A guitar cabinet can be thought of as an acoustic filter, shaping the sound of the amplified guitar by boosting or cutting certain frequencies. Different materials, construction methods, components and so on combine to create a pattern of peaks and dips that give a cabinet its unique sound. If a cabinet has a closed back, for example, it will give you a more bass-heavy response, whereas open-back cabinets offer a brighter, more ‘open’ sound.
That means we can use GUITAR RIG‘s filters and EQs to simulate various physical characteristics of a cabinet – real or imagined. Here’s how to do it in five easy steps.
1: Choose your amp
Start by choosing your favorite amp, and then click on Matched Cabinet to select a partner cabinet. As we’ll be creating our own cabinet here, right-click on it and choose Delete Selected from the menu.
2: Filter out the highs
Good guitar tone is mostly about midrange, so you’ll want to remove some higher frequencies – in fact, many real-world guitar cabinets don’t have any response at all above 5kHz. The Pro-Filter is ideal for this, as it has a low pass filter (LPF) mode, which only allows lower frequencies through. Select LPF in the Mode options and set the Slope dial to its maximum (fully clockwise). This will sharply reduce frequencies above whatever value you choose with the Cutoff dial – try anything between 3.5kHz and 7kHz. If we set the Reso (resonance) dial at around 0.15, we’ll get a slight boost at this frequency which ought to give some improved definition to our notes.
3: Cut the lows
A guitar cabinet typically won’t reproduce frequencies much below 75Hz – that’s desirable for most guitarists, since frequencies below this point typically comprise booming and rumbling sounds that can muddy up a tone. Here, we’ll use a Parametric EQ to replicate this effect.
Open up the EQ controls using the Expert Panel. The low frequencies you choose to remove will depend on whether you use conventional or ‘low’ tunings, but you can safely remove everything below 50Hz. Increasing the Q value widens the effect of the filter. If you choose a high-frequency boost with a wide Q value, you’ll achieve a sound closer to that of an open-back cabinet. A fuller, beefier sound can be created with a boost just above your 50Hz cutoff – approximating a closed-back sound.
4: Tweak the midrange
The variations in a cabinet’s frequency response caused by various peaks and dips is what gives different cabinets their character. Figure 2 shows the result of feeding pink noise (a type of test signal that’s like white noise, but more closely approximates how the human ear perceives sound) through different cabinets to reveal their frequency responses; the two additional stages of parametric equalization can contribute this kind of character to your virtual cabinet.
The upper left image is of a popular amp used by rock lead guitarists. The peak around 2 kHz gives a strong boost to higher frequencies, so leads can cut through a live performance or mix. The upper right image is from a popular combo amp; note the frequency response cut around 1 kHz, an extended high-frequency response, and a fairly even low-frequency response. The lower left image is a high-gain, heavy-metal amp—it gives a relatively uniform response that’s loud across the spectrum. Finally, the amp in the lower right is used by jazz guitarists. The boost around 2 kHz gives good articulation for solos, the bass boost gives a warm, sound, and the midrange dip makes room for piano, vocals, and other instruments that are in the same part of the frequency spectrum.
The second Parametric EQ component can contribute the same kind of “character-oriented” boosts and cuts to your virtual cabinet. For example, if you wanted a sound that’s more suitable for lead guitar, you could use one stage of parametric EQ to add a major boost around 2 kHz. But if an arrangement is fairly dense, then it might be good to take a cue from the jazz amp, and use the second parametric equalizer stage to cut some frequencies in the 500 Hz – 1 kHz range.
You might be surprised how just a little bit of boost or cut at different frequencies can make a huge difference to the overall tone. In fact, the main difference among the three audio examples of virtual cabs involves changes in the midrange EQ.
5: Adjust to taste
The Shelving Equalizer provides a less dramatic tonal change than parametric equalization, so think of it more like the bass and treble tone controls you find on car audio and home audio systems. For example, you can use the high-frequency shelf to boost the highs so the cabinet “cuts” better through a mix, which is almost like adding a virtual high-frequency driver to your virtual cabinet. Or you might want to reduce the highs somewhat for a warmer, more mellow sound that blends in better with other instruments. This would produce an effect similar to switching out a cabinet with a 10″ speaker for a cabinet with a 15″ speaker.
Step 3 used a Parametric EQ Component to do precise editing of the low-frequency response. For more general tone control, the low-frequency shelving equalizer can give a fuller or thinner sound. You can also emulate speaker placement, like boosting the bass to simulate the low-frequency boost that occurs when you put a guitar amp in the corner of a room, or against a wall.
You’ll find that constructing your own cabinet gives different results compared to equalizing an existing cabinet. The technology behind analog filter models and digital cabinet models is different, so the fundamental character is slightly different as well—and now you know how to take advantage of both options, so you can always have the right sound for your projects.