Examples of common re-amping objectives include taking a pre-recorded electric guitar track and adding musically pleasing amplifier distortion/overdrive, room tone such as reverb, audio compression, EQ/filters, envelope followers, resonance, and gating.
By playing a dry signal through a studio's main monitors and then using room mics to capture the ambiance, engineers are able to create realistic reverbs and blend the "wet" (modified) signal with the original dry recorded sound to achieve the desired amount of depth.
By pointing the monitors away from each other and miking each speaker individually, the stereo image can be well preserved and a new sense of "depth" can be added to the track.
When a desired tone is finally achieved, the guitarist's dry performance is re-recorded, or "re-amped," with all added effects.
On the other hand, if the engineering and production team in 1985 had simultaneously tracked (recorded) a "dry", DI out signal from the electric guitar's pickups, a producer remixing the song 30 years later could take the dry guitar signal and re-amp it through 2000s-era digital effects and speaker systems, giving a new sound to this 1985 track.
Playing back a signal from recording studio equipment directly into a guitar amplifier can cause unwanted side-effects such as input-stage distortion, treble loss or overemphasis, and ground-loop hum; thus there is sometimes a need for impedance conversion, level-matching, and ground alteration.
A re-amping device commonly employs a reversed Direct Inject (DI) transformer with some resistors added for level and impedance shift.
An unbalanced ¼" (Tip-Sleeve) phone connector is typically used for the output, which is connected to the guitar amp rig.
Another approach to simulating the high impedance of a guitar pickup is to use a passive DI and add a 10 K-ohm resistor in series with the signal connection inside a 1/4" plug.
While "reverse DI" re-recording techniques have been used for decades, the process was popularized in part by the introduction of the Reamp device in 1993.
Pierre Schaeffer in the 1930s and 1940s used recorded sounds, such as trains, and played them back with ambient alteration, re-recording the net result.
Sound designer Walter Murch is known for a technique called "worldizing" in which "real world" ambiance is added, via re-recording, to dry recorded program.