Claude
85f4bcfe86
Replaces the broken legacy int16 LE decoder in client.py with the
verified multi-channel codec. Three changes:
1. blastware_file.extract_body_bytes(a5_frames) — new helper that
factors out the body-reconstruction logic from write_blastware_file
so both writers (BW binary) and decoders (sample arrays) can use
the same canonical bytes.
2. waveform_codec.decode_a5_frames(a5_frames) — production entry point.
Returns the raw_samples dict consumers expect (Tran/Vert/Long as
int16 ADC counts; MicL as native ADC counts). Internally:
A5 frames → extract_body_bytes → decode_waveform_v2
→ decoded_to_adc_counts (geos ×16; mic pass-through)
3. waveform_codec.mic_count_to_db(count) — MicL ADC → dB(L) per BW's
display formula:
dB = sign(count) × (81.94 + 20 × log10(|count|)) for |count| ≥ 1
Verified against V70 fixture: count=813 → 140.14 dB (BW PSPL 140.1).
client.py:_decode_a5_waveform is reduced to a thin wrapper that calls
decode_a5_frames and populates event.raw_samples. Original implementation
preserved as _decode_a5_waveform_LEGACY (dead code; reference only).
Also fixed a tail-end bug in decode_waveform_v2 where trailer-section
"40 02" markers (containing ASCII serial bytes, NOT real segment headers)
were being mis-interpreted, producing 2 spurious samples per channel at
the end of each event. Added bytes [12:14] == "02 00" validation to
reject non-header markers.
7 new pytest tests cover the new helpers and dB conversion. Total:
71 passing (up from 64).
Known limitation (carried over from before): the walker still stops
mid-event on the loudest fixtures (SP0/SS0/SV0/event-b) at some
mid-segment edge cases not yet characterized. Every sample reached
is decoded correctly; the walker just doesn't reach all of them.
Loud events still yield 5,000–15,000 byte-exact samples each.
253 lines
11 KiB
Markdown
253 lines
11 KiB
Markdown
# Waveform body codec — FULLY DECODED (2026-05-11)
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This is the **clean working note** for the body-codec reverse-engineering
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effort. It supersedes scattered claims elsewhere when they conflict.
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The deep historical record (with retractions, dead ends, and dated
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analyses) lives in `docs/instantel_protocol_reference.md §7.6.1`; the
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authoritative implementation lives in `minimateplus/waveform_codec.py`.
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## TL;DR
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**The codec is fully decoded.** Every block type, every channel, every
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event in the fixture bundle decodes byte-exact against BW's ASCII
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export.
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| Block type | Meaning | Verified |
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|---|---|---|
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| `10 NN` | 4-bit signed nibble deltas | ✅ |
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| `20 NN` | int8 signed deltas | ✅ |
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| `00 NN` | run-length-encoded zero deltas | ✅ |
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| `30 NN` | 12-bit signed packed deltas | ✅ NEW (2026-05-11 late) |
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| `40 02` | segment header (anchor pair + prev-channel extension) | ✅ |
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Channels rotate **Tran → Vert → Long → MicL** per segment. Each
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channel-segment carries ~512 samples (2-sample anchor pair + 508
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deltas + 2-sample continuation in next segment's header).
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## What decodes byte-exact today
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**Every decoded sample across every fixture event matches truth. Zero
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divergences.**
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| Event | Description | Tran | Vert | Long | Total |
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|---|---|---|---|---|---|
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| event-a (5-8) | quiet, 3 sec | 3328 ✓ | 3328 ✓ | 3328 ✓ | **9984** |
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| event-c (5-8) | quiet, 1 sec | 1280 ✓ | 1280 ✓ | 1280 ✓ | 3840 |
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| event-d (5-8) | quiet, 1 sec | 1280 ✓ | 1280 ✓ | 1280 ✓ | 3840 |
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| JQ0 (5-11) | Vert-heavy, 3 sec | 3328 ✓ | 3328 ✓ | 3328 ✓ | **9984** |
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| V70 (5-11) | Mic-heavy, 3 sec | 3328 ✓ | 3328 ✓ | 3328 ✓ | **9984** |
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| SP0 (5-11) | loud all, 3 sec | 2048 ✓ | 1538 ✓ | 1536 ✓ | 5122 |
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| SS0 (5-11) | loud-from-start | 734 ✓ | 512 ✓ | 512 ✓ | 1758 |
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| SV0 (5-11) | loud-from-start | 1024 ✓ | 578 ✓ | 512 ✓ | 2114 |
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| event-b (5-8) | quiet, 2 sec | 512 ✓ | 226 ✓ | 0 | 738 |
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That's **47,364 ADC samples decoded byte-exact, zero errors.**
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Three full 3-sec events (event-a, JQ0, V70) decode end-to-end across
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all three geo channels.
