Choosing a Modeler/FRFR
A modeler's main function is to emulate the tone of analog amplifiers; however, they typically also provide a number of other features, such as speaker/mic emulation, a wide range of simultaneous effects, MIDI send/receive, and configurable signal routing. Some are also in a foot controller form factor, allowing control of not only that device but others via MIDI. This means modelers can take a number of roles, serving as all-in-one processors or integrating with other gear. This can make them extremely complicated in some cases, requiring lots of attention to detail and effort to make it work for you. How you plan to use the modeler, how much time you have to learn and tweak it, budget, and quality are the prime considerations to make.
Understanding Modelers
Ideally, modelers are designed to be virtual equivalents of real world gear, and their user interfaces follow such. That said, whenever you are dealing with large combinations of possibilities, unexpected complexities are bound to show up. Modelers can be confusing and frustrating to those more familiar with analog gear.
Modelers operate digitally, using Digital Signal Processing (DSP) algorithms (usually on dedicated processor chips designed for DSP). Some may have some analog elements to tweak the signal before converting it into a digital representation - usually this consists of a pad switch or similar to prevent clipping the input analog to digital (A>D) converter. On the output side, there is typically an analog amplifier (with a volume control) for the analog outputs, after the signal is converted back to analog. This allows you to gain stage it with other gear; however, it is not powerful enough to power speakers. Some may include an actual power amp capable of powering speakers, but most modelers are designed to only provide tone, not power, like analog effects units.
Modern modelers that include multiple independent effects/simulations (most of them), often provide you with a virtual signal path, allowing you to select and order the available effects as you want. The number and/or type of effects allowed in a signal path is often a bit limited, which is necessary for the modeler to maintain real-time performance. If the time required to process x seconds of audio is greater than x, then the modeler would not be able to keep up, adding greater and greater lag between input and output and eventually running out of memory to buffer the audio from the input (or it could drop parts of the audio input). Even the most powerful modelers are capable of reaching a DSP limit and throwing an error if you try to add too many effects, with some effects being more resource-hungry than others.
Some even offer multiple independent virtual signal paths that can process in parallel, allowing audio to be split and merged or even routed to separate outputs. This can get tricky with analog gear, and there are even more potential issues when doing so digitally. Digital algorithms often need to buffer a segment of the input audio before being able to process it, resulting in lag. This is often so short it is unnoticeable; however, when audio is split and processed separately giving the different paths different lag times then merged back together, this can create a comb filter, where some frequencies are out-of-phase, creating "notches" in the frequency spectrum. Advanced processors and DAW software recognize lag differences and resolve them when merging audio, but not all of them do.
While analog gear needs to be gain staged correctly for the best SNR, many modelers need their virtual signal paths to be gain staged even more carefully to avoid clipping. Because the amplitude of the audio is represented as a digital number, exceeding the maximum value will cause overflow. Some modelers may handle this gracefully, subjecting the audio to a form of soft clipping - there is still audible distortion, but it is not raucous. Others don't fare so well, with digital clipping sounding like severe noise and crackles.
Integrating with Other Gear
A large part of confusion with modelers is integrating them with other gear. And a large part of this comes from the numerous ways you can use a modeler. I cover all the ways to hook them up below, but the point here is that many modelers have output modes or similar options to try to help get the best sound for your particular setup. However, these aren't always easy to find in the modeler's interface, and sometimes it's ambiguous as to what they do and which one should actually sound best. Adding more confusion, these often only apply to the cab/mic simulation, which may be turned off or otherwise disabled.
Impulse Responses
Impulse responses or IR's are sound files that represent a transformation of sound caused by some system. They can be used to provide simulations of the reverb of a room, for instance. In the guitar community, they are popular for cab/mic simulation, capturing not only frequency response but phase and resonance information. In a DAW, a convultion reverb plugin is necessary to apply the IR transformation to an input signal. Most modelers provide their own cab/mic block or make it part of the amp block. These typically use IR's, although only a small number allow you to actually import or export the IR's in and out of the modeler.
Ways to Run a Modeler
There are various ways to use modelers, from all-in-one solutions to just replacing this or that aspect of a regular rig.
