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Quote </td></tr><tr><td id="QUOTE">Yes, but what makes a recording truly digital in the first place? Just the fact that there's no physical contact of any kind? Is that what it's all about?</td></tr></table>
Hoo boy. We have to talk about fundamentals here: what do "digital and "analog" mean?
A digital recording -- digital electronics of any kind -- is based on numbers, usually binary (1 and 0). A CD is made up of microscopic pits and flats corresponding to the 1s and 0s. In turn, a digital master tape is simply encoded with 1s and 0s. In both cases, these correspond to on and off switches. Your CD player reads the sequence of 1s and 0s/on and off pulses and, using some seriously gnarly math (the Nyquist-Shannon theorem), reconstructs the original audio waveform with great precision. I'm a math idiot so someone else will have to explain that.
Analog recordings -- or analog electronics of any kind -- are not based on numbers. If digital is basically a bunch of switches turning on and off, analog is based on continuously variable but constant signals. Analog is always "on", but it varies smoothly and constantly. Think of it as a volume control (or other kind of potentiometer) being turned up and down. The wiggles in a record groove are physical analogs of the sound waves that traveled thru the air to the microphone in the first place. Those wiggles get turned into a constantly fluctuating voltage -- always on, but varying -- by the phono cartridge and other analog components in your audio gear. The voltage fluctuations are analogs ("equivalents"
of the original sound. And those wiggles are themselves analogs of the voltage fluctuations produced by the microphone, the mic preamp, mixer, tape recorder, and so on throughout the recording /mixing process.
When you think about it, an old-fashioned music box is a sort of digital device, albeit crude. It has holes in a disk that engage metal tines that make that tinkly music. There's either a hole or there isn't. It goes "plink" or it doesn't; it's either "on" or "off". What it lacks (among other things) is the math to reconstruct the comples audio waveforms that characterise the sound of singers and orchestras. So, yes, there can be physical contact. Same with Morse code. Or a Jacquard fabric loom (look it up -- the Jacquard loom is considered a precursor to our digital computers!).
To sum up: digital electronics are based on discrete, numerical processes. Analog is based on continuously and infinitely variable signals.
Basically, the trouble with analog is that at every step of the way -- every time a signal is converted into another analog of the previous signal -- there are inevitable losses and distortions. And there are lots of steps in the process between the recording microphone and the finished LP or CD. By definintion, an analog of something isn't an exact copy of the original, but something that is "like" the original but in another form. "Like" is not the same as "exact".
In contrast, the 1's and 0's of digital stay the same at every step, so the CD is much closer to the original master tape. There are only two places to incur distortions and loss: when the analog signal of the microphone is transmitted to the digital recorder, and then when your DAC converts the digital signal back to analog (leaving aside your amp and speakers for the moment).
Once upon a time, there were even analog computers!
(If you've made it all the way thru and are saying to yourself "I'm sorry I asked", I don't blame you!)</font>