Amp and Cab modeling for beginners
Preamps and power amps
Most traditional guitar amplifiers consist of a preamp and a power amp. The preamp is responsible for tone and gain, the power amp makes things loud and may add some distortion and character of its own to the sound.
The Axe-Fx series and AX8 model both: they provide "virtual" guitar preamps and power amps, combined in Amplifier models. Many heads, combos and racked preamps have been modeled.
The processors also provide many other effects, they can "reamp" a recorded dry signal, create Tone Matches of real amps and recordings (Axe-Fx only), capture Impulse Responses (Axe-Fx only), and more.
Traditional guitar speaker (with power amp) or full-range amplification (FRFR)
An amp, whether real or virtual, needs a speaker to sound good. And amplification is required to make modeling loud . Usually this means using either a traditional guitar cab with a power amp, or a so-called FRFR monitor.
- Traditional guitar cab and power amp
A traditional guitar speaker will give you the familiar and fairly easy to set up "amp in the room tone". This does limit possibilities, because any sound you will create will be colored by the character of the guitar speaker. When using a traditional cabinet, the preset doesn't need to contain a Cabinet model. If it does, disable it or disable Cabinet Modeling in the processor's setup menu.
To feed the guitar speaker, a hardware power amp is required.
This can be a guitar-oriented power amp, head or combo, which will add it own coloring to the sound and decreases the possible tonal variations. This usually sounds best with Power Amp Modeling disabled in the processor's setup menus.
More popular is a so-called "neutral" power amp, which neutrally amplifies the incoming signal into the guitar cabinet. This relies on the virtual power amp, so keep Power Amp Modeling enabled in the setup menu.
Alternatively, you can opt for FRFR sound reproduction and amplification: Full Range Flat Response. This requires a FRFR speaker and an external or built-in neutral power amp. Studio monitors are FRFR by nature, as well as some monitor wedges and cabs, high-quality PA-systems, and headphones.
FRFR systems and direct recording require Cabinet Modeling because the signal doesn't go through a traditional guitar cab. The Axe-Fx and AX8 have many built-in cabinet models. They also allow loading additional cabs from disk, known as Impulse Responses (IRs).
Important: when using an FRFR sound system with cabinet modeling, you're listening to the sound of a miked speaker. That's a different tone than that of a guitar speaker cabinet. A virtual cab (almost always) represents the sound of a speaker that was captured using one or more microphones placed very close to the speaker (referred to as "nearfield" or "close-miking"). The sound of a guitar speaker at a certain distance is referred to as "far-field". Because of the close proximity of the recording mic to the speaker, the FRFR sound has more highs and lows, and has the characteristics of the microphone baked in. It can take a while to get accustomed to the FRFR sound, but realize it's the same tone you hear at a concert or when listening to recorded music.
Cutting through the mix
Lots of players who start using a modeler and take it to rehearsals and gigs, using FRFR amplification, find it difficult to make the sound of the guitar cut through the mix. Even turning up volume doesn't always help. This is caused by two things:
- close-miked sound
- Fletcher-Munson curve
- About close-miked sound
Already explained is that the FRFR sound is the sound of a close-miked speaker, which usually has more top and bottom end than a regular guitar cabinet. The fact that its spectrum is very broad, makes it harder to get noticed. The electric guitar is a mid-heavy instrument.
- About the Fletcher-Munson curve
The Fletcher-Munson curve is the scientific name for the fact that human ears perceive sound at low volume levels differently than at higher levels.
When tweaking tone at low volume levels, a player often turns up treble and bass. This is what the "Loudness" switch on older home stereo systems did. But when the volume is turned up, those high and low frequencies are the cause of harsh and boomy tones. In the highs the guitar now needs to compete with cymbals, and will lose. In the lows the guitar now needs to compete with the bass guitar, and will lose.
The solution to this: simnply don't dial in too much top and bottom end. Always dial in your live guitar tones at gig levels. And remember that the guitar is a "mid" instrument, so focus on the midrange.
Input and output clipping
Clipping means that a signal exceeds the limits. While analog clipping may sometimes be desirable, digital clipping is always nasty and something that you'll want to avoid.
Clipping can occur at various stages.
- Input clipping
Input clipping means that the incoming signal is too hot.
It's okay for the Input LED to "tickle" the red. If it happens all the time, adjust Input Level / Input Pad in the setup menu. This control is NOT a gain control! It controls the signal-to-noise ratio and does NOT affect signal level, amp gain or tone.
- Output clipping
The Output LED indicates that the signal level in the effects chain is too hot for the digital-to-analog converter at the end. Adjusting the Input Level will not solve this. Decrease the digital level somewhere in the chain, preferably using Level in the Amp block, or in the Output block.
The sheer number of parameters and possibilities with amplifier and cabinet modeling can easily dazzle and confuse. It's handy to fall back on a reference tone.
The Band-Commander (clean tone) and Friedman BE (dirty tone) amp models, both at completely default settings, provide great reference tones. Combine with cab model #103 at default settings.