P3D Re: What the *&^%$# ?

["Gregory J. Wageman" <gjw@xxxxxxxxxx>]

Mark writes:

>Some common audio terms like separation, mixing, frequency response,
>feedback, delay cannot relate to photography.

Not true.  Some have exact equivalents.

"Separation", actually more correctly "channel separation" refers to the
degree of crosstalk between left and right stereo channels.  Because audio
systems often involved lots of engineering compromises, what was intended
for the left or right channel only didn't necessarily stay there.  Phonograph
pickups (remember those?) have particularly poor channel separation.  Modern
digital playback systems like CD have effectively zero crosstalk, because
the channel information is recorded and decoded discretely.

Crosstalk is also effectively zero for our typical stereo cameras and slide
viewers, which use dual optical paths.  However, crosstalk is a frequent
problem with red/blue (or cyan) anaglyphs when the filters don't match the
dyes used.  "Ghosting" (incomplete extinction) in polarized projection is
also crosstalk.  We don't typically use the term "separation" to describe
it, but it is completely analogous.

Frequency response is perfectly applicable in the photographic realm.
Remember that light is a wave, and different emulsions respond differently
(have different sensitivities) to different wavelengths of light, as do
our own eyes (highly sensitive to green, less so to red, even less so to
blue).  When we talk about some films appearing "warmer" than others, this
is evidence of increased response to lower frequencies of light (oranges
and reds), just like we talk about tube amplifiers sounding "warmer" than
transistors due to differences in generated harmonics (even-order vs. odd).

Feedback and delay are time-domain phenomena, and so long as we're talking
about still photography, don't apply.  However, there is such a thing as
video feedback (point your stereo camcorder at the television while monitoring
its output for a real-life example).  I think the delay you're referring
to is probably an effect, which is actually a delay combined with attenuation
and feedback.  Such effects are possible in the video realm, but are rarely
used except perhaps in music videos.

	-Greg (gjw@xxxxxxxxxx)


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