Pairing W2821B Led's into individual Sudo Pixels

[Grumpy_Mike]

@chainmaker

Erm The How to get the best out of this forum General Section - "partly because we feel that if you want our help you should provide everything we need on this site not expect us to go hunting elsewhere for it."

Hence I was reticent to provide a link to the original project

Are you an native English speaker? I ask because those words from the guide do not lead to the conclusion you reached from them. They mean exactly the opposite of your conclusion.
When it says :-

you should provide everything we need on this site not expect us to go hunting elsewhere for it.

It means that, for example, you say I am following the tutorial by G. I. Joe, then you should supply a link to that tutorial, and not expect us to search for that tutorial. Mainly because he might have written many on the subject and we don't know which one you are following, but also this takes time and that name might not be unique.

@chainmaker

What is generating the potential noise

The signals are fast with square edges, therefore this contains lots of high frequencies. This means that the wiring has to be considered as a Transmission Line. When a signal edge is sent along a wire and it reaches the far end of that wire, unless the impedance of the termination, matches exactly the impedance of the transmission line, that edge will be reflected back, and will interfere ( as in constructive / destructive interference ) with the next signal coming along. It will indeed reflect off the the start of the wire again. This effect is used in time domain reflectometry.
The resistor is there to absorb these reflections, the longer the signal wire the more reflections you get, which is why it is not a problem for short distances, but is a problem for the first LED in a strip which is normally some distance away from the source.

Here is a picture of an oscilloscope trace of using / not using a series resistor with a WS2812 LED.

@chainmaker

why does it not appear to be a factor on every single strand example I have seen using a single resistor?

Three reasons

1. When driving a strip you only need to consider the wire ( transmission line ) between the Arduino and the strip, for all the LEDs on the strip the connection distance is too small to matter.

2. I have seen projects that (correctly) do this when chaining strips together especially when the strips are some distance apart. A typical project like this might be for Christmas lights covering a house.

3. There is a lot of crap tutorials and projects on the net written by people who don't know what they are doing and think because what they have thrown together is fine, because "it works". They don't even own an oscilloscope so they don't know anything is wrong, or how close it is to breaking, or attribute problems to other things like power supply issues.

It is less critical at which end of the wire the resistor is put because it acts like an impedance matcher for the whole line.