Creating IRs With Logic Pro X

The Equipment

Studio IRs are relatively not too hard to make with proper equipment, but many studios offer IRs for sale. Basic IRs can actually be made at in-home studios and allow for recreation of mic placements that you really enjoyed and don’t want to lose when you are done recording. 

In order to make an IR you would need the following: 

• Audio Interface – It can be any interface, but it is recommended to either disconnect your monitors or mute any outputs that are not feeding the Reamp box.

• Reamp Box – This is done to turn the output of the interface from High Impedance (Line Level) to Low Impedance (guitar or instrument level). This is done to clean up the signal and is optional.

• Solid State Power Amp or Tube Amp – Depending on what you have available, the power amp section can affect the tone of the IR. Solid State Power Amps have a relatively flat curve and will allow more tonal freedom when reamping. If you are using a Tube amp for reamping it is recommended to create your IRs with a Solid State Power Amp. Tube amps tend to have tonal shaping and will add some color to the IR. In order to use your tube amp, all you have to do is connect to the FX return input and that will bypass the preamp section. 

• Cabinet – every cabinet has a unique tone and things like speaker type and number of speakers can affect the tone. 

• Microphone – Three big things will affect the tone: Mic Type, Mic placement and number of Mics. This is useful to keep in mind when building multiple IRs for a product.

• Microphone Preamp – An optional part to an IR that is often regarded as the secret sauce when it comes to IR creation. This adds a final layer of tonal shaping. 

Creating an IR

The first thing you want to do is open up an empty logic pro file with a single audio track. Your project should look like this:

From there you are going to open the Space Designer plugin located under the reverb section: 

Open the plugin and click on where it says sampled IR. Load any IR. Click on the box where the preset would load and then click on open IR utility

Upon opening it will ask how many Mics and speaker positions you will be doing per IR. Match this with the number of Microphones and Mic placements you will be using. For this example I will be using 1 mic and 1 speaker. Once it loads you should see the following for a 1 mic 1 speaker configuration: 

Under the sweep section, make sure that the channel matches your output to the reamp box. The test tone is a useful way to make sure that the signal is reaching the cabinet. Clicking on the box will send a test tone of the desired frequency (low 100hz, mid 1K, high 10K). Mode determines how slow the frequency increases through the sweep and a longer sweep will yield a higher resolution for your IR (more samples). 

In order to perform a frequency sweep you would need to first clear your current tracks. Click on the record symbol next to the desired Mic track to enable recording and when prompted click record in order to clear all tracks. From there the Sweep button shall be enabled allowing you to capture a frequency sweep. Before performing the sweep, make sure that all your mic tracks have the current input, recording enabled and are picking up the test signal.  

When you perform the sweep, you will see a recoding like the following image:

From there you can hit the deconvolve button and it will transfer it to the time domain and will look like an impulse with a delay like the following:

Be sure to highlight the empty space before the impulse and hit cut to reduce any delay associated with the impulse. 

From there click create setting and name your impulse response. Take note of where the file path is as you will need to convert it into a wav file next.