Cab block

User contributions

What's an Impulse Response (IR)

• An Impulse Response (IR) is a collection of data representing sound measurements taken from a speaker cabinet or system and used by the Axe-Fx II to enable the Cabinet block to emulate a particular speaker cabinet. A test signal is played through the actual speaker, recorded, and used to generate a profile utilized by the Axe-Fx II to reproduce the measured respons. The Axe-Fx II also uses IRs for microphone simulation. 
• The terms "cab" and "IR" are often mixed up.
• More information in Wikipedia

Nearfield and farfield IRs

• Most IRs represent the tone of a speaker that was recorded with the microphone close to the speaker ("nearfield" or "close-mic'd"). "Farfield" IRs on the contrary represent the speaker sound when there's some distance between the listener and the speaker. See also Close-miked versus amp-in-the-room. There are 3 farfield IRs among the stock cabs, created by Jay Mitchell ("JM").

Matching amps and cabs

• It’s a matter of personal preference which cab model (IR) you want to combine with a specific amp model. You can choose for traditional combinations. Or be creative and innovative. The differences can be huge.
• 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 here: AMP (block): list.

• Legendary Tones: G12M versus G12H
• TGP: EVM 12L versus EVM 12S
• Sound On Sound: Choosing guitar-amp speakers
• Sound on Sound: Understanding and recording guitar speakers
• Guitar Player: 15 12" speakers
• Rivera: 15 speakers compared (YouTube)
• Eminence tone guide
• Fenderguru: Selecting speakers
• Guitar Player: Alnico Taste Test

Cab block: position on the grid

• In the "real" analog world it makes a difference if you put effects before or after the speaker cabinet. It's different with the Axe-Fx II. 
• 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."
• Cliff: "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."
• Cliff: "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
• Keep an eye on the mono/stereo configuration. When placing the Cab block at the end of the grid, set to HiRes Mono or LoRes Mono, the output signal will be summed to mono. And if the Cab block is set to Stereo but it is followed by a mono block (such as Drive), the resulting signal is also mono.
• Cabinet blocks in parallel rows sound louder than a single Cabinet block. Here's the 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

Cab block: HiRes Mono, LoRes Mono, Stereo

• A HiRes (high resolution) Cab block contains an IR consisting of 2040 samples. It requires more CPU capacity than a LoRes Cab block (1024 samples). You can often use a LoRes Cab block without any negative impact on the tone.
• A stereo Cab block contains two LoRes IRs.
• Cliff: "I started out with 8192 but didn't hear any difference so couldn't justify wasting all that space and CPU. You can hear it with room mics but the room simulation sounds nearly identical. There are a couple reasons for 2040. Probably most important is that it allows 1024 in stereo mode. To be able to do stereo 1024 requires a 2040 convolution engine. Secondly, some IRs benefit from longer IRs. Better to have the ability and not need it than the converse." Source1 Source2
• Jay Mitchell's comments on IR resolution: Source1 Source2 Source3 Source4
• If you never need cabinet simulation, for example because you're using the Axe-Fx II for effects only or exclusively with a power amp and speaker cabinet, switch it off in the Global menu. This will decrease CPU utilization in all presets considerably. 

Mic models

• Don't underestimate the impact of the mic type on the tone. E.g., adding a R121 (which is a Royer 121, captured at 6", front) will add lots of highs and lows to the tone. The 57 DYN (Shure SM57) works with almost everything. Many studios and users like to combine the Royer and SM57. Cliff: "I almost always use a mic model on the non-mixed IRs. I'll typically use a 57 on one side and an R121 on the other." Source
• The "None" setting disables mic modeling. But a mic is still involved because the IRs themselves are captured with microphones. Even when a neutral mic is used to capture, such as an Earthworks mic. When capturing IRs, the mic is most often placed very close to the speaker, so the result is a close-mic'd tone. Still, selecting "none" is a good way to prevent adding additional eq-ing to the tone.
• Firmware 3.0 added the Proximity parameter. This simulates the proximity of the recording mic to the speaker. Higher numbers translate to the mic being closer to the speaker (nearfield). Lower numbers translate to the mic being further away from the source, with the lowest number providing far-field coloration.
• Firmware 11 added the Proximity Frequency parameter. This allows tuning the frequency range over which the proximity effect occurs.
• Cliff: "The mic models are actually IRs. The mic IR is convolved with the speaker IR to create a composite final IR." Source

