By virtue of their electrical properties, tubes generate a special waveform when they're saturated, which is why tube engineering has tremendous tonal advantages over solid state or DSP solutions, particularly for crunch and lead sounds. Tubes enter the saturation zone gradually or softly, which lends tube-driven tone its trademark yet totally unique character.
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3. An equalizer would be useful to change the tone from ur amp slightly by changing the bass and treble etc. It would be used for the same reason live probably. Perhaps if the PA system was crap you could regain your tone using an equalizer.
