Looking to buy a decent quality earphone for my regular as well as gym needs. Comparing them, I found that some had this feature while others didn't. What does it mean? From the little I could find online was in sense of aural signals viz, mono means one channel, stereo means spatial and dual stereo means two channel. "Does it mean I can play audio file in one ear phone and attend a call in other. Or does it mean that two audio signals from my phone/device will play but superimpose?"