A few thoughts for the ones interested by using the (not perfect) embedded ADC and DAC controllers 
:
The ADC controller is a cyclic pipeline 12-bit 1 msps ADC with differential input mode and programmable gain stage (datasheet page 1318). As stated in the article of reply # 1, this ADC controller is not a perfect one, however a technique to correct for some errors is to calibrate with an appropriate method. Offset and gain error parameters of this ADC can be improved by calibration, this Atmel Application Note gives all details:
http://www.atmel.com/Images/doc11106.pdf
In free running mode, the maximum of 1 msps gives some room to operate calibration and averaging. The MLA assembler instruction (Multiply with Accumulate, 32-bit result, 2 clock cycles) is well suited for that purpose.
On the other side, the DAC controller is well known to output a voltage between 1/63.3 and 5/63.3. However there is a remedy for this and with a gain G = 1.5, the output of this circuit has the desired range from 0 to 3.3V:
https://create.arduino.cc/projecthub/ArduPic/how-to-modify-analog-output-range-of-arduino-due-6edfb5?f=1
BTW for those interested by a bipolar analog I/O with a DUE, you might be interested by this:
http://ardupiclab.blogspot.fr/2015/10/