When comparing iRig Pro Duo vs Saramonic Smartrig+, the Slant community recommends Saramonic Smartrig+ for most people. In the question“What are the best cord/splitter/ DAC / portable headphone amp/ portable sound mixer (that can fit in a pocket) to record two or more microphones and listen/monitor live?” Saramonic Smartrig+ is ranked 1st while iRig Pro Duo is ranked 2nd. The most important reason people chose Saramonic Smartrig+ is:
Some microphones require this to work. It's good that this preamp can provide that if needed.
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Pros
Pro Works with popular OS'
Works with iOS, Android, Mac and Windows PC
Pro Can run on batteries for portable use in a pinch
Pro Can provide 48v phantom power
Some microphones require this to work. It's good that this preamp can provide that if needed.
Pro Can choose mono or stereo recording for inputs
Mono keeps inputs separate giving versatility in post, stereo mixes inputs them together removing ability to alter inputs separately.
Pro Has 2x XLR combo jacks + 2x 3.5 mm input jacks
The XLR Combo jacks allow for 2x XLR jacks such as for professional grade equipment, 1/4" inputs such as for guitars, and two 3.5mm TRS inputs, such as for lapel microphones or consumer/prosumer grade equipment.
Pro Has headphone monitoring jack / output
Besides the built in TRRS output cable, there is a 3.5 mm jack for monitoring, but it could be considered a 2nd output jack using a male to male cord.
Cons
Con Must use wall charger to power iPad
Con Battery life is about an hour
Better batteries can be bought to extend play/record time but not by much.