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.

Ways to Run a Modeler

4 Cable Method

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

Fractal Audio Systems - Axe FX

Kemper - Kemper Profiling Amplifier

LePou - Various VST's

LePou is a programmer who has designed a number of 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 - Pod

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

Zoom - G

FRFR

Modelers usually include cab/mic emulation. Guitar speakers/cabinets typically roll-off the more extreme high-end frequencies, focusing on midrange. Using cab/mic emulation is great for home recording, removing the need to mic a cabinet. It also removes the need to crank a guitar amp, so you can play/record in low-volume situations. Unlike guitar speakers, most speakers, especially pro audio (PA, studio monitors) are designed to be full-frequency flat-response (FRFR), meaning they output all frequencies 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.