====== envelop point Y coordinate trees ======
These trees are built as [[canonical huffman trees]]. Remember that negative values are 2's complement encoded and thus appear after the positive values in the trees.

===== envelope y tree ======
  * 0-3: 7 bit
  * 4: 5 bits
  * 5: 3 bits
  * 6: 4 bits
  * 7: 1 bits
  * 8: 3 bits
  * 9: 4 bits
  * 10,11: 6 bits
  * 12-15: 7 bits

===== delta y tree =====
  * -8..-5: 9 bits
  * -4: 7 bits
  * -3: 4 bits
  * -2: 2 bits
  * -1: 1 bit
  * 0: missing
  * +1: 3 bits
  * +2: 5 bits
  * +3: 7 bits
  * +4..+7: 9 bits

===== delta-to-master y tree =====
  * -8..-5: 9 bits
  * -4: 8 bits
  * -3: 7 bits
  * -2: 4 bits
  * -1: 3 bits
  * 0: 1 bit
  * +1: 2 bits
  * +2: 5 bits
  * +3: 8 bits
  * +4..+7: 9 bits

===== delta-to-prev-envelope y tree =====
  * -8..-5: 9 bits
  * -4: 7 bits
  * -3: 5 bits
  * -2: 3 bits
  * -1: 3 bits
  * 0: 1 bit
  * +1: 3 bits
  * +2: 4 bits
  * +3: 7 bits
  * +4..+7: 9 bits