A method of retrieving a content using a print medium is disclosed. An example equalizer described herein includes a high frequency amplifier to receive an input signal and to amplify a high frequency portion of the input signal, a low frequency amplifier to receive the input signal and to amplify a low frequency portion of the input signal, and a weight factor controller to control a gain of the high frequency amplifier and a gain of the low frequency amplifier. The references are then reported as pinned to a garbage collector in response to invocation of a garbage collection service.