User intuition (16-bit) + 12-bit packing hypothesis + the int16 ADC
range constraint led to the final piece.
30 NN block format (CONFIRMED across all 14 blocks in the fixture
bundle):
NN 12-bit signed deltas packed as NN/4 groups of 6 bytes each.
Within each group:
bytes [0:2] = 16 bits = 4 × 4-bit high nibbles (MSB-first)
bytes [2:6] = 4 × int8 low bytes
delta[k] = sign_extend_12((high_nibble[k] << 8) | low_byte[k])
Block length = NN × 1.5 + 2 bytes (tag included). Earlier walker
used NN × 4 which is only correct in the TRAILER section.
Why 12-bit: ±2047 in 16-count units ≈ ±10 in/s = the geophone's
full-scale range at Normal sensitivity. The codec sizes its widest
delta to cover the worst-case sample-to-sample change.
Results: every decoded sample across all fixture events matches truth
byte-exact. ZERO divergences.
event-a: 9984 samples (full event, all 3 geos)
event-c: 3840 (full event)
event-d: 3840 (full event)
JQ0: 9984 (full event)
V70: 9984 (full event)
SP0: 5122 (walker stops early on edge cases)
SS0: 1758
SV0: 2114
event-b: 738
TOTAL: 47,364 ADC samples verified, zero errors.
Three full 3-sec events decode end-to-end across all three geo
channels. The events where fewer samples decode (SP0/SS0/SV0/event-b)
are limited by walker robustness issues past the first few segments,
NOT by decoder correctness.
64 tests pass (up from 55). Files: minimateplus/waveform_codec.py
(new 30 NN decode + corrected walker length), tests/test_waveform_codec.py
(new full-event regression tests), docs/* (updated status everywhere),
analysis/test_30nn_hybrid.py (new — the analysis script that confirmed
the format).
User asked the right question: do events without 30 NN blocks decode
fully? Answer: YES.
event-a: Tran 3328 ✓ Vert 3328 ✓ Long 3328 ✓ (28 segments, 0 '30 NN')
event-c: Tran 1280 ✓ Vert 1280 ✓ Long 1280 ✓ (12 segments, 0 '30 NN')
event-d: Tran 1280 ✓ Vert 1280 ✓ Long 1280 ✓ (12 segments, 0 '30 NN')
17,664 ADC samples decoded byte-exact against BW's ASCII export.
Zero divergences across event-a, event-c, event-d.
This means the codec is FULLY SOLVED for any event without 30 NN
blocks. The remaining gap is the 30 NN block format only — used for
high-amplitude regions where deltas exceed int8 range. For quiet
events (or quiet stretches of loud events), the decoder is complete.
9 new regression tests bring the total to 55, all passing.
Files: tests/test_waveform_codec.py + docs/waveform_codec_re_status.md
+ new analysis/verify_quiet_bundle.py.
The segment-channel scoring analyzer (from scratch/next_experiment_skeleton.py)
ran and immediately confirmed the rotation hypothesis:
SP0 seg 0: best fit Vert 508/508 ✓
SP0 seg 1: best fit Long 508/508 ✓
SP0 seg 3: best fit Tran 508/508 ✓ (Tran continuation)
SP0 seg 5: best fit Long 508/508 ✓
SP0 seg 9: best fit Long 508/508 ✓
V70 seg 0: best fit Vert 508/508 ✓
V70 seg 1: best fit Long 508/508 ✓
Channels rotate Tran → Vert → Long → MicL per 40 02 segment header.
Also discovered the segment header has DOUBLE duty: bytes [14:18] anchor
the NEW segment's channel (2 samples as int16 BE in 16-count units), AND
bytes [0:4] extend the PREVIOUS channel by 2 more samples (2 deltas as
int16 BE). This is the same "2 anchors + delta stream" structure as the
body preamble for Tran.
decode_waveform_v2 now returns full per-channel sample dicts.
Byte-exact verified ranges:
V70: Tran 512, Vert 512, Long 512 (all first segments)
JQ0: Tran 512, Vert 258
SP0: Long 1536 (all 3 L segments)
Still open: the 30 NN block format (high-amplitude packed deltas) —
appears mid-segment when single-byte deltas can't carry the magnitude.
6 new tests bring the count to 46. All passing.
Three "truth layers" had drifted apart between commits. Fixed:
1. waveform_codec.py docstring rewritten from the 2026-05-08
"structural framing only" state to the 2026-05-11 "Tran segment 0
solved + segment-header partially decoded" state. Killed stale
"~80 sample-sets per segment" language (real segments are
flash-page-byte-sized, not sample-count-sized; observed first-segment
sizes are 42-510 samples depending on signal). Killed stale
"preamble is 7 or 9 bytes" language (always 7).
2. docs/instantel_protocol_reference.md §7.6.1: added a clear
"CURRENT STATUS" box at the top with a status table. Replaced the
stale "~80 sample-sets" line with the verified per-event segment
sizes. Merged two redundant segment-header field-table sections.
3. docs/waveform_codec_re_status.md (NEW): clean working-status doc.
Solved / not solved / hypothesis / next experiment / fixtures /
tests. The protocol reference remains the historical Rosetta
Stone; this new file is the current-truth working note that
shouldn't accumulate fossil layers.
4. CLAUDE.md §"Waveform body codec": prominent warning box at top —
"DO NOT TRUST decoded sample arrays yet." BW binary passthrough
is the only sample-bearing output to trust until the decoder
lands. Added a "Next experiment" subsection pointing the next
pass at the segment-channel scoring analyzer.
40 tests still pass.
Claude