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Dave Rat Transmission: Sometimes Sound Is About Time
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How fast do sound signals travel through the various parts of the sound system? Do sound signals travel faster in analog snake cables or fiber optic cables?

Also, what about transmission through the air with wireless mics? And where do the true and relevant sources of time lag exist in a audio system?

What I find really interesting is that sound signal travels at differing speeds depending on whether it’s in the form of electricity, or sound waves in air, or via wires, or passing through various pieces of commonly used audio equipment.

Consider that in 1.2 milliseconds of time:

- Sound travels about 16 inches in air before going into a microphone or after coming out of a loudspeaker.

- But if we did rock shows under water, we would find that sound cruises about 70 inches, nearly five times faster.

- It just barely makes it from the input XLR to the output XLR of the faster popular digital consoles.

- Yet it travels about 650,000 feet (124 miles) down a regular copper wire or snake, because in copper, electric signals travel about two-thirds the speed of light.

- It travels about a million feet (186 miles) down fiber optic cable; however, it can take about 630 microseconds (over half of our 1.2 milliseconds) to be converted from analog audio to digital light (and vice versa) at each end.

- But if the analog audio signal is already digitized prior to the fiber optics system, the conversion time can be cut to about 10 microseconds.

- You could probably string together every piece of analog gear you and everyone you know have ever owned plus the entire analog inventory in the Rat Sound warehouse, and experience virtually no time lag. (Analog does not delay much at all.)

- It takes more time for sound to travel one inch from a singer’s lips to the mic than it takes for a wireless transmitter to convert sound to RF, transmit it 75 feet to a wireless receiver, and then send it through an analog console, compressors and EQ, and then convert it back to RF via an in-ear monitoring system and get it all the way to the little speakers in the singer’s ears.

As noted above, sound moves through analog gear so fast that it can be considered instantaneous for most purposes, while digital is a bit more confusing because sound makes several stops for conversion between analog and digital.

Further, once signal is inside a piece of digital gear, it can slide behind in time further as processing is added the signal path, unless the manufacturer has implemented compensating delays that lock the delay time at the maximum processing time.

What does this all mean?


Comment (1)
Posted by Wiley Ross  on  11/12/10  at  08:46 AM
Good article. If I may add one thing. It's also important to be aware of polarity when listening to your own voice on phones or in ear systems. Try reversing the polarity and you'll find one polarity produces a much more natural sound especially with all analog signal paths. The signal from the different mics and electronics will often present different polarities. Some mics for instance are wired Pin 3 high others Pin 2. Even the electronics can invert the polarity. It's very easy to tell the one that's more in phase with your bone conduction to your ears. This makes a Hugh difference clarity.
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