Zeroes, Ones and Pullman Coaches - Radio World

Zeroes, Ones and Pullman Coaches

The Transition to Digital Media Technology Mimics an Earlier Process of Time Management
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The Transition to Digital Media Technology Mimics an Earlier Process of Time Management

The concept of time zones is familiar to nearly everyone. We encounter it in a practical sense almost every time we travel or make a long-distance phone call. It is easy for us to assume that these useful covenants came with the land, and that they have always existed; but, of course, they did not. They were developed only out of necessity, and not before the period that made them so.

The natural metrics of time have always interested humans, and in the days when there wasn't much else happening during prime time to interest them, our predecessors spent a lot of time logging celestial phenomena. As a result, they became adept at understanding the cyclical processes that serve as enumerators of human experience along the time domain. Most of the cultures we classify as ancient had fairly sophisticated schemes for noting the passage of time, and for cataloguing the periodic patterns they observed in some sort of calendar.

What they did not concern themselves much with in those days were the relative, short-term variations in time between different locations on the planet. Because there were no fast methods of travel nor any instantaneous communication processes between distant locations, this wasn't an issue. Wherever you were was wherever you were, more or less; and all notations of time were adapted to that location.

As measurement of the temporal dimension became more rigorous, specific expression of time was referenced to the local maximum solar elevation, meaning that the time of day in which the sun was highest in the sky (i.e., at its northernmost location in the Northern hemisphere, or its southernmost location in the Southern hemisphere) was determined to be "local noon," and the rest of day was calculated with respect to this fairly obvious and repeatable observation.

This implied that the absolute time scale varied with longitude, and therefore the global reference to time was a continuously variable one. In other words, your noontime was a little bit earlier than that of next town to the west, and a little bit later than the next town's to the east.

Quantization

Eventually, this relativism of the geographic time domain became a problem. What is generally credited with starting the movement toward today's zonal approach to global time was an interest in scheduled travel, most notably driven by train companies. It became important to align relative and absolute times for a journey, and this was essentially an impossible exercise if every city maintained its own discrete local time reference. Discrepancies in the transmission and delivery times of telegraph messages were another motivating factor.

The movement toward a segmented time distribution was initiated in the 1880s, eventually becoming an international convention approximating an arrangement in which the globe is divided into 24, one-hour time zones. Regional and political variations have created an intricate patchwork around this concept, but the basic premise remains. Today the world's population works comfortably with a complex and tightly synchronized time distribution that reconciles local relative time with a global absolute clock referenced to a universal standard chronometer. It includes accommodation of seasonal variations with Daylight Savings Time, and an International Date Line that provides a seam delineating the start/finish line of the system.

Conceptually, this process has an interesting similarity to the transition between analog and digital media.

For example, in the analog domain, the transmission or storage of audio was accomplished by associating the instantaneous microphone output waveform with a given modulation level, in a continuously variable fashion. During reception or playback the system made its best effort at recovery of the original waveform from the demodulated signal.

In contrast, digital techniques set absolutely quantifiable steps to this process, and these representative values are what is stored or transmitted, so the accurate recovery of the original waveform is essentially assured (assuming the increments of quantization are sufficiently precise) . The one-hour increments of the time-zone system are deemed precise enough in most cases (although there are several half-hour and even one quarter-hour time zone in various parts of the world), while the Nyquist Theorem determines the requisite granularity of time steps (i.e., sampling rate) for digital media.

Synchronicity

Consider also that the global timing system relies on coordination to a standard time base, which wasn't necessary in the old "local noon" system. So too are digital media systems dependent on synchronization, so that recovered samples are reconstructed with the proper time base.

In the analog audio days, the only occasions requiring synchronization were those where multiple devices had to operate in tandem (such as two tape decks). For digital systems, even a single device operating in isolation requires synchronization so that the digital-to-analog conversion at its output operates on the same time reference as the original analog-to-digital conversion of the signal input.

Such slicing of time into parsable segments allows the technology of digital audio to exist, and also lets the trains run on time.

More about time, next time.

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