🚀 go-pugleaf

I'm building my own secure voice telephony (digital speech scrambler ) and I
would like to use it over the telephone. I've some questions for any of you
Telcom or DSP type people or anybody that's done this before.

1.) My design right now incorporates a 14 bit serial output ADC. I sample the
speech at 7khz which is double the bandwidth of telcom speech. The output from
the ADC is XOR'ed with a 31 stage linear feedback shift register that generates
several hours of pseudorandom "noise" before it repeats itself. (It's clocked
at 7khz to give me that long turn-around time.) This encrypted data stream gets
sent over the telco line (in theory) and the receiving party whose PN generator
is synced with mine, decodes the encrypted data stream and the remaining voice
bits are routed to his/her DAC. My question is 7khz too fast for telcom ?
I've heard of speeds of 9600 baud with modems. Appreciate any help with this.

2.) The quick and dirty way I've synced the pseudonoise generators of the
calling and receiving parties is that I've 2 LM567 tone decoders that monitor
the telco line for say...the digit 7 (852hz + 1209hz.) When it detects that
tone, the 567's both send a low out to a NOR gate 74LS02 which sends out a high 
which enables the 74LS164 shift registers that create the pseudonoise.
The high from the 74LS02 also gets routed through an inverter which then goes
to a low which enables the chip select lines on the ADC's and DAC's.

Ideally, both calling and receiving parties will detect the #7 digit at the
same time and therefore be synced up. I haven't built up this part of the
circuit yet, but it looks good on paper. Any of you guru types see any problems
with this please let me know.

3.) I've heard of all this talk about 1 bit ADC's DAC's, Sigma Delta
converters, Pulse code modulation. Are these converters more appropriate for my
design ? Do I still have to sample at twice the bandwidth with these converters
to get understandable speech or, are they 1:1 linear type converters ? What is
meant by pulse code modulation ?

4.) I'm more of an analog Pulsed power type of guy, but I'm having a lot of fun
trying to prototype this scrambler. I'll appreciate any help and ideas from
anybody that could save me some time. Thanks.

Guy
Urbina@novax.llnl.gov