# When is it possible to swap expander and compressor?

In the figure below I want to know when is it possible to swap expander and compressor so that the outputs remain the same?

I know in general it's not possible to interchange because neither expander nor compressor are TI but I know in some cases it's possible.

• Don't you want to swap the down-sampler and the up-sampler in the second picture? Currently the two block diagrams are identical so yo have automatically $y_a = y_b$ Jul 24 '20 at 11:21
• @Hilmar, thank you :), I made a mistake, i changed it. Jul 24 '20 at 11:26
• As said, these are down/upsampling or decimation/interpolation; expanding and compression are different things, as far as I know. In which context did you see these two terms used? Jul 24 '20 at 13:24
• @MarcusMüller, this names is used by oppenheim in his book. Jul 24 '20 at 13:43
• Oppenheim's Signals and Systems or Discrete-Time signal processing? Could you tell me the chapter, please? Jul 24 '20 at 13:55