Is it possible to achieve longer delay times (around 500ms) by adding external RAM through I2C?
Unfortunately this is not possible with the 1701 -- please see http://ez.analog.com/message/8940#8940
This feature will be available for the ADAU1452, see http://ez.analog.com/message/138108#138108
although this chip includes no internal audio ADCs and DACs.
If your delayed signal only needs limited frequency response (such as voice quality), there's a few tricks that allow you to trade bandwidth for delay time. Both of these sound better to me than they have a right to:
Twice the delay at 10KHz bandwidth: http://ez.analog.com/message/74499#74499
Four times the delay at 5KHz bandwidth: http://ez.analog.com/message/8940#8940
Retrieving data ...