• There's great info about mics in the document Dialing in Your Tone by Red Wirez.
• Wikipedia:
  • Shure SM57
  • Shure SM58
  • Shure Beta 87A
  • Neumann U87
  • Royer R-121
  • AKG D112
  • Neumann U67
• More information:
  • http://www.recording-microphones.co.uk/index.shtml
  • http://www.barryrudolph.com/stellar/guitar.html
  • http://www.gearslutz.com/board/so-much-gear-so-little-time/201972-mic-standards.html
• Additional information in this Wicked Wiki thread.

Factory IRs (stock cabs)

• Cliff: "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
• Selected Red Wirez, OwnHammer and Kalthallen IRs are included with the Axe-Fx II as stock cabs. Also included are some farfield IRs by Jay Mitchell. New: Producer Pack IRs (with "Mix" in their names).
• All stock cabs are time-aligned, which means that you can mix these in the Axe-Fx II using stereo cabs.
• Firmware 10: "Added 35 cabinet models from the first of our “producer packs”. These models are custom blended IRs using multiple mics on the cabinet. Hand-tuned by the producer, these IRs are ready-to-go with little additional EQ required for mix-ready results. The first 30 of the IRs are guitar amp cabinets and the last five are bass amp cabs. Also added several artist IRs including two from James Santiago and one from John Petrucci of Dream Theater."
• The Producer Pack IRs were captured using a mix of microphones (Shure SM57, Royer 121, Sennheiser MD421 and Shure KSM32) and a Neve 1070 preamp.

User cabs (external IRs)

• If you are looking for something different than the stock cabs, try 3rd-party IRs. The Axe-Fx II has "user cab" slots for this purpose. You can upload external IR files into these slots, using Axe-Edit or a MIDI librarian.
• The Axe-Fx II and Axe-Edit will display the name of the IRs in the user cab slots. The name is contained in the sysex data of the IR file with a maximum of 32 characters. IRs can be renamed using Axe-Edit or 3rd party utilities.
• The process of uploading IRs to the Axe-Fx is described in the manual. Also, forum member Cobbler describes the process here. You can also use Fractal-Bot.
• Firmware 10: "Increased the number of User Cabinet slots to 100 (plus one scratch-pad location). Note that the upper 50 are saved in a different area of memory and are not dumped or restored when doing a system dump/restore. A “Scratch-Pad” location has also been added. This dummy location can be used to receive cabinet data but is not saved to non-volatile memory. This allows auditioning IRs without overwriting any of the user slots."

Sources for external IRs

• You can get Impulse Responses (IRs) from these sources, among others:
  • OwnHammer
  • RedWirez
  • Kalthallen
  • Fractal Audio Shop. Note that the Producer Pack files have a different file format, which doesn't let you mix these IRs with known mix utilities. Solution: convert them to .wav first, using this utility.
  • Silent Underground
  •  Axe-Change
  •  Forum thread
• Here's how to create an empty user cab (IR).
  • Use a MIDI utility such as MIDI-OX or Sysex Librarian to receive a dump of an empty slot, using Utility > Preset > Dump User Cab on the hardware.

Room ambience

• Close-mic'd IRs do not contain enough samples to recreate room ambience. That's why the Axe-Fx II provides specific room ambience parameters in the Cab block. This is a dedicated reverb effect, which also works well when using the Axe-Fx with headphones.
• Also see Close-miked versus amp-in-the-room.

LowCut and HiCut Freq

• The Cab block provides low-pass and high-pass controls. These make it easy to tame boomy or harsh sounds. You can also use the same parameters in the Amp block, or use a separate PEQ, GEQ or Filter block. Common settings are 80-150 Hz for high-pass (cutting bass), and 5-7 kHz for low-pass (cutting treble), but YMMV.
• Cliff: "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

Speaker Size

• Firmware 2 introduced Cabinet Size Warping. This allows the user to change the relative size of the speaker. This parameter is accessible only when the Cab is set to Mono. Cab Size was renamed to Speaker Size in firmware 5.

