Just thought I'd try this one so I d/l some backing track yesterday (it had a very faint backing vocal on the left track but I sang those parts and put me left and right so 90% of that is me and all the lead vocals are me) and I don't sound just like these people but it's interesting trying this stuff.
details: processed the holy $#@#$ out of me, pitch shift by 5 semitones, eq, multiband compression, compression, auto-tune, de-essing, volume envelopes, delay, reverb.
