[Frank Stearns]

"Peter Larsen" writes:

Don Pearce wrote:

I have two ways.

The first way is to stand where the spot-miked instrumentalist will be
and clap my hands. Alignment is simple.

Should'a done, but plain forgot.

The second is to do the job properly and measure the paths to the two
mikes. The speed of sound (just over 340 m/sec) then gives the delay
needed on the spot mike.

I kinda do want a laser measuring device for that .... just never made it to
the top of the shopping list. Also at an AES meeting at DR (Danish State
Radio) they explained that they used the laser measured distance X 0.66,
that was what sounded right. To me that gives audible doubling ....


With all respect to those who want to simply measure to derive the delay factor (via
a tape measure, spikes on the waveforms, whatever), you're being a wee bit
simplistic.

And I include my earlier self in that group.

I used to all the time use and promote the use of a dog training clicker (makes a
nice visual on the waveforms; way better than a clap), but then reality eventually
caught up with me. w


Here are the problems with simple measurment:

- with a single, small point-source instrument, theoretically your measurements will
work, ASSUMING that the point source, spot, and main pair are in a line. (Somewhere
it was noted that DGG made sure that instruments, spots, and mains were each on a
line.)

But if they are not in a line (for any number of practical reasons), **and the
player or singer moves** the alignment veers as the player moves; then you have
variable comb filtering that can sound pretty wonky. If things are in a line, this
problem is mitigated, but things still might not be ideal.

- with a wider source that you're spotting, say a wind section, choral section, even
a large piano, you might clap or click at just one place, but what about a few feet
to the left or right? Your path distances change, as must your delay -- but for
which location?

And if the spot and mains are not in a line, and your spotted source has depth, now
you have compromised settings forward and back as well.

- I too use 50 cm AB... So, which main pair mic should you align to? If to a phantom
point between the AB microphones, the alignment for both are wrong (and audible) and
becomes even more wrong (for at least one of the microphones) as the point source is
farther left or right.

Visualize those vectors in 3D; note the problems.


This is why I've switched to aligning by ear. Sometimes the alignment is close to
what distance measurements might suggest, sometimes more, sometimes less. Every now
and then you get a serendipity of comb filtering that actually helps the overall
tone (though rare).

More often the delay will be a bit more than what distance might suggest, but less
than Haas. You're out of the worst potential comb filtering whether the player moves
or not. The more-than-needed added delay can "outline" the spotted instrument so
that you can actually use a bit less in the mix and still get the highlight you
want. (And using a bit less is good, because you further reduce audibility of
residual problems.)

My $0.02. As always, YMMV.

Frank
Mobile Audio
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