Found this little snippet:-

Almost identical to mine except mine runs at 2KHz...

Index 1372 - Circuit Diagram - SeekIC.com

Back to your reply:-
In the above cct the C 0.1uF in that case is acting as a DC blocker exactly the same as mine.
Mine has 100K to ground on the input and 1M to ground on the output, there is a reason, - why?

The TC, (time constant), on the O/P when not connected to anything at all is 1 Second.
This approximately gives me a turnover real audio frequency of 1Hz at 6dBV down. The upper limit depends on CCT strays. This TC is OTT for a 2 KHz chopper clock signal but I tend to go OTT at times.
I could have used 0.01uF and this would still work because the TC is 100Hz before turnover occurs.
The C is purely for AC coupling and is technically in fact a high pass filter not low pass.
High-pass filter - Wikipedia, the free encyclopedia
Low-pass filter - Wikipedia, the free encyclopedia

I want the 2 KHz to go through as it is AM at any random DC, in other words it is effectively a carrier of 2 KHz modulated at any random DC level.
It goes without saying that with a little jiggery pokery an AC signal modulating this carrier could be used to extend the BW of the MBPs microphone audio from DC - 20KHz fairly flat.

It works and if you want real AC coupled oscilloscope displays then I will create some when the box is finished.

And finally the WHOLE system is AC coupled so I don't really need the 1uF and 1M at all.
But this is modular project which leads to what I was taught......
NEVER put DC into any random black box system without some kind of blocking capacitor and in my case a 1M shunt resistor.

EDIT:
A simple CCT change that generates a 2KHz carrier at 1V P-P, where a maximum of 2V P-P signal, centred at 1V instead of ground, can modulate it from DC to say 200Hz.

Code:

                               R3 = 1M
    O/P O-----------------*----/\/\/\----+ 
                          |            __|__
                          |            /////
                         === C1 = 1uF
                          |
 LF AC OR    R1 = 1K      |
 DC I/P O----/\/\/\----*--*--+
                       |     |
                       \     o C  Q1 = BC549
                       /      \    b
             R2 = 100K \       \|__o----/\/\/\----O Square wave in from approx 2KHz multivib.
                       /       /|      R4 = 22K
                       \     |/_
                       /     o e
                       |     |
   _GND_  O----*-------)-----*--------------------O
             __|__     |
             /////     |
                       |
  +1V REF O------------+