capacitor or resistos to isolated mixed sources?

capacitor or resistor to isolate mixed sources?

Hi, when I as young, our teacher show us a passive mixer, each entrance had only one green capacitor in series with the entrance, it was not electrolytic but ceramic or polyester, it sounded so good for just being there 2 simple components. Now taking a look at google, can see that the most passive mixers, uses resistors to isolate sources, with values since 10k to even 100K. Other schematics shows a resistor and capacitor in series (see image below) what does that capacitor? and whats some schematics only has a simple resistor? is it easy to calculate its ohm value?.

Is it better using this configuration supposing that the source is weak (coming from cellphone 3.5 mini jack or RCA) and this mixer targets the signals to a pre amp? So I need to from weak sources like iphone, dvd, any RCA output, etc... anybody know whats the best to use in this case? Thanks so much.

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An outgoing resistor must be attached to your schematics, if you need to attenuate the final outgoing signal. This gives you weighted, attenuated, amounts of each incoming signal.

If you want more of a weak signal, reduce its input resistor. This increases its weighting percentage.

A signal's input resistance cannot always be known. Thus we cannot predict that a given resistor network will be satisfactory with your collection of devices.

The capacitor on the input blocks DC and very low frequency rumbling sounds. 100nF is 0.1uF and a film capacitor produces no distortion but a ceramic or an electrolytic capacitor does produce some distortion. An electrolytic also has a problem called "absorption" where is stores some DC voltage even after it has been shorted. The resistors are not passive because they feed the input of an inverting opamp, then the entire circuit is the mixer and the input signals do not affect each other.