Cab block

The information on this page supplements the official manuals.

Cabinet modeling: supported by which Fractal Audio products?

• Axe-Fx II: yes.
• AX8: yes.
• FX8: no.

X/Y switching in the Cabinet block

The CAB block supports X/Y switching.

About Impulse Responses (IRs)

The Impulse Responses (IRs) page provides information about IRs, including resolution (Ultra-Res and others), difference between near-field and far-field, and more.

IR Capture lets you create IRs yourself with suitable hardware.

Disable and enable cabinet modeling

If you never use of cabinet modeling, turn it off in the Global menu. You'll have more CPU room.

You can also leave out the Cab block per preset. Or bypass it, but this will not decrease CPU usage.

Factory cabs (stock cabs)

Number of stock cabs per device:

• Axe-Fx Mk I/II: 132
• Axe-Fx II XL and XL+: 189
• AX8: 189

All stock cabs are time-aligned, which means that you can mix them using a single Stereo cab or dual Cabs blocks.

Detailed list of all stock cabs

Fractal Audio:
"The factory IRs were hand-selected by me after auditioning thousands of OH and RW and other IRs. Some of the IRs are custom mixes of mine. My rule-of-thumb was to select as neutral sounding IRs as possible. However, what I like may be much different than what others like. Some people complain the Axe-Fx sounds too bright. Others say it's not bright enough. It's a no-win situation. This is why I've been harping on capturing IRs. It's personal preference. Producers probably spend more time perfecting mic placement than anything else when getting guitar tones to tape. An IR is the same thing, it's capturing the mic and placement." source

To get a list of the stock cabs used in presets, use FracTool.

Other free IRs

Some commercial manufacturers provide free IRs. There are also quite a few popular IRs available in the public domain. Some examples:

• "gtrbody": adds the resonant sound of an acoustic guitar body (Axe-Change)
• "cello_body": adds the resonant sound of a cello (Axe-Change)
• IRs created by Fractal Audio, in a session with Larry Mitchell, available here
• GuitarHack ThisOne V30 (Axe-Change)

Matching amp and cab models

It’s a matter of personal preference which Cab you want to use with an Amp model. You can go for traditional combinations. Or be creative and innovative. The differences can be huge. Cab selection often has more impact on the tone than choosing a different amp model!

When comparing cabs, don't judge too quickly. Each time you select a cab, you may need to adjust the amp settings to dial in a tone.

Common combinations of amps and cabs are listed in the wiki and in Yeks Guide to the Fractal Audio Amp models.

Mono or stereo output from the Cab block

Keep an eye on the mono/stereo configuration. The Cab block will sum the incoming signal to mono, unless it's set to Stereo mode or when using two (panned) Cab blocks to handle the left and right sides.

When a Cab block in Stereo mode is followed by a mono effect, such as Drive, the resulting signal will be summed to mono.

Position of the Cab block on the grid

In the "real" analog world it makes a difference where you put effects: before or after the speaker cabinet. It's different with the Axe-Fx II and AX8.

Javajunkie: "You can place the effects loop anywhere in the chain (just add the fx loop block). Unless you are running a stereo cab or 2 mono cabs panned hard L/R, you may want to place stereo effects after the cab. The cab is a linear time invariant effect (unless you add drive) so effects like delay and reverb will sound the same before or after it. As Cliff and others have stated on numerous occasions LTI effects can be placed before and after each other and they will sound the same. Only when placed before or after non-LTI effects (drive, amps, et. al) it really matters. The one caveat there is that some effects are mono, placing effects before and after that makes a difference."

Fractal Audio:

• "The difference in having the cabinet before or after the effects is usually subtle. It depends on how non-linear or time-variant the effect is. For effects like EQ, which are linear and time-invariant, it doesn't matter at all. For slightly time-variant effects like chorus and flanger the difference isn't very pronounced. For highly time-variant effects, like pitch shifting, the difference can be marked."
• "Linear means that the output is related to the input by a straight line: y = mx + b. Filters are example of linear systems. A cabinet IR is a filter. Distortion is an example of a nonlinear system. Linear systems are associative and commutative. Associative means that a * (b * c) = (a * b) * c. Commutative means that a + b = b + a or a * b = b * a. Therefore you can do cab -> eq (a * b) or eq -> cab (b * a). The cab block is "completely" linear if motor drive is non-zero but it is "wide sense stationary" so you can treat it as linear." source
• "The cab block is level-dependent if the Motor Drive is non-zero. So if you turn up/down the level out of the amp block you may need to compensate by doing the opposite with the Motor Drive." source
• "You gain nothing putting it before the cab and risk collapsing the stereo image if the cab is mono." source
• "Since a cabinet is linear (or mostly linear) the order is unimportant as linear systems are commutative (a+b = b+a). However if the cab block is mono your effects will collapse to mono if placed before." source

