Distortion vs Distortion

February 1, 2011

gpnp_eguitFig_1_InputMeterFig. 1: The input meter for Phonic’s Firefly 808 Universal interface shows that the left-most guitar input is safely avoiding the red zone.


gpnp_eguitFig_2_ReValverFig. 3: Guitar Rig has a Learn function for optimizing internal amp levels.


ONE REASON GUITARISTS CAN GET bad amp-sim tone is from not realizing there’s the potential for two types of distortion within modules like amp 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.

Here’s the deal: With analog technology, if you overload an amp input you just get more distortion. Because it’s that sweet analog distortion, it sounds fine—just more distorted. But if you overload a digital amp’s input, remember that digital technology has a fixed, unforgiving amount of headroom. If you don’t exceed that headroom, the amp sim will sound as the designers intended. But if your signal crosses that threshold, the result is 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.

To avoid digital distortion, optimize levels as you work your way from input to output. First, make sure the guitar isn’t overloading your audio interface, which will probably have a small mixer application with metering. 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 the like might change levels. You can always increase the gain at the sim’s input.

Your sim will likely have an input meter and level control. Adjust this so that the signal never hits the red. Going one step further, Peavey’s ReValver includes an input “Learn” function (Fig. 2). Click on Learn, then play your guitar with maximum force. Learn analyzes your signal, then automatically sets levels so that the peaks of your playing don’t exceed the available input headroom. Beautiful.

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’s AmpliTube, you’ll find a meter—adjust the module’s volume control so there’s no overload.

gpnp_eguitFig_3_GuitarRigFig. 2: ReValver’s Learn function automatically prevents the input and/or output from being overloaded.


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 that matches levels among patches, but also prevents distortion. ReValver offers an additional output Learn function.

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.

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