Motor Drive

• This models the effect of high power levels on the tone of the speaker. The Motor Drive parameter controls the relative drive level and, therefore, the intensity of the effect.
• Cliff: "Motor drive isn't EQ. It models efficiency reduction due to thermal effects." Source
• Here's a tutorial by forum member Manny Fufish.
• Cliff: "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
• Cliff: "What I have found is that thermal compression is somewhat noticeable and measurable. This is modeled by the Motor Drive parameter." Source

Air

• The Air parameter mixes some of the signal going into the Cab block with the signal leaving the Cab block. 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.
• 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

• Firmware 6 added the Delay parameter. This is a "micro" delay for stereo application.
• Release notes: "When running a stereo mode, or two cab blocks in parallel, delaying one cabinet 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."

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 Speaker tab (resonance parameters, Speaker Drive) and Thunk.

IR Capture: creating your own IRs

• Firmware 3.00 and later let you create your own IRs.
• Get tips from the following sources:
  • Mini Manual (Cab IR Capture Guide)
  • Example clip
• IR Capture doesn't work when "Copy output 1 to output 2" is enabled.
• Cliff: "The quality of the power amp isn't really that important. As long as the response is flat. The Axe-Fx does some fancy math and removes the distortion from the measurement. Most solid-state power amps are very flat, their distortion performance is usually where they vary." Source
• Cliff: "Mixer is not so important. The IR capture algorithm in the Axe-Fx removes any distortion from the measurement so even a cheap pre is fine. The mic, however, is definitely important."Source
• Cliff: 'The IR is vastly more important. Tone Matching is a nifty feature and certainly useful but you'll get far more satisfaction by concentrating on capturing good IRs. The single most important aspect of recording guitar amps is micing the amp. Therefore the single most important aspect of using your Axe-Fx is the IR. People are too hung up on "matching" or "profiling" an amp but fail to realize that when you are doing that you are basically capturing an IR. If you capture the IR separately now you have an IR that is fully separated from the amp and therefore can be used with all models. Matching and profiling cannot mathematically separate the amp's frequency response from the cabinet frequency response. Once you do this you'll be surprised at how accurate the amp models are. I do this all the time and find Tone Matching is unnecessary now (in fact many of the amp models have had their built-in matching data removed in the latest firmware). Any differences between the model and the real amp are so minuscule as to be immaterial. A little tweak of the tone stack or EQ is usually enough to remove and differences. Besides, once you get into mixing you'll realize that you'll be applying EQ anyways so tiny differences in EQ are irrelevant. Moving the mic just a small amount drastically changes the sound. The best producers have mastered micing. You can only fix so much via EQ since EQ is essentially painting with a broad brush where mic technique is akin to using a fine-point brush. Source
• Cliff: "What an IR won't capture is any speaker distortion and speaker/guitar interaction differences. Speaker distortion is mostly irrelevant though since it is typically much less than the amp distortion. Furthermore, we simulate it anyways. Speaker/guitar interaction causes reinforcement of bass and low mids so playing through a cab at moderate to high volumes will sound slightly different than playing through the IR and listening through monitors or headphones. This becomes more prevalent at higher gains because there is more reinforcement at higher gains (this is why you can get controlled feedback easier at higher gain). The difference is so minute though that it doesn't really matter. It cracks me up that people nit-pick about minute differences when those differences are minuscule in comparison to the difference between the response of two monitors (even two of the same brand and model). You can compensate for the difference in interaction by putting EQ before the amp block and boosting the bass and low mids slightly. Or use big monitors and crank 'em." [1]

Acoustic tone IRs

• To emulate acoustic instruments (acoustic guitar, violin etc.), an IR of an acoustic body can help. You'll find good ones here.
• Acoustic sounds benefit from long IRs so try to keep them HiRes.

Substituting an IR with a Tone Match block

• You can integrate an IR in a preset by replacing the Cab block with a Tone Match block, after having captured the tone of the Cab block. Here's how.

How to empty an user cab slot on the Axe-Fx

• To empty an user cab slot on the hardware, mute all faders (or don't load any IRs) in Cab-Lab and send it to the user cab slot.

IRs for Axe-Fx Standard / Ultra

• IRs for the Axe-Fx Standard/Ultra must be converted to be able to use these with the Axe-Fx II. Source 
• It's no use converting 1024-point IRs to 2040 points because they don't contain the necessary data. You need the original WAV-file to create a 2040 point IR.