The Real Reason Why The Pros Like Amp Sims (and you should too)

At some point in any review of any guitar amp, no matter if it’s a 1 watt Marshall or a 100 watt Fender, the reviewer will say something along the lines of “this thing can get real loud”. Every amplifier, every review. Maybe there’s a reason?

There is. Guitar amps have Celestion speakers, or something very similar. These have sensitivities around 100 dB / watt at one metre for a 1kHz tone.(1) That’s eight times louder than you play your stereo just before someone else in the house asks you to turn it down.

At one watt. Never mind five, ten, or twenty-eight watts.

It’s not the guitar that’s loud, it’s the speakers.

What everyone wants is a) a decent amount of sound with a “clean” tone, followed by b) that magical edge-of-breakup as the valves start to run out of headroom and clip the output waveform.

However, in a conventional valve amp, achieving the first means that the second is only available at ear-damaging sound levels. Conversely, getting edge of break-up at practice volumes almost ensures that the clean sound isn’t that consistent.

So the world is full of guitar enthusiasts, and indeed professionals, with wonderful valve amps that are forever on 2 and never reach break-up, which is daft, because the point is the edge-of-breakup tone.(2)

Except…. I mean, I can play Band of Gypsies on my hi-fi and hear that tasty Hendrix tone at sensible volumes - granted that the excitement from higher volumes is missing. What’s going on?

The edge-of-breakout tone needs the valves in the power amp to be driven hard, which produces a powerful output. Is there a way of sending the waveform to the speaker without sending all the power? It’s usually called attenuation and can be done in a number of ways, and usually, the cheaper the way, the more that lovely hard crunch turns into an irritating fizz.

At least for analogue methods. Using a decent ADC -> DSP -> DAC sequence may be better, but this starts to turn the amplifier into a hi-fi amplifier, with consequent costs and development programs that only the larger companies can even consider. Guitar makers are old-school electrical engineers unused to the delicate touches required to keep ADC / DAC chips running well, and DSP algorithms are still “secret sauce” even in hi-fi.

The result is that we have amp-simulation software, developed by computer-centric companies. Kemper, Helix, and others.

The idea is to record an amp doing its thing as its designers intended, and then throw some kind of wavelet analysis at the input and the output.(3) This provides a description of the change from before-to-after which can be summarised by a mathematical model, which can be turned into fast algorithms run on multi-core chips in specialised computers disguised as multi-button pedals. The required tone is now available independently of volume levels.

It’s not perfect (though neither is the manufacture of valve amps) but it’s a process that can be iterated for improvement.

So we have a gadget with an ADC at one end, a bunch of algorithms running on fancy chips in the middle, and then a DAC to provide an analogue signal to an analogue amp, or a USB connection to a laptop running a DAW.

And not a speaker to be seen, let alone heard at intolerable volumes. This is why the professionals jumped at using the computerised stuff, despite already having a studio with selection of valve amps and speakers. It was much quieter and much less temperamental (just listen to engineers talk, for instance, about how mic placement changes from speaker cab to speaker cab, even when both cabs are the same make and model).

This also changes the role of the amp / speaker for live listening. We’re not looking for it to provide the tone - clean or beak-up - but to be as neutral or flat as a hi-fi system.(4) Right now the guitar business doesn’t have too many of this so-called FRFR (full-range, flat-response) kit, and what it does have is often described by the familiar phrase “this thing can get real loud”.

Which really does bring us back full-circle.

(As you can tell, getting a Helix LT is now my current first step on the gear-upgrade path.)


(1) Hi-fi speakers are often in the 83 - 90dB / watt range. Which is somewhere between half and a third as loud. 

(2) Unless you’re Tim Pierce and have your speakers in a soundproofed basement, played as loud as you need with only microphones to hear it. 

(3) It probably is wavelet analysis, but it might be something else with the same result. 

(4) Yes, I know. But in comparison to guitar amps, decent hi-fi’s are pretty neutral.