Simulation of vacuum-tube amplifiers

Vacuum tube amplifiers are said to add ‘‘warmth’’ to an audio signal. They are used for subtle signal modifications as well as soft sounding distortions. But since most signal processing for musical recordings is performed in the digital domain, algorithms for a digital simulation of the desired effects produced by tube amplifiers would be useful. In the work presented here two approaches are followed. The first is based on the simulation of the characteristic transfer curves (waveshaping) combined with a frequency response correction. In the second, more complex one, the complete electronic circuit is simulated using an analog behavioral model of the vacuum tube. The output signals of the simulations are compared to the output of a real vacuum tube preamplifier analytically as well as within listening tests. The computational cost for a real-time implementation of the different algorithms is set into relation to the simulation results.