Amp modellers have come a long way since the early days of the Tech 21 SansAmp but the basic idea remains the same. Circumvent the need for carrying around multiple amplifiers and effects by utilising Digital Signal Processing to emulate the sound you need. To understand how the best amp modellers work, first, we need to understand how sound works.
Soundwaves are a physical phenomenon caused by vibrations travelling through the air, water, or even solid objects. Put your chin on your guitar and play a chord and you’ll see what we mean. These soundwaves are all totally unique from one another, with a rate, frequency, and depth that defines how our ears interpret them.
DSP could have an article on its own, but the basic principle is as follows. First of all your soundwave, in this instance, an amplifier is recorded via a microphone. Using an Audio Digital Conversion (ADC) chip, your signal is turned into 1s and 0s that a computer can understand. This signal is then transferred to the Digital Signal Processor itself, typically some form of computer processing chip whereby the signal can be stored, edited, or transferred. Going the other way the signal then passes through a Digital Audio Conversion (DAC) chip to convert it from 1s and 0s back into a soundwave before being passed to your speakers and back out to your ears.
As ADC, DSP, and DAC chips get more powerful, they’re thus better able to accurately recreate the sounds we feed into them. This means eventually the technology will become so good that it will be nigh on impossible for humans to determine the difference between the two.