2015-11-30 22.28.44

Scooping the Mids

By Scot, December 1, 2015

Most guitar players know how to turn the knobs to get the frequency balance they are looking for from their amps. But I doubt that they really understand what is happening to the guitar signal with those little knob changes.

I was chasing down an elusive noise when i hooked my LLamaTone Phoenix MXL20, hand built guitar amp to an old oscilloscope. After a few frequency sweeps, I was interested by how the tone knob changes affected the O-scope images.  This amp has a usual Treble, Mid and Bass knobs, much like the ones found in many Marshall and Fender amps.

To show simply and clearly, I ran two sweeps from about 60Hz to about 2.5kHz is 14 seconds. The videos show the O-scope reading as the frequency rises. For the first video, I had all three knobs in a middle position. Notice how the amplitude of the signal remains relatively constant during the sweep. (I kept the sweep volume low to save my sanity (it’s tough listening to the same frequency sweep over and over…)

 

 

For this second sweep. I set the tone controls as mid scooped , or high treble and bass settings, but the mid knob turned all the way down. It’s a useful tone shape for heavier styles of guitar music. Notice in the following video the amplitude of the signal attenuates (lessens) as it approaches a mid center frequency, then increases as the range turns to treble.

 

 

I get a kick out of visual representations of everyday non-visual occurrences.