Advice please on basic additive with comfortable GUI and fine tweaking of partials

[VariKusBrainZ]

Synclavier is really pretty awesome. Getting it as a bundle with all the other instruments is a nice bonus!

+1

And

+1 MPowersynth

[egbert101]

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[VariKusBrainZ]

AIR Loom is also pretty cool and can be had for peanuts quite often

$50 at Sweetwater
£30 from Thomann

[aMUSEd]

Loom is good but doesn't offer the partial by partial type addictive editing the OP wanted (however it does have a higher quality sound than most additives imho)

[xx JPRacer xx]

Thorn by Dmitry Sches (really nice guy and responsive dev) is a superb spectral synth and you can edit the partials of the waveform and do morphing. Special intro price until the end of year. Highly recommended! (and you can also check this long thread here: http://www.kvraudio.com/forum/viewtopic ... 1&t=493006)