Reamping

Reamping is a recording technique that uses a recorded "raw" signal as input to re-record a processed signal. This decouples the artist's performance from the settings of the gear dialed in at recording time, enabling changing the instrument's tone without having to worry about inconsistent performances or even the availability of the performer. The practice is popular for recording guitars, which is where it gets its name - the raw guitar signal is sent back through an amp to re-record.

Example Use Cases

• After 20 takes, you finally lay down a difficult solo perfectly. But halfway through the solo, a studio assistant trips on a cable, moving the microphone position on the guitar cabinet and killing the tone (or other random crap like amps blowing fuses, someone making noise while recording, power surges, etc.). Instead of taking another 20 takes to get it perfectly again, you can just reamp the good take.
• You lay down 4 tracks of guitars for an intricate riff. After listening to the playback in the mix, you realize the guitar tone was too distorted and the quad tracking sounds too "mushy" (or you think a different amp will provide a better tone, or you want to add a compressor/noise gate, etc.). Rather than concentrating on playing, you can re-amp one of the tracks without actually recording, adjusting the amp's gain during re-amping to dial in the perfect setting. Then you can re-record all the tracks with that setting using re-amping.
• You are having trouble playing a passage that involves quickly footswitching pedals and/or manipulating a volume/wah pedal. You can record the part without touching the pedals at all, then re-amp it and focus on the footswitches while re-amping.
• You want to make a tone demo comparing several amps and/or effects. You want the playing to be 100% identical to minimize any perceived differences being attributed to inconsistent performances. You record one take with a dry signal and re-amp it for each demo clip, eliminating any possible performance variation.
• You have an artist whose part you want to record, but he is on a very tight schedule. You can get him in the studio, quickly set up a rig for him, and get him recording with a rudimentary tone. He records his part and leaves. Or he records his part elsewhere using his own gear without worrying about mic'ing his amp and sends you the DI track. You can then re-amp his playing for as long as you need to find the ideal tone, without requiring him to be physically present.

Required Hardware

There are two common pieces of hardware associated with re-amping: a DI box and a re-amp box. Some products feature both DI (direct input) and re-amp capabilities.

The DI box is used to split your unprocessed (dry) input signal; so you can send it to your DAW as well as your amp. Most DAW interfaces are not designed to accept high impedance signals like a dry guitar - the DI box serves to buffer and tranform the signal into one that the DAW can easily accept, with minimal noise and clipping. It may also include a means to lift ground, preventing ground loop hum. It also typically coverts the signal from unbalanced (using a 1/4" TS jack) to balanced (using an XLR jack).

A re-amp box does the opposite - it converts the low-impedance, high-amplitude, balanced signal that is output from your audio interface into a high-impedance, low-amplitude, unbalanced signal that guitar amps expect. It can lift ground to avoid a ground loop between the amplifier and DAW. These typically have a level controller to ensure you are sending the amp a level consistent with your guitar's output.

The necessity of these devices depends on your DAW's audio interface and the amp you will be re-amping through. Many interfaces incorporate high Z (high impedance) inputs capable of receiving a direct guitar signal without unwanted noise or distortion. This may eliminate the need for a DI box, depending on how well the interface accepts such a signal. While DAW interfaces don't typically output a high impedance signal, this might not be necessary. Most amps are high impedance, accepting both low and high impedance signals without distortion. However, wah pedals and older distortion pedals are typically lower impedance and respond differently to low vs. high impedance signals. If you are running straight into an amp, there may be no perceivable difference from using a re-amp box.

Also, if you are using a digital device it may connect digitally to your DAW, bypassing any need for DI/reamp boxes. With both my Pod HD and Kemper Profiling Amp, I did not need either.

Recording a Dry Signal or DI

Most performers find it difficult to lay down a good track while listening to their playing only as the completely dry signal. So they split the signal, such as through a DI box. One side goes to the amp. The performer may be in the studio with the amp and hear it directly, or it may be mic'ed and sent to the DAW, where he hears it through headphones or monitors. The other side of the dry signal goes straight into the DAW. The track used to record the dry signal is muted to prevent it from distracting the performer.

When recording the dry signal, you may want to record the wet signal also. It may turn out that there is no need to re-amp, as the tone was perfect the way it was originally set up. In any case, it also makes a good baseline for comparison against re-amped tones.

Reamping Process

To re-amp, the DAW track with the dry signal must be set to output to one of the interface's outputs that can be connected to the amp instead of the normal stereo output bus or the output for the DAW's monitors. The actual output used shouldn't matter so long as the dry signal is the only track using it. Make sure the track is unmuted - this is necessary for the DAW to send it out the selected output.

Recording the re-amped signal is no different from recording any signal - align the DAW track input with the input used on the interface and record arm the track. When you press record, the DI track will output the DI signal to the amp where it will return to the DAW and get recorded on a separate track.

Walkthrough

1. DAW track 1 has a recorded DI track. Its output is set to Line Out or SPDIF Out. It is unmuted, but has direct monitoring disabled.
2. The interface's Line Out or SPDIF Out is connected to the appropriate input on the amp or modeler. The amp/modeler has all switches set up to allow that input to function.
3. Pressing play in the DAW should generate output from the amp/modeler. This can be heard from the cab attached to the amp or headphones plugged directly into the modeler.
4. The mic cable from the mic'ed cab or line out/SPDIF out from the modeler is plugged into the appropriate input on the audio interface. You should be able to see audio in the interface's control panel/mixer for that input when playing back the DAW track.
5. DAW track 2 will record the reamped audio. Its input is set to the audio interface input from the above step. Its output can be the master bus or a group track. It is record armed.
6. Press record. Track 1 will output to the Line/SPDIF out connected to the amp/modeler, which outputs back into some input on the interface, which is captured in track 2.

Caveats

Recording the DI requires an analog to digital (A>D) conversion. Sending it back to the amp requires a D>A conversion. This adds two additional conversions to the entire signal chain vs. recording straight guitar > amp > DAW. Many consider A>D and D>A conversions to degrade the signal. With high quality converters, the degredation is insignificant to most listeners.

While re-amping is designed to ultimately save time (for most use cases), if done improperly or excessively it will increase the time one takes to master a piece. When recording DI's, one should also record the wet signal. There are likely numerous cases where the time to setup your DAW/gear and re-amp are simply not worth the effort given the quality of the original recording. Also, make sure to monitor your wet signal, even when recording DI's that you intend to re-amp. It is difficult to determine whether you performed a good take when monitoring the dry signal, especially if you are not monitoring the wet signal at all. You may end up re-amping a poor quality take or throw away a good take before attempting to re-amp it, both of which will waste time.