[sdiy] Long LFSRs (Was Psych Tone)

[Donald Tillman]

> On Jan 6, 2019, at 2:42 AM, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
> 
> 2 taps. Feedback from 126 and 127 as per recommended polynomials for maximum length sequences stated in this document:
> 
> http://www.xilinx.com/support/documentation/application_notes/xapp210.pdf

Ah...  

For any given LFSR length, there are one, or more, or a lot more, choices for feedback taps for a maximum length sequence.

For a reasonable random generator you want to choose a set of taps that are distributed along the length, with one pretty close up front.

The setup you have there with two taps at the end effectively creates a transmission line, and that's what you're hearing.

  -- Don
--
Donald Tillman, Palo Alto, California
http://www.till.com