Why is it ok to use polarized caps to remove DC offset from an audio input?
As long as the DC level is positive, the AC amplitude of the audio signal is of no consequence because it is a "coupling" capacitor, in the sense that the RC time constant is much higher than the highest 1/f of the audio signal (excluding dc of course), so the capacitor never gets "charged up" to the audio ac signal voltage (only to its dc value).  Instead, the voltage across its terminals remains approximately constant. In other words, the capacitor rides with the input, and if the RC constant was not high enough, audio would be distorted.  For example, you could have 1V of dc offset and 10V of ac amplitude.  If RC is high enough, the voltage accross the capacitor will ALWAYS be very near 1V,NOT 11V to -9V as the comment to the first answer seemed to imply.  Hope this helps.