Cabinet blocks in parallel rows sound louder than a single Cabinet block. Explanation. Bakerman: "It depends on how you're panning. Assuming a mono signal sent to cabs: Stereo cab w/ Pan L and Pan R fully left & right will be the same output level as 2 mono cabs w/ balance L & R. If pans/balances are centered the 2 mono cabs will be 6 dB louder. Balance elsewhere would be between 0 and 6 dB louder, and balance doesn't correspond 1:1 to pan L/R for the same placement. Balances will need to be further toward -50 or 50." source

User cab slots for external IRs

If you are looking for something different, try external IRs. The Axe-Fx II and AX8 provide user cab slots which can be filled with IRs, using Fractal-Bot, Cab-Lab, Axe-Edit or a MIDI librarian.

Number of user cab slots:

• Axe-Fx II Mark I and II: 100
• Axe-Fx II XL and XL+: 1024
• AX8: 512

The Axe-Fx II, AX8 and software editors display the names of the IRs in the user cab slots. The name is contained in the sysex data of the IR file. IRs can be renamed using the editor or Cab-Lab. The name is shown in italics when it's Ultra-Res.

To empty an user cab slot on the hardware, use the software editor or Cab-Lab. The Utility > Preset or Utility > Erase menu provides an easy way to delete ALL user cabs.

Scratch-Pads

Scratch-Pads (the very last user cab slots) are "dummy" locations which can be used to load IRs but which are not saved to non-volatile memory. This allows auditioning IRs without overwriting any of the user slots.

Substituting an IR with a Tone Match block

When you use an external IR in a preset and want to share the preset, you need to share the preset as well as the IR. There are two ways around this:

• Integrate the external IR in an Axe-Fx II preset by replacing the Cab block with a Tone Match block, after having captured the tone of the Cab block. Here's how.
• Create a Preset-Cab bundle, see below.

It's NOT permitted to share commercial IRs (license violation).

Preset-Cab bundles

Read this: Preset-Cab bundles.

Recording 4 different CAB signals

This YouTube tutorial by G66 shows how to create 4 separate cabinet signals in the Axe-Fx II, which you can mix at will. It comes down to using two stereo CAB blocks, with one of the blocks connected to a FXL block to feed Output 2. In both CAB blocks the IRs are panned hard left and right. The stereo outputs 1 and 2 are connected to 4 separate channels on the mixers.

Cab-related parameters in the AMP block

The Amp block has a couple of parameters which are closely related to the Cab block. Check the SPKR tab in the Amp block.

See which cabs are being used in presets

FracTool polls the Axe-Fx II or AX8 and shows a list of the cabs that are used in presets. It also shows which user cabs are not being used in presets, so you can decide to delete these (or not).

Microphone modeling

Read this: Microphone modeling.

Cab block parameters

Input Select

This parameter lets you select the source signal that enters the Cab block. For example, if you wish to run two panned Cab blocks in an Axe-Fx II preset, you can use this parameter to force one side of the signal to go into one Cab, and the other side into the other cab, for stereo separation.

Room ambience

The Axe-Fx II provides room ambience parameters in the Cab block. This is a dedicated reverb effect, which works well when using headphones or IEM. Not supported on the AX8. It turns a mono signal into stereo.

Low Cut and High Cut Frequency

Most IRs have been captured "close-miked", and produce a lot of high and low end material. High Cut and Low Cut Frequency in the Cab block (low-pass and high-pass) allow you to EQ this, preventing boomy bass and harsh sounds. Equivalent to using EQ controls on a mixing board, to position the guitar sound in a mix. These are very important parameters. Default value of High Cut is 10 kHz (Quantum 7 and later).

