On Dec 22, 2006, at 10:19 PM, Dennis Bathory-Kitsz wrote:
At 09:49 PM 12/22/2006 -0500, Williams, Jim wrote:
What about chorus, though? Any suggestions on that? I'll experiment,
of course, but I'm wondering if you have a principle on that?
I've never liked it and don't use it. Some people use it
effectively, but I
just don't. My attempts come out sounding like a robot ensemble.
I suppose you know how chorus is supposed to work? If you do (as I
imagine) then just sit back while I explain it for the benefit of the
others.
The idea is to make it sound as if more than one instrument is
playing when only one is. Since there are NOT two different flutes
playing, but only one, then the effect has to be faked. The sound is
sampled and quickly played back slightly pitch shifted and only a few
milliseconds later (kind of like reverb, in fact, but reverb is not
pitch shifted and is much more complex and gets the copies filtered
because of diffusion and absorption and other things) so that you get
the impression of two instruments playing the same thing almost at
exactly the same time. Add a few copies of this, and change the delay
time and pitch difference slowly so that the phase relationship
changes, and you have a cheap chorus. The copies are panned around in
the stereo field and have their volumes reduced, too, to add sonic
interest. A Leslie rotary speaker is a kind of a chorus effect,
depending on the Doppler effect as well to get the pitch element
involved.
If there are only two sounds, and the timing between them changes
regularly, this a flange effect (named because engineers would play
back two copies of the same tape at the same time, slowing them down
alternately by pushing their thumb on the flange of the tape reel.
Now this is done electronically.)
Obviously, this DOESN'T do a great job of giving the impression of a
multi-instrument unison, but the effect has gained popularity because
it does sound distinctive and it does thicken the sound, though not
exactly like a unison would. My favourite way of thickening a unison
is the way GPO does it; by having DIFFERENT players playing the same
note. The differences in timbre between two different players is
enough to give a rich unison sound.
One of the artifacts that shows up in cheap chorus effects is comb
filtering. This is a little hard to explain in text (I explain it on
the blackboard with visuals at school), but the sound can be a little
like a robot when it is taken to an extreme. Basically it means that
if two waveform peaks coincide, then that frequency is emphasized,
while if a peak and a valley coincide, then the frequency is
dampened. Two copies of the same sound at slightly different pitches
will have alternating bands of emphasized and de-emphasized
frequencies, as if your graphic EQ had the sliders set alternately
all the way up and all the way down, like a comb. Flanging (see
above) depends on comb filtering, and also on having the "comb" move
around, but in acoustic music it sounds unnatural.
Summary - chorus can sound great as an electronic effect, but it
doesn't sound natural on acoustic instruments.
Christopher
PS - true studio anecdote about comb filtering:
I had hired a terrific trumpet player to dub two trumpet parts on one
of my studio projects. He was so incredibly consistent from one take
to another that there were comb filtering problems in the unison
sections, sounding metallic and unnatural. We could have addressed
this in many different ways (different mic, different room damping,
different positioning), but the easiest way was for him to take his
other (larger bore) trumpet to play the second trumpet part. Just the
change of bore (and make, from Bach to Schilke) was enough to make
the second trumpet part different enough in timbre to eliminate the
comb filtering.
Second true studio anecdote:
Vocal overdubs on a pop tune, the same woman (a wonderful singer) was
recording all the parts, sometimes several passes on each part. It
was starting to sound weirdly unnatural, like that moment in the
Matrix movie when suddenly there are hundreds of copies of Smith
inhabiting the universe. She knew exactly what to do, though. She
sang second, third, and fourth passes with a different accent! Not
enough to screw up the diction, but enough to change her natural
formants and eliminate the "clone" effect. We were peeing our pants
laughing over the individual takes, but mixed all together they were
incredibly rich and sounded like a fantastic women's choir. I watched
her and sometimes she was pursing her lips while she sang, sometimes
she smiled, sometimes she closed one nostril with a finger, and
sometimes she put her hand up beside her mouth. It was a big learning
experience for me.
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