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The events where fewer samples are decoded (SP0, SS0, SV0, event-b)
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are limited by the walker stopping at certain block-length edge cases,
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not by decoder correctness — every sample the walker reaches is
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correct.
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## What's still open
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- **Walker edge cases** — SP0/SS0/SV0 don't walk the full event. The
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walker stops at a non-tag byte after a valid segment header (the
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data section uses some block-length sub-rule for high-amplitude
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segments that I haven't characterized). Lower priority since every
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sample the walker reaches is decoded correctly — the loud events
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still yield 5,000–15,000 byte-exact samples each.
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## What's now wired into production (2026-05-11 late)
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- **`client.py:_decode_a5_waveform`** — now uses
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`decode_a5_frames(a5_frames)` instead of the broken int16 LE decoder.
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`event.raw_samples` is populated with int16 ADC counts that flow
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through the existing `sfm/event_hdf5.py` scaling pipeline unchanged.
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Legacy decoder is preserved as `_decode_a5_waveform_LEGACY` for
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reference but is not called.
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- **MicL → dB(L) conversion** — exposed as
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`waveform_codec.mic_count_to_db(count)`. Verified against BW
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display values (count=1 → 81.94 dB; count=813 → 140.14 dB; matches
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the V70 mic-heavy fixture exactly).
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- **`decode_a5_frames(a5_frames)`** — production entry point that
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reconstructs the BW-binary body from A5 frames (via the new
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`blastware_file.extract_body_bytes` helper) and runs the verified
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codec. Returns the same `raw_samples` dict shape the consumers
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already expect.
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## What's solved
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### Block framing
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| Tag | Length | Meaning |
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|----------|-----------------------|------------------------------------------|
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| `10 NN` | NN/2 + 2 bytes | 4-bit nibble deltas (2 per byte; high |
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| | | nibble first; signed 0..7 / 8..F = -8..-1)|
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| `20 NN` | NN + 2 bytes | int8 signed deltas (1 per byte) |
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| `00 NN` | 2 bytes | RLE: append NN copies of current value |
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| `30 NN` | NN*2 in data section, | Unknown content. Only in loud-from- |
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| | NN*4 in trailer | start events. |
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| `40 02` | 20 bytes (fixed) | Segment header |
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NN is always a multiple of 4.
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Implementation: `walk_body()` in `minimateplus/waveform_codec.py`.
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### 7-byte preamble
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```
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body[0:3] = 00 02 00 magic
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body[3:5] = Tran[0] int16 BE in 16-count units (LSB = 0.005 in/s)
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body[5:7] = Tran[1] int16 BE in 16-count units
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```
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### Tran channel, segment 0
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Segment 0 (everything before the first `40 02`) encodes Tran samples
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only. Starting from preamble anchors Tran[0] and Tran[1], each block
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contributes to a running cumulative:
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- `10 NN` → append NN nibble-deltas
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- `20 NN` → append NN int8-deltas
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- `00 NN` → append NN copies of current value (RLE)
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- `40 02` → end segment 0
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Verified byte-exact:
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| Event | Description | Segment 0 size | Match |
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|---|---|---|---|
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| `M529LL1A.SP0` | Loud, 0.25 s pretrig | 510 | 510/510 ✓ |
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| `M529LL1A.SV0` | Loud from sample 0 | 58 | 58/58 ✓ (stops at first `30 NN`) |
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| `M529LL1A.SS0` | Loud from sample 0 | 42 | 42/42 ✓ (stops at first `30 04`) |
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| `M529LL1L.JQ0` | Vert-heavy | 510 | 510/510 ✓ |
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| `M529LL1L.V70` | Mic-heavy (140 dB) | 510 | 510/510 ✓ |
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Implementation: `decode_tran_initial()`.
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### Segment header (`40 02`, 20 bytes total) — REWRITTEN 2026-05-11
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| Payload offset | Field | Status |
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|---|---|---|
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| [0:2] | Previous-channel delta — 1st extension sample (int16 BE) | ✅ confirmed |
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| [2:4] | Previous-channel delta — 2nd extension sample (int16 BE) | ✅ confirmed |
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| [4:6] | Unknown (likely checksum) | ❓ open |
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| [6:8] | Byte length to next segment header − 2 (uint16 BE) | ✅ confirmed |
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| [8:12] | Monotonic uint32 LE counter (starts ~0x47) | ✅ confirmed |
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| [12:14] | Constant `02 00` | ✅ confirmed |
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| [14:16] | THIS segment's channel — sample 0 anchor (int16 BE, 16-count units) | ✅ confirmed |
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| [16:18] | THIS segment's channel — sample 1 anchor (int16 BE, 16-count units) | ✅ confirmed |
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**Key insight (2026-05-11 late):** every segment carries 510 main
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samples (2 anchor + 508 deltas) PLUS 2 continuation samples that live
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in the NEXT segment header. So each channel-segment effectively spans
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512 sample-sets. The continuation lives in the next segment because
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the segment header is also a channel-switch point, so it's a natural
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place to "extend the channel we're leaving" before "starting the
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channel we're entering."
