Amp Sim Analog Distortion Versus Digital Distortion

Posted on by craiganderton

Amp sims can have good distortion, and bad distortion..here’s how to avoid the bad kind

Amp sims have the potential for two types of distortion within modules like amps and cabinet emulators: The good amp distortion we know and love, and the nasty digital distortion that results from not setting levels correctly inside the sim.

With analog technology, overloading an amp input just gives more of that sweet, analog distortion. But digital technology has a fixed, and unforgiving, amount of headroom. If you don’t exceed that headroom, the amp sim will sound as the designers intended. But if you overload a digital amp’s input, the result can be ugly, non-harmonic distortion. Never go “into the red” with digital audio—unless you’re scoring a Mad Max sequel, and want to conjure up visions of a post-apocalyptic society where the music totally sucks.

TRIM THE INPUT LEVEL PROPERLY

To avoid digital distortion, optimize signal levels as they work their way from input to output. First, make sure the guitar isn’t overloading your audio interface, which will likely have a dedicated input and some kind of clipping indicator. Set the audio interface preamp gain so the guitar never goes into the red (Fig. 1), no matter how hard you hit the strings. Be conservative, as changing pickups or playing style might change levels. You can always increase the gain at the sim’s input.

The instruments inputs on an audio interface include clip indicators to show when the input levels are distorting.
Figure 1: This audio interface has two inputs suitable for guitar (this requires enabling the Hi-Z button, and plugging into the connector’s center). The Clip Signal indicators (outlined in orange) will light red if there’s distortion—avoid this.

TRIM THE SIM INPUT LEVEL PROPERLY

Your sim will likely have an input meter and level control (Fig. 2); adjust this so that the signal never hits the red.

Figure 2: The input level on the left is set for a good input level. The meter on the right is set too high, as shown by the red clipping indicator (circled in yellow).

TRIM LEVELS WITHIN THE AMP

Like their real-world equivalents, amp sims can be high gain devices—high enough to overload their headroom internally. This is where many guitarists take the wrong turn toward bad sound by turning up the master volume too high. The cabinets in Native Instruments’ Guitar Rig include a volume control with Learn function (Fig. 3); for sims without a Learn function, like IK Multimedia’s AmpliTube, you’ll find a meter—adjust the module’s volume control so there’s no overload.

Guitar Rig has a Learn button; if you click on it and play, the program will set an optimum level automatically.
Figure 3: Click on the Learn button, play as hard as you can, and Guitar Rig will automatically set the optimum Match Cabinet level.

CHOOSING PROPER OUTPUT LEVELS

The final stage where level matters is the output. AmpliTube has an additional level control and meter to help you keep things under control, while Guitar Rig has a special Preset Volume output module with a Learn function Fig. 4) that matches levels among patches, but also prevents distortion.

Figure 4: This additional Learn button in Guitar Rig matches output levels of your various presets, and also avoids overloading the output.

If you set gains properly through the signal chain from interface input to final output, you’ll avoid the kind of bad distortion that ruins what the good distortion brings to the party.