Getting Started with Capture Technology
Getting Started with Capture Technology
Capture technology is a method of creating a digital model of the behavior of real audio equipment or a signal chain.
Instead of programming an amplifier, pedal, preamp, or other device component by component, a capture system measures how the equipment responds to known signals. The resulting data is used to create a model that can reproduce the behavior of the original equipment.
Different systems use different terminology and different methods, but the basic idea is similar: send a known signal through something, measure what comes back, and create a model from the result.
What can be captured?
Capture technology is most commonly associated with guitar amplifiers, but it is not inherently limited to guitar equipment.
Depending on the capabilities of the particular system, possible capture targets can include:
- Guitar and bass amplifiers
- Amplifier and cabinet combinations
- Preamps
- Overdrive, distortion, boost, and other pedals
- Studio equipment
- Analog signal processors
- Combinations of multiple devices
- Complete signal chains
As capture technology develops, its useful applications may extend well beyond the equipment for which it was originally designed.
Capture vs. traditional modeling
Capture technology should not be confused with traditional algorithmic modeling.
A traditional model attempts to reproduce a device using software designed around its known or measured behavior. The developer may model individual circuit stages, components, controls, nonlinearities, speaker behavior, or other characteristics.
A capture system approaches the problem differently. It observes the response of a particular piece of equipment, usually at a particular configuration, and derives a model from those measurements.
This distinction is important.
A traditional model of an amplifier may provide functioning gain, tone, channel, and other controls intended to behave like the original amplifier.
A capture, by contrast, commonly represents the behavior of the equipment at the settings used when the capture was created. Changing those settings significantly may therefore require another capture.
The exact capabilities vary between platforms.
Major capture and profiling platforms
Several technologies are widely used for capturing or profiling audio equipment.
Neural Amp Modeler (NAM)
Neural Amp Modeler is an open-source project that uses machine learning to model nonlinear audio systems.
NAM models can be created by recording the response of equipment to a supplied training signal and training a neural-network model from the resulting recording.
See:
TONEX
TONEX is IK Multimedia's capture and modeling ecosystem. Its Tone Models can represent amplifiers, cabinets, pedals, and combinations of equipment and can be used in TONEX software and compatible hardware.
Kemper PROFILER
Kemper Profiling creates Profiles of amplifier and signal-chain configurations for use within the Kemper PROFILER ecosystem.
Neural Capture
Neural Capture is Neural DSP's capture technology for creating digital representations of amplifiers, cabinets, and drive pedals for use with compatible Neural DSP hardware and software.
Line 6 Proxy
Line 6 Proxy is Line 6's capture technology for creating models of amplifiers, pedals, and other equipment for compatible Line 6 systems.
Open capture technologies
NAM is not the only open technology in this field. Other projects and research efforts are exploring machine-learning approaches to modeling audio equipment.
See Open Capture Technologies.
The basic capture signal chain
Although platforms differ, a typical capture process looks something like this:
Capture software or training signal → audio interface output → reamp/capture interface → device under test → audio interface input → recording or capture software
For an amplifier being captured with its speaker cabinet, a microphone and microphone preamp may also be part of the return path.
For a direct amplifier capture, the signal may instead be taken from a suitable load box or direct output.
The details matter. Levels, routing, impedance, noise, clipping, sample rate, and the configuration of the equipment can all affect the resulting capture.
See Capture Signal Chain.
Calibration and levels
One of the most important concepts in capture technology is level calibration.
The level sent from an audio interface is not necessarily the same level that a guitar pickup would produce. Likewise, different interfaces, reamp devices, capture boxes, and input configurations can produce different electrical conditions.
A capture can sound excellent while still being incorrectly calibrated.
That becomes especially important when models are exchanged between users. If the capture process does not preserve meaningful input and output levels, the model may respond differently in somebody else's system.
See Gain Staging and Calibration.
Reamping
Many capture workflows use techniques derived from traditional studio reamping.
A recorded or generated signal leaves the audio interface and is sent into the equipment being captured. Depending on the equipment and interface, a reamp device may be used to provide appropriate level, connection, isolation, or grounding.
The output of the device is then recorded back into the computer.
See Reamping for Capture.
Captures with and without cabinets
Not every capture contains the same parts of the signal chain.
An amplifier may be captured:
- Directly, without a speaker cabinet
- Through a cabinet and microphone
- With a separate impulse response used for the cabinet
- As part of a larger signal chain
Understanding what is contained in a model is essential when choosing playback equipment and deciding whether an additional cabinet simulation or impulse response is required.
See:
Creating your first capture
Before attempting a first capture, understand the complete signal path.
At minimum, identify:
- What signal the capture system will generate or play
- Which interface output will carry it
- How that signal will reach the equipment being captured
- How the equipment's output will be returned safely to the interface
- Which input will record the result
- What level and calibration requirements apply to the chosen capture system
Do not assume that two connectors which physically fit together necessarily carry compatible signals.
Once the routing is understood, the actual capture or training procedure is usually straightforward.
See Creating a Capture.
Evaluating a capture
A successful capture is not simply one that completes without an error.
Listen critically.
Compare the model with the original equipment using the same source material and, where practical, matched playback conditions.
Useful questions include:
- Does the model have the same overall gain?
- Does it respond similarly to changes in playing level?
- Does the low end behave similarly?
- Are high-frequency characteristics preserved?
- Does distortion develop in the same way?
- Are noise or artifacts present?
- Are the input and output levels sensible?
- Does the model remain convincing with different instruments or source material?
A technically valid capture is not necessarily an accurate one.
Troubleshooting
Capture problems often come from the signal chain rather than the modeling technology itself.
Common causes include:
- Incorrect routing
- Incorrect input or output selection
- Clipping
- Signals that are too low
- Incorrect calibration
- Unwanted cabinet or speaker simulation
- Ground loops
- Excessive noise
- Sample-rate or recording configuration problems
- Equipment changing state during the capture
- Incorrect trimming or processing of training recordings
Learn, experiment, and share
Capture technology is developing quickly. Documentation explains how a system is intended to work, but practical experience often reveals details that documentation does not.
Experiment carefully. Document your signal chain and settings. Compare results. When something works particularly well—or fails in an interesting way—share what you learned.
The NAMFORUM discussion forum exists for exactly that purpose.
The forum is where we discuss and experiment. The Wiki is where useful knowledge can become a lasting reference.