I made the same point you just did concerning RTOS. I was told Real Time is a piece of cake on PC's or Macs. These comments are earlier in this thread.
Now we can not have it both ways. Someone here is wrong....
It is,depending on your definition or "real time" what kind of cake and the size of the piece of cake.
"pretty fast" and "almost instantly" "barely noticable" and "negligible delay" don't count as "real time".
THe easiest test to perform is this: I stumbled on it accidentally when each kid turned on the TVs really loud so I could hear both "at the same time".
Two different model satellite TV receivers tuned to the same tv program, create an echo when you listen. One of the two lags behind just enough to create the echo effect.
I expect with a "conventional radio and a SDR tuned to the same station side by side, the SDR will have a noticable delay varying depending on the model/type of SDR.
I also know that any number of "conventional" radios tuned to the same station have no audible delay
As for music production, USB microphones for example, include a 3.5mm jack for monitoring in "real time" before the signal enters the digital chain.
has one and this one actually mentions the delay /latency issue : http://www.musiciansfriend.com/pro-audio/blue-yeti-usb-microphone
...The Yeti utilizes a high quality analog-to-digital converter to send incredible audio fidelity directly into your computer, a built-in headphone amplifier for zero-latency monitoring, and simple controls for headphone volume, ...
I call all this phenomenon "asychnronous real time". Of course when you have two realities that are out of step with each other, although they make pills for that for humans, they don't have a pill of radios yet