The "TIA-1A Hardware Manual" [1] states: "This circuit contains a nine bit shift counter which may be controlled by the output code from a four bit audio control register (AUDC), and is clocked by the frequency select circuit. The control register can be loaded by the micro- processor at any time, and selects different shift counter feedback taps and count lengths to produce a variety of noise and tone qualities."

[1] https://www.atariarchives.org/dev/tia/

There is an "about 30KHz" base frequency, so "div 15" suggests a 2KHz waveform; "4 bit poly" and "5 bit poly" are probably two of the "feedback taps", "and" a logical multiplication of these signals. But this is just my interpretation.

[Edit] For technical details see: https://alienbill.com/2600/cookbook/music/stolberg.txt