Why upsampling would degrade sound quality ?, DAC job vs software job Options

[extrabigmehdi]

I was thinking that the DAC must be doing interpolation itself in order to reconstruct the final smooth signal.
So if we upsample with sox (i.e foo_sox) inside foobar , before the DAC interpret the data, I don't see why the upsampling would "deteriorate" the data, since anyway it would end up by being interpolated by the DAC. I don't understand the usual position I see, "don't upsample", it will just deteriorate data ...I was thinking that on the contrary, that upsampling before on sox, would just do a part of interpolation job before it's finalized by the DAC .
So beside chewing additional cpu cycles, I don't see why upsampling while playing music would be discouraged.

[saratoga]

I was thinking that the DAC must be doing interpolation itself in order to reconstruct the final smooth signal.

Correct.

I don't understand the usual position I see, "don't upsample", it will just deteriorate data

Where do you see this? Properly implemented, upsampling will do nothing at all except waste space.