How to measure a the output impedance of a DAC? Well, impedance is not the same in all frequencies, we say impedance, not resistance, because impedance depends on frequency.
Well, suppose we do the meassures with 1khz. You generate one khz with the dac at the out put, and without load you measures 1V, for example. Then you put a resistance of for example 1kohm, and now you read 800mv.
Now we apply Ohm. V=I.R, I=V/R, so I=0,8/1000, I=0,0008A, 0,8mA
R=V/I, So Zout=(1-0,8)/0,0008= 250ohm
And one thing, 22kohm is higher impedance than 100ohms. Better 100ohm than 22kohm, of course.
Well, suppose we do the meassures with 1khz. You generate one khz with the dac at the out put, and without load you measures 1V, for example. Then you put a resistance of for example 1kohm, and now you read 800mv.
Now we apply Ohm. V=I.R, I=V/R, so I=0,8/1000, I=0,0008A, 0,8mA
R=V/I, So Zout=(1-0,8)/0,0008= 250ohm
And one thing, 22kohm is higher impedance than 100ohms. Better 100ohm than 22kohm, of course.
The output impedance is not 22k. The output impedance is what you 'see' looking into the output. What you see is 22k in parallel to the output impedance of the DAC (assuming the cap is too large to matter).
You can easily measure it. First play a steady tone like 1000Hz and measure the output voltage. Then add a load resistor of say 1k to the DAC output, again play the tone and again measure the output level.
With the extra load the level will be lower. How much? Well that depends on the output impedance. I think you can see that when the output impedance would be the same as the 1k load, then the extra 1k load should drop the level to half.
There is a simple equation for this: 1K/(1k + output impedance) = level with 1k load / level with no load.
Edit: I see ManoloMos already said something similar ...
Jan
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For a better answer we need to know what is the specific problem you have to solve.
As a side note, the "High Pass Filter" shown cutoff frequency varies a lot depending on the load driven after it.
It's difficult to answer without a schematic.I supposed the output is buffered after the actual DAC so the most relevant parameter will be the output OPAMP's impedance.You could find it in the datasheet.If there are other filters/components after it they will contribute too.
Best approach is to use an active buffer as suggested.To make one pick an opamp with good enough parameters(since we talk about audio and it's a buffer hence G=1 any modern cheap OPAMP should be ok as long Gain-Bandwith product is above 500Khz-1Mhz and you get more than 4-5 V/us slew rate.Pick one with some drive capability.NJM4556 would fit the bill.)
You tie the Inverting input to the output and feed the signal to the Non inverting one.Basic opamp buffer.