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Looper's Delight
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> I'm no programmer but it seems like doing sync and
> feedback is very hard. Even the EDP looses it's sync when in
> overdub with a feedback of <100, right?
It's a slow day and I haven't bored the list in awhile, so here goes...
The general problem is synchronizing while doing any type of
recording. For those old enough to remember tape decks, think of it
this way. You have a drummer and a tape recorder. The tape contains
a pre-recorded song at 120 BPM. You tell the drummer to start playing
at 120 BPM and at exactly the same time start the tape, only the
drummer can't hear the tape. Eventually the tape machine and the
drummer will drift out of sync because they are both following their
own internal "clocks". Your job as a recording engineer is to keep
the song playing on the tape machine in sync with the drummer.
The drummer speeds up slightly, now it sounds like the tape is
lagging. You have two choices. Through some technology miracle that
was never invented you can stop the tape machine, fast forward it
slightly so that it catches up to where the drummer is, then restart
it, all in about a millisecond so the listener can't hear the
adjustment. Or if you have variable speed control on the tape machine
you can speed it up very slightly until you've caught up with the
drummer, then return it to normal speed.
Call the first technique "instant skip" and the second "variable speed".
Now let's say that this was a multi-track tape deck and you also had
an accordion recording on another track while the first track is
playing with the drummer. The engineer decides to make a sync
adjustment. Using the instant skip method, what will happen is that a
short gap of silence will be inserted into the accordion track.
This will cause an unpleasant artifact when you play it back, which was
already unpleasant enough because of the accordion.
The variable speed method is better. Here, the tape keeps rolling, it
just speeds up slightly so the accordion performance will be recorded
seamlessly. If you listen very closely on playback, you may notice
that the accordion sounds very slightly flat during this adjustment
period. This is because the tape is being played back at constant
speed while it was recorded at a higher speed in spots. If you had
some fancy outboard pitch shifting gear and inhuman precision you
could apply a bit of upward pitch shift to the accordion during
those times where the tape is playing faster to compensate.
Now warp into the modern era of digital loopers. The EDP and most
other loopers that I'm aware of that can synchronize with an external
clock use the instant skip method. If you were overdubbing when the
skip happens, it would produce an audible "bump" when the next loop
plays. Some loopers that use the instant skip method therefore
disable synchronization while recording is enabled, the thought being
that it is more important to capture the overdub accurately than stay
in sync.
I've never used a Repeater but from what I've read it appears to use
the variable speed method. I don't know if it does a corresponding
inverse pitch shift to compensate for the speed change, but I would
expect it does.
So, going back to the original question: is sync with feedback hard?
It depends on how they've implemented feedback. If feedback is
continuously applied as on the EDP then you can "play" feedback by
twisting the knob in a musical way. Let's say you were sweeping
feedback up to create a swell. If we did a sync jump forward in the
middle of this sweep, there could be a brief plateau in the feedback
curve that didn't match what you played. I haven't explored how
loopers handle this but I'm guessing most ignore it and do not disable
sync while feedback is being manipulated. This is arguably fine
because the distortion you may get is far less noticeable than what
you would have when overdubbing.
Anyone still awake?
Jeff