Rectifying an audio signal

Hello all, this is my first post. I'm examining the electronics of dynamic range compressors, and I can get most of the steps in the signal flow easily except the very first.

I'm trying to rectify an unbalanced AC signal (the audio signal) so both the positive and negative waves are positive, i.e. I have to flip the negative's phase and combine the positive and negative so I essentially get an unsmoothed DC signal.

I know this is easily done with a transformer balanced signal, but I'm trying to do this passively without a transformer – I just can't get my head around how I flip the negative signal so it's positive after splitting it with a pair of diodes, if it can even be done like this.

Can anybody offer any help?

Thanks very much.