The antecedents of digital (Part 1)
David Robertson (internal link) writes:
"Later this month I'm giving a major talk about my hero Alec Reeves at the IEE. To save boring you here, details are at http://www.iee.org/events/alecreeves.cfm. (external link)"
"As part of the work for my paper for the IEE, I'm trying to get to grips with the 'antecedents' of PCM - the ideas and technologies on which Reeves may have drawn. Do any of your readers have ideas or comments? We know that sampling had been suggested by Miner and Squier, while Morse or his assistant Vail came up with what we now think of as regeneration."
"What's much less clear -- at least to me -- is whether anyone else had the idea of transmitting speech in a 'telegraph-like' way - perhaps the key feature of PCM. Some writers (including, interestingly, Reeves' boss Maurice Deloraine in When Telecoms and ITT were Young) have suggested that Page, Bourseul and Reis were attempting to do exactly that when, in their early experiments with what eventually became telephony, they sought ways to turn speech into a form suitable for transmission over the telegraph network."
"It appears to me that such attempts were doomed to failure as we know they largely were are 'digital' only in the very limited, technical sense that the telegraph was all they knew about and hence was the model they were exploring. Reeves, by contrast, came after Bell and hence was proposing to sample the by-now-existing 'analogue' signal and turning these samples into 'digital', that is, a telegraph form. This appears to me a far more subtle and more complex task. In making this suggestion, I don't want to appear to denigrate what Page et al did, but I really don't see them as part of the 'digital' story."
"What do you think ?"
Tom Farley:
"Yes, you are totally correct. The early inventors, those before Bell, were all on the wrong path, thinking they could reproduce speech in those early years by making and breaking a circuit, just like with the telegraph. They were a million miles from success, just plodding along, electricians in a field that needed people familiar with electricity and acoustics. They weren't on this path deliberately but blindly, so I would pay them little attention in a history of digital beginnings."
"To quote my own telephone history series: internal link)"
In 1861 Johann Phillip Reis completed the first non-working telephone. Tantalizingly close to reproducing speech, Reis's instrument conveyed certain sounds, poorly, but no more than that. A German physicist and school teacher, Reis's ingenuity was unquestioned. His transmitter and receiver used a cork, a knitting needle, a sausage skin, and a piece of platinum to transmit bits of music and certain other sounds. But intelligible speech could not be reproduced. The problem was simple, minute, and at the same time monumental. His telephone relied on its transmitter's diaphragm making and breaking contact with the electrical circuit, just as Bourseul suggested, and just as the telegraph worked. This approach, however, was completely wrong.
Reproducing speech practically relies on the transmitter making continuous contact with the electrical circuit. A transmitter varies the electrical current depending on how much acoustic pressure it gets. Turning the current off and on like a telegraph cannot begin to duplicate speech since speech, once flowing, is a fluctuating wave of continuous character; it is not a collection of off and on again pulses. The Reis instrument, in fact, worked only when sounds were so soft that the contact connecting the transmitter to the circuit remained unbroken. Speech may have traveled first over a Reis telephone, however, it would have done so accidentally and against every principle he thought would make it work. And although accidental discovery is the stuff of invention, Reis did not realize his mistake, did not understand the principle behind voice transmission, did not develop his instrument further, nor did he ever claim to have invented the telephone.
This page continues here ----> (internal link), with many great comments by Don Kimberlin. (internal link)