asterisk users - Aug 2005 - how can I reduce delays in meetme with zap channels

My boss is complaining that the delay between speaking and hearing in a 
meetme conference is noticeable and doesn't want to roll out our system 
until I can eliminate the delay.

Personally, I don't think the delay is significant, but I don't sign his
check.

The system consist of 3 1u's, each with a single quad t1 card. Each card 
has 2 t1's running NFAS.

The "t1 hosts" dial the "conference host" using IAX.

All of the hosts are in the same rack connected by 1000 Mbps full duplex.

My "scientific" method of measuring the delay is to call in on 2
phones. I
listen with one phone while I tap the handset of the other phone against 
the table. Does anybody know how to objectively quantify the delay?

Does anybody know of any reference material that says "delays less than x 
ms is undetectable to humans :)

Would changing from IAX to SIP help? I've heard that SIP may be better as 
the number of connections rise.

Would TDMoE be better?

Would any settings in iax.conf or zapxxx.conf help?

Thanks in advance,
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Steve Edwards      sedwards@sedwards.com      Voice: +1-760-468-3867 PST
Newline           pagesteve@sedwards.com            Fax: +1-760-731-3000