MikeMI,
Thank You, the DC in the input is unkonwn, depend on the DC offset of other equipment, can be anything but maybe the max is a few mV, so 6.3V cap is OK?
Nigel Goodwin,
Thank You, the goal is to achieve as small as possible phase shift in the 10Hz, and the bipolar I have in hand max 1000uF, seems good enough, just not sure the cap voltage needed, from MikeM answer above, the voltage rating needed should be higher than DC in the signal, I think most of the audio device should not have more than few mV DC so 6.3V is OK, am I right?