Common settings are 80-150 Hz for high-pass (cut bass), and 5-10 kHz for low-pass (cut treble) but YMMV.

The “Filter Slope” parameter selects between first-order (6 dB/octave) or second-order (12 dB/octave) filters for Low Cut and High Cut.

Fractal Audio:
"Using Low Cut in the Cab block is akin to what you would do in the studio to carve out room for the bass player." source

Fractal Audio:

• ""LOWCUT FREQ" in the cab block sets sets the -3dB point of a highpass filter at the output of the cab block." source
• "If at the min/max the filters are off." source
• "People often talk about applying low cuts and high cuts. This is because the cabinet models used in modelers are almost always (with a couple exceptions) based on near-field samples of guitar cabinets. IOW, the mic is pushed up against the grill cloth. This just happens to be the way that record producers/engineers mic a cabinet in the studio and the way guitar cabs are mic'd on stage. This is done primarily for isolation reasons. The downside of this approach is that the resulting tone will have a lot more lows and highs than when listening to the amp+cab "in the room". What the mic "hears" when pushed up against the grill cloth is not the same thing that we hear standing 10 feet away. The most common technique to deal with this is to simply cut out the lows and highs using blocking filters, e.g. highpass and lowpass filters. Producers routinely do this when mixing as excessive amounts of lows and highs will cause the guitar tracks to get "lost in the mix". Live sound engineers often do the same thing. The Cabinet block has blocking filters built in for just this very reason. You can also use a couple dedicated filter blocks or a parametric EQ block. For now let's use the Cabinet block. My personal settings are Low Cut around 80 Hz and High Cut around 7500 Hz and Filter Slope set to 12 dB/octave but these are just a starting point. Far-field IRs are available but they are rare due to the difficulty in obtaining them. They require a large facility and special techniques making the process impractical in most cases. So, until an abundant source of far-field IRs are available we need to think like a producer/engineer who is dealing with the mic pushed up against the grill cloth. This means shaping the tone with EQ to remove unwanted frequencies." source

De-Phase

This parameter controls a sophisticated process that removes the “phasiness” from IRs and can yield a more “in the room” experience. This is especially helpful when using multiple IRs. Cab-Lab can apply De-Phase when mixing IRs together.

The processing required is extreme and the control can have some lag. No extra CPU usage or audio latency, however, is incurred.

Not supported on the AX8.

Fractal Audio:

• "Close-mic'd speakers can sound "phasey" because you are in the near field. When sampling the near field of any source the frequency response and beam pattern is rough. This occurs due to multiple spherical waves arriving at various phase angles. These multiple waves come from the various modes of the speaker, internal cabinet reflections and from other speakers in the cabinet. In the far field the response is more uniform because the wavefronts get flatter and the phase angles converge. The De-Phase parameter removes some of the phasiness due to multiple wave arrival using a complex FFT technique." source
• "The higher the setting the more "character" you remove. De-Phase removes some of the character but that's precisely what you want to do as a cab has less character in the far field." source
• (Why is De-Phase necessary?) "You don't listen to a guitar speaker with your ear against the grill cloth." source
• "It's so simple that even experts in the field don't realize why it works." source

Motor Drive

This parameter was present in the amp block as well, before Quantum 9. Quantum 9 replaced it with Speaker Compression. Motor Drive is still present in the Cab block (Axe-Fx II only). It models the effect of high power levels on the speaker.

Motor Drive was Revised in Quantum 7.0:

• "Improved Motor Drive algorithm. New algorithm more accurately models the compression of guitar loudspeakers by factoring in the reactive aspects of the compression.
• "The Motor Drive simulation is available in both the Amp block and Cab block now. It is recommended to use the simulation in the Amp block when using an FRFR configuration as the Amp block simulation uses the speaker resonance information in the calculations whereas the Cabinet block uses fixed values. When using a conventional guitar cab, or a hybrid configuration with monitoring via a conventional guitar cab and speaker emulation to FOH, the Motor Drive in the Cabinet block can be used instead. The simulation in the Amp block also has the advantage of being independent of the block’s output Level control."
• "Gain monitoring of the Motor Drive is available on the MIX page of the Cabinet Block and the PWR DYN page of the Amp block. In the case of the Amp block the monitoring is available when the Motor Drive parameter is selected. Note that typical guitar speakers have around 3-6 dB of compression when driven hard with American speakers being on the low end of that range and British speakers being on the high end. Some speakers can exhibit even more compression than this with compression amounts of 8 dB or more depending upon the magnetic materials used and the construction of the speaker motor."
• "The thermal time constant of the virtual voice coil is adjustable using the “Motor Time Const” parameter. Typical guitar speakers are anywhere from 0.05 to 1.0 seconds depending upon the mass of the voice coil and the materials used."
• "Set it to 4.5 and rip the knob off." source

