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Sunday, October 2, 2011

"That looks like line noise" "What's line noise?"

One way to know you're old: you tell someone that a certain programming language "looks like line noise", and their reply is: "line noise?" ...

So, for those who also have no idea, let's fire up the wayback machine.

For me, line noise comes from the days of using a modem. No doubt there were people suffering from it before that on hard-wired serial lines, but that's before my time. I first encountered it with my trusty Commodore 1670 modem plugged into a VIC-20. It would just turn bits into audio and vice-versa, and that meant dealing with whatever would come down the wire.

Our original phone line had this strange device in line which allowed our security system to seize it in the event it needed to dial out. The way they wired it, this meant there was a long run all the way from our demarc to the security system, into that jack (RJ31X?), and then back to the demarc. There, it met up with the original 1960s house wiring and went on to all of the inside jacks.

This particular wire ran through a hollow space just off a hallway where our house's air return was, and it punched through a wall into the hall closet where our security system's brain lived. All of this so far is no big deal. It's a typical set up all over the country. The problem is that some knucklehead stapled through the wire inside that air return.

That meant any time our A/C or heat was on, the air flow would perturb the wire, and it would wiggle against that staple, and it would generate audible noise on the line. For whatever reason, that noise tended to just be on our side of things. People on the other end never heard it while talking to us.

Back to the topic at hand, this also created line noise which I would see while connected to some BBS was entirely on my end. I might start typing out a sentence and would be presented with some funky characters in the middle. Now I had a decision to make: did that character make it to the BBS and echo back to me, in which case I should backspace over it, or was it just on my end, in which case I should ignore it?

More often than not, I wound up deleting the whole line and starting over, hoping to make it through before another burst of noise dropped some wacky character on my screen. For some reason, there were some which appeared more than others. The radical symbol up in the upper reaches of code page 437 (the so-called "high ASCII") was a particularly common offender in my house when using my PC later on.

It was a good couple of years until I picked up a modem which would do MNP or V.42/LAPM error correction. After that, those funny characters went away and life moved on. All of our CRCs and other ways of dealing with errors now make life pretty nice by comparison.

File this under "kids these days", I guess.