-=> Quoting Arthur Marsh to Mark Griffiths <=-

 AM> On Sat 14 Dec at 15:09 Mark Griffiths (3:640/305) wrote to Arthur
 AM> Marsh: 
 MG> Have you heard of equalization?  Equalizers allow you to go 
 MG> beyond the 3dB cutoff points by modifying the transfer 
 MG> function of the channel so that the equalized channel 
 MG> has a more linear performance.  The high frequency 
 MG> response of a phone line is limited by the low pass 
 MG> filters before and after digitization.

 AM> Yes, and the signal-to-total distortion ratio plummets if you
 AM> over-equalise. 

Of course, over-equalisation is no better than not using equalisation at 
all.

 AM> The V.34 probe tones of 3450 Hz and 3600 Hz some-how 
 AM> have to figure out the high frequency roll-off of such 
 AM> a connection...
 
 MG> According to Telstra, I'm on an S-12 exchange, and I almost 
 MG> invariably get 3429 symbol rates on my connections using a Courier.

 AM> What data signalling rates?

The main modems that I call are:-
V.34 only (Netcomm) modems on digital lines - 28.8k connects
V.34+ (Netcomm) modems on the same digital lines - 31.2k connects 
(SNR = 36.5dB)
Jabberwocky (Courier V.Everything) 33.6k connects (50% of the time 
speedshift up from an initial 31.2k connect)

What do you reckon on these 56k protocols?  I reckon they are going to have
some pretty shocking Inter-Symbol Interference with symbol rates at 8000/sec
on lines with only 3500Hz bandwidth...

Regards,
Mark Griffiths.

... They can have my modem...when they pry it from my cold dead fingers.
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