Effects Only
If you are just using a modeler for effects only, it is essentially the same as a multi-fx unit. You can run it in front your amp to use typical pre-amp effects like distortion pedals, noise gates, compressors, and wah pedals. Or you can place it in the amp's effects loop, using it for post-effects like delay, reverb, pitch-shifting, and chorus. You just have to be careful to gain stage it to avoid digital clipping or any other undesirable distortion due to strong levels between the modeler and amp.
Most modelers provide an fx loop, which can be used in conjunction with the amp's fx loop to create a configuration known as the 4 cable method (see below). This allows both pre and post placement of effects relative to the amp, as well as additional versatility.
Distortion Pedal Replacement
If you use a distortion pedal as your main source of distortion, likely into the clean channel of an amp, you can replace the distortion pedal with a modeler. This gives you the advantage of running a true tube pre-amp simulation in the modeler rather than the analog solid state distortion of the pedal. While modelers typically emulate the complete amp (pre-amp and power amp sections), some have pre-amp only versions that can be used as such. Depending on your real amp, the pre-amp model or the "full" model might sound better than the other. The modeler may also have a "front" mode designed to EQ the signal to be better equipped to hit the front of an amp.
You don't have to abandon your actual dirt pedals - you can place them before or after the modeler and toggle them on/off as desired. Again, just be sure to gain stage things correctly to avoid digital clipping or other unwanted distortion.
Pre-Amp Replacement
A popular way to run a modeler is to send its output into the effects loop return of an actual amp. The modeler provides the pre-amp tone and/or distortion, while the amp supplies the power to make speakers move. While modelers typically emulate the complete amp (pre-amp and power amp sections), some have pre-amp only versions that can be used as such. Depending on your real amp, the pre-amp model or the "full" model might sound better than the other.
In this configuration the modeler can provide both pre and post placement effects - you just need to order them correctly in the virtual signal chain relative to the amp model. You can also incorporate additional pre effects by placing them in front of the modeler and post effects by placing them between the modeler and the amp's effects loop return.
Amp/Cab Replacement
Modelers typically incorporate cab/mic simulation. This allows it to replace a guitar cabinet as far as tone is concerned. This eliminates the requirement of a mic'ed cab for live and recording purposes, as you can go straight from the modeler to the mixing board (and thus into the house PA speakers) or DAW. For rehearsal or jamming purposes, the modeler is just replacing the tone of the cab, not the actual generation of sound waves. Powered FRFR speakers are still required to hear your playing, although these can come in a wide variety of formats, from headphones, to studio monitors, to stage monitors...you can even use a consumer stereo system (just be sure to disable or turn down the subwoofer and tweak the EQ).
This setup requires no extra gear at all - you can plug directly into the modeler from your guitar and out the modeler into the DAW/PA/FRFR speaker. If desired, you can add additional effects in front or behind the modeler.
Cab Replacement
If you intend on using a real amp but want to use a modeler for cab/mic simulation, things can get a little tricky. The amp needs to have an effects loop, and you need to run the send from that to your modeler. Some modelers split the amp and cab/mic emulation into separate blocks - then you can just disable or omit the amp block and use the cab/mic block. Others incorporate them into a single block. It may still be possible to select "no amp" or equivalent from the list of amp models, so you are just using the cab/mic sim. But if that's not available, the best you can do is select the cleanest possible amp model from those provided.
The modeler can provide pre-amp effects by routing the guitar directly to the modeler then using its effects loop to send out to the amp and have the amp's effects loop send output into the modeler's effects loop return. Post effects simply need to be placed behind the modeler's fx loop placement.
4 Cable Method
The 4 cable method is a way to connect a modeler to a real amp using 4 cables. The cables are:
- Guitar > Modeler
- Modeler FX Loop Send > Amp Input
- Amp FX Loop Send > Modeler FX Loop Return
- Modeler Output >
- Amp FX Loop Return or...
- DAW/PA/FRFR speaker
This allows you to run a variety of the ways discussed above and more:
- Use the real amp's pre-amp section
- Use the modeler's amp models
- Use the modeler for pre or post effects, whether using an amp model or the actual amp
- Incorporate additional pre or post effects
- Use the real amp's power section to power a guitar cabinet
Modeler's FX loops are often placeable in the virtual signal chain and can be toggled on/off. This allows some patches to bypass the modeler FX loop which essentially removes the amp's pre-amp from the signal chain - useful when you want to use an amp model inside the modeler. Similarly, the modeler's amp block can be disabled while the modeler's FX loop is engaged, using the amp's pre-amp rather than the modeler's amp models. This gives you full flexibility, allowing you to use amp models for tones your amp is weak at delivering and your amp's tone where it is superior to the modeler's amp models. For example, your amp might have a great lead tone but a so-so crunch tone - one patch uses the modeler for crunch tones while another patch uses the amp for lead tones.
