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The MAIZ
When you were a kid in high school you should have learned
that nothing can travel faster than the speed of light. Nothing,
that is, other than a police vehicle which is about to give
you a ticket, the rumour that you’ve broken up someone
else’s marriage, the person who sniped that must-have-widget
from right under you on eBay, or the piece of gold that
just fell out of your tooth. Gold teeth break another law of
physics: despite being more dense than everything else,
they dissolve into invisibility when placed in a sink. Somewhere
in the greater sewage system, there is enough gold to
buy the sewage system.
Light travels at light-speed, which is kind of fast. Electricity
travels at almost the speed of light in a wire, and the
“almost” is of no practical impact if the electricity is carrying
audio. But sound travels at the speed of sound outside
a wire and that’s also important. If you put on a pair of
headphones and talk to yourself through a microphone,
you hear two things: sound travelling to headphones at the
speed of light, and sound travelling through your head at the
speed of sound. As long as those two sounds arrive at the
ears in reasonable alignment, all is sweet. In the scheme of
analogue everything, it’s hard to misalign those two sounds
even though your bones don’t conduct at the speed of light.
Mostly this works because bones conduct sound quickly
enough, which is true. Even for that performer on your
gig who has an incredibly big head. “Quickly enough” is the
important bit.
Speed of sound becomes a different problem when you
move to digits. Digital processing always adds delay to a signal.
That’s because it takes time to do maths, just like in real
life, and because most digital processes add a bit of buffering
to ensure that the electronics gets everything right before
the signal is shipped off to the next process. Delay, delay,
delay, some of it decidedly nasty. It doesn’t take too many
processes before the delay starts to add up in ways that
aren’t good. Go back to the experiment of listening to your
voice on headphones. As you add more and more delay to
the headphones, the voice in your ears gets out of step with
the voice in your head. Despite several squillion years of
evolution, no Darwinian effect has yet had time to teach our
brains how to deal with hearing ourselves through a digital
delay. That means the brain has no coping mechanism, just
some threshold at which it becomes important.
Above that threshold it works a bit like this. The first
thing you notice is something wrong, but maybe you don’t
know quite what. A bit more delay and you start to hear
comb-filtering effects as the brain adds the two signals
together. your head becomes a flanger. It’s weird, but
tolerable if you absolutely have no alternative, and you can
learn to deal with it, maybe. A bit more delay and you start
to hear a semi-distinct echo. At this point you might want
to go and look up “Haas Effect”, and discover how slight
delay (and even lots of delay) has been used to great effect
in control rooms and Dolby surround. As the delay knob
is turned up to extreme, you get beyond Haas Effect and
move into being unable to deal with the delay at all. Feed
100mS of delay into someone’s headphones and watch them
squirm.
We need to understand the impact of delay. All digital
consoles introduce delay; it’s unavoidable and it comes with
the territory. Design engineers go to very short lengths to
keep those delays to something small in the hope that the
delay won’t be noticeable or troublesome. Most manufacturers
and all salespeople will tell you that anything less
than three to four milliseconds is don’t-worry or maybe
don’t-care. True if you’re listening to yourself on foldback
speakers, if you’re listening front of house, or even if you’re
listening to monitors in an anechoic chamber. But as soon
as you start listening to yourself on headphones it’s vitally
important. Where would that be? In-ear monitors, for one.
Talent IFB. All radio presenters.
I’m sort of comfortable with the concept that most people
don’t react to a delay of less than three milliseconds. But
here’s the thing: go and try to find anyone who can tell you
in cold hard researched terms what you REALLy need to
know, which is whether a couple of milliseconds of delay is
important to the artist who pays your wage. There’s really
only one person who can tell you that, and it’s the artist.
And just like in the early days of transistors, just because the
test instruments tell you that there’s no distortion doesn’t
mean that nobody can hear the effect, or that it isn’t off-putting,
or that it isn’t important. I get tired of salespeople
who say it isn’t important, because they aren’t the end-user,
and they aren’t the people who feel the pain.
The new world is one of big shiny digital consoles that
have so much to offer in terms of everything operational,
and where electrical measurements become insane: no noise,
infinite frequency response, unmeasurable distortion, and
they never go out of whack or need tweaking. But they do
have delay, and as you feed one console into another, and
loop through and back and around a couple of times, and
in and out of outboards, and… well, those delays add and
sooner or later you need to expect that someone will notice.
Be aware, be very aware, and ignore at your peril. Oh, and
check that you have a few short-path mix-minus feeds available
for the talent. Just in case.