Why start_delay=1 for capture and start_delay=0 for playback

what this means

I have one app which does both capture and playback, but when i tried to read ALSA buffer(capture) periodically it gives ALSa buffer overflow error. what my app does is read from ALSA (capture mic) and write to ALSA(playback).

In this case for both Capture and Playback setting i am using start_delay = 0.

But if i am giving some delay between Read and Write no overflow error happens

Any idea why this happens

Thanks