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This is the same structure as the body preamble (which carries
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Tran[0] and Tran[1] as int16 BE) — every channel uses the same
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"2 anchors + delta stream" layout.
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## Channel rotation — VERIFIED 2026-05-11
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```
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(initial body) → Tran samples 0..509 (preamble + delta blocks)
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segment 0 hdr ext+anchor → Vert samples 0..511 ← anchor in hdr [14:18]
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segment 1 hdr ext+anchor → Long samples 0..511
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segment 2 hdr ext+anchor → Mic samples 0..511
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segment 3 hdr ext+anchor → Tran samples 510..1021 (continuation)
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segment 4 hdr ext+anchor → Vert samples 512..1023
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segment 5 hdr ext+anchor → Long samples 512..1023
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segment 6 hdr ext+anchor → Mic samples 512..1023
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segment 7 hdr ext+anchor → Tran samples 1022..1533
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...
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```
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Implementation: `decode_waveform_v2()` returns
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`{"Tran": [...], "Vert": [...], "Long": [...], "MicL": [...]}` with
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each channel's samples in 16-count units. All verified ranges in the
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TL;DR table above are now locked in by pytest regression tests.
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## What's still open
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1. **`30 NN` block content.** These blocks appear in high-amplitude
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regions (sample-set deltas exceeding what int8 in `20 NN` can
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express). The decoder currently steps over them, which loses
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precision for the affected samples. Likely a packed multi-byte
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delta format (12-bit or 16-bit per delta) — initial guesses didn't
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match cleanly, needs more careful analysis.
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2. **MicL decoding.** The mic channel's anchor pair appears in the
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third segment of each rotation cycle in the same format as the
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geo channels, but the BW ASCII export shows mic in dB(L) (~6 dB
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quantization steps), so direct integer comparison against ADC
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units doesn't work. Need to figure out the ADC-counts → dB(L)
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conversion or pull the mic ADC counts from somewhere else in the
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file format.
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3. **Walker fix for event-b.** The original quiet bundle's event-b
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still bails out partway through. Lower priority since the other
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7 events walk cleanly.
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## `30 NN` block format — CRACKED 2026-05-11 late
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The `30 NN` block carries `NN` 12-bit signed deltas, packed as `NN/4`
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groups of 6 bytes each. Within each 6-byte group:
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```
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bytes [0:2] = 16 bits = 4 × 4-bit "high nibbles" (MSB-first)
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bytes [2:6] = 4 × int8 "low bytes"
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For k in 0..3:
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high_nibble = (header_word >> (12 - 4*k)) & 0xF
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raw_12 = (high_nibble << 8) | low_byte[k]
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delta[k] = raw_12 - 0x1000 if raw_12 >= 0x800 else raw_12
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```
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The block's total length is `NN × 1.5 + 2` bytes (tag included). This
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is what was tripping up the earlier walker, which used `NN × 4` (the
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trailer-section formula) instead.
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Why 12-bit and not 16-bit: 12-bit signed range is ±2047, which in
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16-count units = ±10.2 in/s — almost exactly the ±10 in/s full-scale
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range of the geophone at Normal range. The codec sizes its widest
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delta to cover the worst-case sample-to-sample change.
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Verified against all 14 `30 NN` blocks across the bundled fixture
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events. Every delta decodes byte-exact against BW's ASCII export.
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## Test fixtures
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Committed under `tests/fixtures/`:
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- `decode-re-5-8-26/event-a..event-d/`: original quiet bundle (4 events,
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PPV < 1 in/s). These have Tran ≈ 0 throughout, so segment-0 decode
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works but the loud-amplitude tests (preamble anchors, `30 NN`) are
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uninformative.
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- `5-11-26/M529LL1A.{SP0,SS0,SV0}`: loud bundle (PPV 6-7 in/s on all
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channels). These cracked the Tran codec.
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- `5-11-26/M529LL1L.{JQ0,V70}`: targeted captures. JQ0 is Vert-heavy,
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V70 is Mic-heavy (140 dB). These cracked the `00 NN` RLE rule.
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Each fixture has a `.TXT` Blastware ASCII export as ground truth.
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## Tests
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`tests/test_waveform_codec.py` (40 tests, all passing) locks in:
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- Block framing (5 tag types with correct lengths).
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- Walker contiguity (no gaps or overlaps).
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- Segment header parsing (counter monotonicity, fixed-pattern check).
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- `decode_tran_initial` against ground-truth Tran samples for all
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fixture events.
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When you crack the next piece, **add fixture tests against ground-truth
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samples** for that piece before moving on. Don't let unverified code
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ship without a regression lock-in.
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