When using two Ultra-Res cabs in a preset, don't use Motor Drive with just one, because this will cause a hollow sound.

Fractal Audio:

• "Motor drive isn't EQ. It models efficiency reduction due to thermal effects." source And: "What I have found is that thermal compression is somewhat noticeable and measurable. This is modeled by the Motor Drive parameter." source
• "Motor Drive will cause compression if not set to zero (as it models driver compression). Otherwise the cab block is completely linear and will not cause any compression." source
• "Motor Drive simulates power compression due to voice coil heating." source
• "Guitar loudspeakers are intentionally designed to compress. FRFR speakers do compress a bit but not nearly to the extent that guitar speakers do." source
• "Makes edge-of-breakup tone stupid easy." source
• "Speaker Drive models the magnetic compression (which is actually distortion) that occurs due to the nonlinear speaker excursion vs. applied voltage. Motor Drive models the change in power transfer due to heating of the voice coil. When the voice coil heats up the speaker sensitivity decreases, in some cases quite dramatically." source
• "The thermal time constant of a typical guitar speaker is about 0.52 seconds. Magnetic time constants are zero." source
• "So what I've done for the final release is put Motor Drive in BOTH the Amp block and the Cab block. If you're strictly FRFR then you can use the Amp block. If you are using a conventional guitar cab or a hybrid configuration (convention cab for monitoring and direct to FOH) then you can use the Cab block. Doing it in the Amp block also has the advantage that the speaker resonance information in the Amp block is used to calculate the frequency dependent heating whereas the Cab block uses a fixed set of data that is representative of a typical speaker. Finally I've made the time constant adjustable. I did some more calculations and measurements and found that a typical guitar speaker is actually lower than what I had previously calculated because thinner wire is used than I was assuming. Regardless you can now set the thermal time constant to get whatever response rate feels best. When using the Motor Drive in the Amp block it's before the output Level control so you don't have to worry about the behavior changing when you adjust the Level knob." source
• "The actual value for a particular speaker is all over the map. The time constant is proportional to the mass and the thermal resistance of the voice coil. Both these values can vary widely. 200 ms is based on a typical theta of 1 degree C/W and a mass of 10g." source
• "The formula is tau = M * C * theta where M = mass, C = specific heat of the voice coil material (typically copper) and theta = thermal resistance between the voice coil and the magnet gap." source

Air

The Air parameter mixes some of the "direct" signal entering the Cab block with the processed signal leaving the Cab block. This adds some "air" to the sound.

The Air Frequency parameter lets you adjust the cutoff frequency of the mixed signal. Increase the Frequency to its maximum value for a straight mix.

Not supported on the AX8.

If you want to listen to just the Air'd part of the signal, set the Cab to an empty user cab, and turn up Air.

Delay

This is a "micro delay" for stereo applications. When running a Cab in Stereo mode, or when using two panned Cab blocks in parallel, delaying one side relative to the other can achieve interesting comb filter effects. A common practice in studio recording is to use multiple mics on a speaker at different distances to intentionally introduce comb filtering.

