Pro-Q3 and Impulse Responses
How to use Fabfilters Pro-Q3 as a dedicated IR loader for guitar and bass.
Table of Contents
What is an impulse response?
Maybe you’ve heard the term “frequency response” thrown around before— generally speaking, it pertains to how microphones or speakers reproduce certain frequencies.
Due to physical limitations, differing construction methods and materials as well as a myriad of other factors, microphones and speakers cannot 100% capture or reproduce sound identical to the source. You can get pretty close, but the subtle variations of how the equipment responds to certain frequencies will always give you a slightly innacurate version of the original.
With speakers for instance, an 18" subwoofer speaker reproduces low frequencies very well, but compared to a 2" tweeter the higher frequencies fall off. Speakers have to physically move their diaphragm back and forth, and the ability of an 18" speaker to move with the same speed at those higher frequencies is, in the end, limited by physics.
An 18" speaker cannot reproduce the exact same frequencies as the 2" tweeter and vice-versa.
This is what is being referred to when discussing the frequency response of a given piece of equipment; the inherent characteristics of a piece of equipment reproducing or capturing sound.
If you were to take a perfect sinewave sweep from 20Hz to 20kHz, feed it through an amplifier and speaker, and capture the audio with a reference microphone you’d have, essentially, the frequency response of your speaker. Comparing it to the control audio, you can hear how accurately your speaker reproduces the whole frequency range.
Some extremely smart individuals found a way to condense that information into a small sample file called an Impulse Response which can be loaded into a Convolution Reverb— essentially allowing you to process any audio through your speakers frequency response. The result is nearly identical to the real thing, with even greater control over the overall sound.
Being able to “load” in a new cabinet or audition a whole collection of them to see what fits the track best without having to re-record your take is… amazing. It also completely transforms a DI bass or guitar track— taking it from sterile and lifeless to realistic and natural.
A minor downside to working with impulse reponses is the inherent nature in which reverb operates. No matter what you’ll be adding some delay, and if tracking with a 100% “wet” signal it may feel like input-lag to some people.
Nix the delay
The solution? Use EQ.
A lot of modern software EQs have an “EQ match” function, and you can utilize this to generate an exact EQ curve of your favorite impulse response.
By using 2 tracks with the same source audio, such as white or pink noise, and an impulse response loaded onto one, you can use something like Fabfilters EQ match to analyze the two tracks and create an impulse “curve” preset.
In this tutorial, I’ll explain how to do just that using REAPER and Fabfilter Pro-Q3.
The layout is simple, two tracks with white noise generators— one with an impulse response loaded, and one with Pro-Q3.
In this example, I’m taking a fantastic Gallien Krueger bass cabinet impulse response and using that as my target. Here’s my “IR” track— using ReaVerb, I chose my impulse response file, and set the Wet/Dry balance to completely wet, as well as applying -18dB of gain reduction.
After volume matching both tracks (I went with -12dB), I can begin the track routing. This method involves piping the IR tracks output into the EQ Match track sidechain input, which looks a bit like this:
Pro-Q3’s Sidechain Input
This will look different for each DAW, but the premise is the same. Pro-Q3 will be analyzing the sidechain input, so take a moment to search on how to do that for your particular DAW if you’re not familiar.
Step by step
1. Sidechain Input
With the track routing successfully completed, you can view both tracks within Pro-Q3 at the same time by selecting “Pre+Post+SC” on the analyzer.
The track signal will appear white, while the sidechain input will appear red. Remember, we’re using the same control source on the two tracks, the difference is the impulse response. Already we can see how radically different the curve of these two tracks are.
2. EQ Matching Window
In the Analyzer window, select EQ match at the right.
If your sidechain input isn’t correctly showing up at this point, go back and troubleshoot. Make sure both tracks are playing (maybe mute your monitors) and you should be good to capture both sources.
3. Analyze and match
Record both inputs and you’ll be able to use the “Match >” button once Pro-Q3 has done its thing. It’s pretty quick.
4. Number of bands
Pro-Q3 will give you an EQ curve with an option to choose how many bands you’d like to include. The higher the number, the more complex the curve. I’m a complete mad-man, so I choose the highest possible value at 24. Watch out world.
5. You’re done!
Before saving, I like to use the Auto Gain feature located in the Output section of Pro-Q3. This ensures I don’t have huge volume spikes when auditioning different impulse curves.
This may not be for everyone. There are plenty of fantastic IR loaders out there, some with mind blowing capabilities like crossover options and advanced cabinet blending— I just haven’t found one that I really loved.
I tend to keep things simple, so an EQ curve works perfect for me. Interestingly enough, you can tweak the curves pretty heavily and still retain a “cabinet” sound, allowing for some pretty wild flexibility.
I use Pro-Q3 so much I have a dedicated hotkey to insert/open it up, so being able to use it as an IR loader (essentially) has been pretty great for my workflow.
In the future, I’m considering taking the same track and processing it with a traditional IR loader and the IR curve method and phase-flip testing them to see what the actual difference is. My guess is probably pretty minimal, as both methods sound nearly identical to me.
What do you think? Is input lag noticeable enough on IR loaders or convultion reverbs to warrant this process? For me, kinda, but even if one person out there finds this useful, I’ll chalk it up as a win.
Last modified: May 21, 2021