The best tools for the job are as follows IMO:
Smaart
SysTune
PRAXIS
They have further advantages over stand-alone units and other basic RTA PC programs in that they have FAR more features and have more than one "channel" for comparative analysis (great for comparing pre & post processing effects/response). I am sure there are more out there, but the above choices are among the best.
Also, I believe all of them have free demo/trial downloads as well.