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.
View post (Rolling Technique In Sweep Picking)
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using the one finger to roll over the string is the best way. It is hard but is the most efficient. Best to stick to one technique and not keep changing otherwise you wont improve on your sweeping ;)
