Swamp XT Pro is a free VST instrument synthesizer features ‘Timbre-modulation’. It is processing each oscillator’s waveform in a very unique way in changing i.e enriching or limiting the harmonic spectrum making the sound fatter, wider or narrower even til near dissolving it to some way distorted noise depending on the input wave.
While the prior Swamp had an oscillator routing to balance it’s output between normal i.e. direct signal and timbre modulated signal which each could be balanced to go to direct out or to filter this has been straightened in Swamp XT: direct und timbre modulated signal can be balance mixed to one signal and the output of both oscillators can be balance mixed too. While the direct and filtered signal can be balanced at the amplifier stage of Swamp XT.
All in all Swamp delivers a wide variety of sounds even to some really strange and weird ones if you want these.