Major Brands/Models
Avid - 11r (Eleven Rack)
The 11r marks Avid's first venture into the modeler market. Despite being recognized for quality tone and ease of use, it has become a relatively undesirable piece of gear. The main complaint is that Avid has stopped supporting it, no longer providing updates and fixes. Also, it will only interface to a computer through Pro-Tools for patch editing and saving, which many users find to be a hassle.
Digitech - RP, GSP 1101
Fender - Mustang
Fractal Audio Systems - Axe FX
The FAS Axe-FX line is considered one of the best modeler lines out there, both in terms of emulating real world gear, but also in the amount and depth of features available. FAS is a small company and the Axe-FX is their flagship product - it gets a lot of attention and support, with numerous firmware updates.
Kemper - Kemper Profiling Amplifier
Kemper is another huge name in this market, despite being relatively new. Rather than take the approach of offering amp models, Kemper allows users to create "profiles" of real world rigs. The Kemper Profiling Amplifier sends a test signal to an amp and mic'ed cab and analyzes the output, creating a profile designed to emulate the entire rig at those specific settings. It is essentially a snapshot of the rig's tone. Profiles can be tweaked like a normal amp model as well. This approach has decoupled the Kemper software development team from designing amp models, with the user community and commercial vendors providing tons and tons of profiles released much more frequently and quickly than is typical for modelers.
LePou - Various VST's
LePou is a programmer who has designed a number of free VST plugins that model real world amplifiers. While the quality and interface deserves praise, the caveat is that it requires a system capable of hosting a VST to use. This makes it nice in the studio but more difficult to take to gigs or rehearsal...or even move around the house. LePou also provided an IR loader called LeCab2, capable of loading 2 simulataneous IR's.
Line 6 - DT, Pod, Spider, Vetta
Line 6 is a big name in modeling with the Pod being the first mass-market modeling success. It has since expanded its Pod line and most of its products use the modeling algorithms found in the various Pod products. The Pod is currently on its 4th generation, with each generation featuring different "engine" as the modeling algorithms change to take advantage of more powerful hardware. Each generation also has several form factors.
Positive Grid - Bias
Bias is a software-based modeler, available on mobile platforms as well as home computers, making it a highly portable solution. Despite its wide platform support, it is also known for its high quality.
Zoom - G
FRFR
Modelers usually include cab/mic emulation. Guitar speakers/cabinets typically roll-off the more extreme high-end frequencies, focusing on midrange. They also have certain resonances and characteristic formants. Using cab/mic emulation is great for home recording, removing the need to mic a cabinet. It also removes the need to crank the volume a guitar amp for its unique tonal additions from its power section, so you can play/record in low-volume situations without sacrificing tone. Unlike guitar speakers, most general-purpose speakers, especially pro audio (PA, studio monitors) are designed to be full-frequency flat-response (FRFR), meaning they output all frequencies (within human hearing) without boosting or diminishing any of them in relation to the input signal they receive. FRFR has become a kind of buzz-word, with many debating just how FRFR an "FRFR" speaker/monitor is. Regardless, using a modeler with cab/mic simulation into an FRFR speaker should get you a tone similar to a real guitar amp/cab rig that has been mic'ed.
The most popular FRFR speakers for pro audio are studio monitors and stage monitors. Studio monitors are typically smaller (5-8" woofers) and are nearly always found in pairs. They are loud enough for playback in a small to medium size room with low noise - a studio control room for instance. For live playing, stage monitors (aka PA speakers) are more popular. DJ's often use pairs of these for smaller venues. For large venues, they are more often used as stage wedges for the band to hear themselves, with a much larger PA system responsible for delivering sound to the audience. While a pair is nice to take advantage of stereo effects/routing, often a guitarist needs just one (most dedicated guitar amps and cabs are mono). These come in sizes and loudness similar to guitar cabinets; however, they are generally lighter and more portable, as well as having a wider frequency dispersion. They are also shaped capable of being laid on the ground as wedges, stacked in towers, or mounted on poles.