IR Capture

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The information on this page supplements the official manuals.

Miced cab.png


IR Capture: supported by which Fractal Audio products?

About IR Capture

Read more about Impulse Responses (IRs)

The process to capture an IR is explained in the IR Capture Guide.

Fractal Audio:

Example of a captured IR

How to capture an IR

IR Capture.png

Fractal Audio:
"The method used to capture IRs is set in the Global menu. Mic Only is the traditional method and uses a single input into Input 2 Left as the response from which the IR is derived. Mic + DI uses both Input 2 Left and Input 2 Right. The mic response (i.e. preamp output) is input into Input 2 Left as usual while the output of a DI box (or DI output on an amp) is input into Input 2 Right. Both responses are captured and the response from the Right input is used to correct the response from the Left input. This accomplishes the same thing as using Reference Compensation in Cab-Lab but is done at capture time rather than during post-processing. The advantage to the Mic + DI technique is that it allows almost any amp to be used. A flat, solid-state amplifier is not required. Any amp, whether solid-state or tube, with or without integrated preamp can be used. For example a tube guitar head can be used as the “power amp”. You can even plug right into the front of the head (as opposed to using the power amp input or effects return), even if the head is set to heavy distortion. The unique capture technique of the Axe-Fx removes any distortion from the measurement and completely separates the amp response from the speaker response yielding a pure and accurate IR. To use the Mic/Line + DI method do the following:

  1. Connect the line output of your mic preamp to Input 2 Left.
  2. Connect a DI box between the amplifier output and speaker input. Be sure to use a DI box that is specifically designed to work with speaker level signals and one that does not have any on-board cabinet emulation. You can also use the DI output of your amp if it has one as long as it is not a speaker emulated output.
  3. Connect the output of the DI box to Input 2 Right.
  4. Connect Output 2 Left of the Axe-Fx to the input of the amp.
  5. Set the IR Capture Method in the Global menu to Mic + DI.
  6. Set the Input 2 Mode in the I/O->Audio menu to Stereo.
  7. Capture the IR as usual either using the front panel or Cab-Lab.

Superior results may be obtained using the line out of an attenuator with the attenuation turned off since the frequency response will typically have more low frequency extension than common DI boxes.

Some amps have DI or slave outputs that are simple resistive dividers and work great for this purpose. These include:

Note that in step 2 of the capture process, you should use a speaker cable (between Amp Out and DI In). In step 4 you can use a Humbuster cable (between Axe-Fx Out and Amp Input."



Direct Inject (DI) boxes

Suitable DI boxes for capturing IRs include:

Background information on DI boxes

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