Thank you for the pointer to the erlang documentation. That looks like the syntax, with the : (erlang) vs. :: (elixir) difference.

Looking at that documentation inspired me to ask what elixir would construct, given the same layout as in the pattern, so I entered the following into iex. It seems that the affected bits are the least significant bits of the first byte and the most significant bits of the second byte.

Without a specification of how to place a 1 bit field and a 15-bit little endian field into two bytes, I can’t say I know how to write the elixir pattern,

I’m going to consider this as closed. (Not sure how to/if I can close a topic in this forum.) Thank you for your insights.

iex(57)> Enum.map(-16..16, &(<<0::1, &1::15-signed-little>> <> <<0>> <> <<&1::8>>))
[
  <<120, 127, 0, 240>>,
  <<120, 255, 0, 241>>,
  <<121, 127, 0, 242>>,
  <<121, 255, 0, 243>>,
  <<122, 127, 0, 244>>,
  <<122, 255, 0, 245>>,
  <<123, 127, 0, 246>>,
  <<123, 255, 0, 247>>,
  <<124, 127, 0, 248>>,
  <<124, 255, 0, 249>>,
  <<125, 127, 0, 250>>,
  <<125, 255, 0, 251>>,
  <<126, 127, 0, 252>>,
  <<126, 255, 0, 253>>,
  <<127, 127, 0, 254>>,
  <<127, 255, 0, 255>>,
  <<0, 0, 0, 0>>,
  <<0, 128, 0, 1>>,
  <<1, 0, 0, 2>>,
  <<1, 128, 0, 3>>,
  <<2, 0, 0, 4>>,
  <<2, 128, 0, 5>>,
  <<3, 0, 0, 6>>,
  <<3, 128, 0, 7>>,
  <<4, 0, 0, 8>>,
  <<4, 128, 0, 9>>,
  <<5, 0, 0, 10>>,
  <<5, 128, 0, 11>>,
  <<6, 0, 0, 12>>,
  <<6, 128, 0, 13>>,
  <<7, 0, 0, 14>>,
  <<7, 128, 0, 15>>,
  <<8, 0, 0, 16>>
]