Hi,
You schematic says 4v peak to peak, which is 2v peak which means the positive peak is +2v and the negative peak is -2v, unless it is offset with a dc voltage too. If it is offset then you might need a coupling capacitor.
The coupling capacitor should be a value large enough to pass the lowest frequency of operation, but because it looks like you're using a buffer you may find that it works better with some resistance from the buffer input to ground also. You might get away with 1megohom, but you may have to use 100k for lower noise.