serially there are many ways to do it, but
it is fairly complex.  Data rates of understandable speech can vary from
9600 baud to 300 baud by using different methods.  I'll tell about these
below.  

If you don't want real-time vocoding, you just want to transmit data
representing speech, you can send the ASCII characters down the line, and
then have one of radio-shacks text-to-speech chips on the other computer,
to convert to speech.  Alternately, you can break the words you want to
send into phonetic pieces, and send codes for these pieces down the line,
at an even lower rate than the ASCII spellings of the words.  Toys such
as Speak & Spell store phonetic data like this in ROMS.  Parts cost is
around $20, if you already have the computers to transmit serial data.

If you want to run real-time vocoding, (speak into microphone, have computer
process it, and send it over serial lines.) there are many ways to do it.
You can use LPC vocoding, which is in common use in the military.  GTE
makes several miltary vocoders to do this at baud rates around 9600, or 4600
baud, but it sounds bad at these lower rates.  I think 9600 baud is about
the worse you can deal with.  You can code this LPC algorithm on a DSP
microprocessor for around $100 in parts.  Look in the library under
LPC coding of Speech.

MIT Lincoln Laboratory recently developed an algorithm called "sinusoidal
coding of speech."  It sounds much better at lower baud rates.  It makes
LPC coding sound terrible in comparison.  4800 bps data rates sound very
natural.  I can give you many references on this (call or email.) 

BBN recently developed a very low rate vocoding algorith, called the
"LPC Segment Vocoder"  that was recently (what time is it?) implemented
in real-time by MIT Lincoln Laboratory.  This codes speech at 300 bps,
and sounds fairly understandable.  It relies on tremendous lookup tables
of several megabytes, and requires lots of hardware.  I can also give
many references on this algorithm (call or email.)

DISCLAIMER:  I am no expert in this area, but worked for several people 
experts for a period of time.  All information is from the top of my head,
and could be wrong.  My employer doesn't necessary share in any of my
opinions.

			- Thomas E. Jones
			tj@xn.ll.mit.edu
			(617) 981-5093 (work)

-- 
tj@xn.ll.mit.edu or tj@ll-xn.arpa          (one of these should work)
Thomas E. Jones, home (617) 279-0767 work (617) 981-5093