I'm trying to do something psychedelic with guitars — a bit like the song 'NY' by Doves — and I think the same effect was previously used on 'Voodoo Child (Slight Return)' by Jimi Hendrix. I have tried messing around with the Leslie and delay effects that you get with Logic 9, but have not even come close. What is that effect?
Via SOS web site
SOS Editor In Chief Paul White replies: The sound on that record was almost certainly produced by flanging the whole track. You can get close using a flanger plug‑in, though the original effect was created by running two tape recorders carrying copies of the same tape, then adjusting the speed of one of them so that one machine overtakes first of all, then falls behind the other. As the machines weren't perfectly in sync, the small delays caused phase cancellation of specific frequencies, and these varied as the relative timing between the two delays varied. That's what produces the familiar 'whooshing' sound.
The tape speed was adjusted either by using the varispeed control on one machine, or by slowing one, then the other machine slightly, by dragging the hand on the supply tape-spool flange. The most impressive effect occurred when one machine caught up with, then overtook the other. As you can imagine, the process was a bit hit‑and‑miss, as you had to line up both machines so that they'd start at the same time, but it certainly produced a trippy sound.
Flanger plug‑ins can process both mono and stereo mixes, but most tend to operate from an LFO and so can sound rather too regular. But if you automate the speed and depth controls to create a pseudo‑random effect, it can add an authentic feel. Most flanger plug‑ins are also limited in the minimum delay time they can apply, so can't quite recreate the 'through zero' effect of tape where one machine passes the other, though some of the more advanced plug‑ins use an additional delay in one side of the signal path to fake this effect. .