Fractal Audio:
"My secret to realistic cab sounds is Delay. Use two IRs in stereo or two cab blocks and put a small amount of delay on one (using the Delay parameter in the Cab block). I like around 0.06 ms. You may like more or less. Producers experiment with placing mics at different distances to enhance the recorded guitar tones. This is the same as using a small amount of delay. Adding a bit of delay introduces some comb filtering which creates notches and peaks in the response which, in turn, adds a sense of "space" to the tone. Try it." And: "If you have any cab packs try mixing the "Back" IR with one of the regular IRs. I use more delay when doing this, 0.1 ms or more. I lower the level on the back IR by a couple dB. This gives a nice "in the room" open-backed cab sound." source

GM Arts:
"This is about mixing 2 signals: one without delay, and the other with a very short delay. 0.06ms is way too short to be perceived as a repeat; the effect is filtering caused by mixing these two signals. To keep things simple, we’ll apply an equal mix of the same signal and another delayed by 0.06ms. An easy way to experiment with this in the Axe-FX is with a Flanger block, with depth and feedback set to zero, and mix set to 50%. Adjust the delay to 0.06ms (not 0.6ms) to hear the effect with a mono signal. This produces a notched frequency response with complete signal cancellation just above 8KHz, with the -3dB point one octave lower at just over 4KHz. The signal is restored over the next higher octave (8KHz to 16KHz), but bear in mind that most IRs will not have much response there anyway, so this effect is mostly a blocking filter over the range 4KHz to 8KHz. So if you have a cab IR that has some response over this range, it will be perceived as a loss of some treble response. For many, this will remove harshness in a way that’s difficult to achieve with other filters. Others may find this effect too much. You can soften this effect by decreasing the delay and/or changing the mix ratio. Decreasing the delay raises the frequency at which this cut occurs. For example, a 0.05ms delay blocks response over the octave 5kHz to 10kHz. Lowering the mix % decreases the depth of the notch. Similarly, applying a delay to a different IR than the un-delayed block will “jumble” and reduce the final response to some extent. If you increase the delay (typically from 1ms and above), you’ll hear the combing effects as multiple notches become low enough to hear in the range of “guitar frequencies”. This sounds like a flanger or chorus without modulation, which shouldn’t be a surprise given we’re experimenting with a Flanger block. So why does this delay sound produce a tone more amp-like? Most players prefer their amp tone off-axis, meaning that they’re avoiding the direct harsh sound directly in front of the speaker, where high-frequencies are beamed. This filter simulates that effect. It’s also similar to standing slightly off-axis when using multiple speakers. Sound travels at roughly one foot per millisecond, so there is a very short delay between sound from different transducers. As Cliff stated, it also emulates recording techniques with mics placed at different distances from the cab. How to calculate? To find the frequency where this rolls-off high frequencies at -3dB, it’s simply: Hz = 1000 / 4 /delay in ms. So for 0.06 ms: 1000 / 4 / 0.06 = 4167Hz. Complete cancellation occurs at double this frequency, 8333Hz, and builds back to -3dB a double this frequency again, 16666Hz. Bear in mind that with higher delays, there will be audible effects from additional notches above this calculated frequency." source

Preamp simulation

Read this: Cab preamp simulation.

Fractal Audio:

• "The VU meter shows the level into the pre. Select a pre Type and turn up the Drive. As the VU approaches the 0 dB marker you will begin to overdrive the pre." source
• "Probably not something you would use for clean sounds. A common technique for rock music is to push the pres, console, tape, etc. to varying degrees to get compression and "sparkle". The trick is getting just the right amount. Too much and it sounds raspy and nasty." source
• "0 on the VU meter indicates onset of clipping. It's not the same as your plug-ins in that regard. The problem with plug-ins is that you don't know where the onset of clipping is since the headroom isn't specified. Our way is superior since 0 dB indicates the point where things are clipping. The other way you have no idea where things start clipping. So 0 dB on the Axe-Fx is NOT equivalent to 0 dB on a typical plug-in." source
• "I've done a lot of testing with isolation cabs. The big thing that happens is that the mic distorts, especially when using an SM57. This adds some crispness to the high end and some compression. I've found that I can duplicate that effect very closely by using the FET I preamp type in the Cab block and turning the Drive up until the desired compression is achieved. I set Sat to zero." source

Speaker Size

Size Warping allows the user to change the relative size of the virtual speaker. This parameter appears only when the selected IR is non-Ultra-Res and the Cab block mode is set to Mono.

This parameter is not supported on the AX8.

Tutorials and more information

• Danny Danzi: the power of a cab block
• Forum member jma has created a handy reference guide, covering AMP and CAB block parameters and descriptions, MIDI CCs, Drive block descriptions etc.
• Premier Guitar: how a speaker cabinet influcences your tone