Dumb beginners question about measuring impedance

[mayfin]

I've been reading the section in the documentation about using REW to measure impedance. It talks about the soundcard output and in particular recommends using the headphone out rather than line out ... but what about the input ?

Should the input used be Mic In, or Line In ?

And if you have a soundcard with line in/line out, what would be the recommended value of Rsense ?

(I'd love to be able to work this out from first principles, and not waste everyone's time asking what seems to be an easy question, but I don't know enough to know where to start ...)

 

[John Mulcahy]

Use line in. Here's the relevant part of the help:

Good results can be obtained using a headphone output (or, even better, a good headphone amplifier or a device with a high power headphone output) to drive the load, with a 100 ohm sense resistor. If a line output is used the sense resistor typically needs to be larger as line outputs have high output impedance and limited drive capability, try 1 kohm but note that the results will have much higher noise levels and be more susceptible to background noise. If the device being used to drive the load can cope with lower loads a lower sense resistor, 47 ohm for example, will improve the results.

 

[mayfin]

Use line in. Here's the relevant part of the help:

Good results can be obtained using a headphone output (or, even better, a good headphone amplifier or a device with a high power headphone output) to drive the load, with a 100 ohm sense resistor. If a line output is used the sense resistor typically needs to be larger as line outputs have high output impedance and limited drive capability, try 1 kohm but note that the results will have much higher noise levels and be more susceptible to background noise. If the device being used to drive the load can cope with lower loads a lower sense resistor, 47 ohm for example, will improve the results.

Thanks - much appreciated.

I'd seen and read the section about using line out, and how this affected the value of Rsense, but didn't know if this was in turn affected by the choice of input port.