Can someone help me with this schematic?

I found this schematic for an amplified listener from www.Biotele.com and I'm having trouble finding c4 in this circuit, a 5n cap.  I'm wondering what its purpose is and what range of values could i use to replace it?

Picture of Can someone help me with this schematic?
Its needed to roll off the HF response of the circuit, I don't think its that critical.
Re-design7 years ago
You can use two cap in parellel they just add up. Like a 2 and a 3 = 5. 
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Or caps in series work like this link.