# 033 — Fourteen tracks from one microphone

**Landed 2026-08-29.** PLN dropped a file in chat: *"boom downloaded cosmic set!
ZOOM0067.MP3 can you find the tracks back? its an interesting test actually :P"*

A 63-minute handheld stage-mic MP3 of a gig with no stems and no session log. Every
boundary lens the toolbox owned needed something that recording did not have.
Orbit-activity needs stems. The gig-log's `track` events ARE the tracklist, and the
recorder never ran. Gap detection assumes a set stops between tracks, and a livecoded set
does not.

Final score against PLN's ears: **12 of 14 tracks named correctly**, 81% of the set
labelled, 85% of the labelled overlap right.

## The first pass measured loudness

I built Shazam-style landmark fingerprints of rare sample banks and reported the results,
and every bank occupied 375 of 378 time bins. Three things were wrong, and none of them
was a threshold.

**Offset consistency was missing entirely — and it is half the algorithm.** Wang's 2003
paper is explicit: real matches agree on a time offset, so the scatterplot shows a
diagonal and the offset histogram spikes. Adding it took the top hit from noise to **85%
of 1244 hashes agreeing on one offset**.

**Raw counts measure loudness, not similarity.** Measured, not assumed: 8 of 18 banks had
their global peak in the final minute at 1.3-2.5x density. A loud broadband finale makes
more spectral peaks, so it matches *everything* better.

**And fixed offset is wrong for this material anyway.** Sonnleitner, Arzt & Widmer's
ISMIR 2016 DJ-mix work allows the offset line a free slope, because a DJ plays material at
a different rate — and a livecoder changing `setcps` across 80 to 170 BPM does the same.

## PLN's reframe, which was the actual unlock

*"so it meas comparign to prior recs, of each track of the opal songs for example (almost
the same lineup in the end!), can be fertile?"*

Yes, and it reframes the task. A 0.4 s dry one-shot through a PA and a 320 kbps encode is
below any landmark method's detection floor by construction. But `Prod/Opal26_master/tracks`
holds fifteen ear-verified per-track renders of 154-524 s each, played by the same
performer from the same sample library — and Montreuil-26 adds fifteen more, six of them
tracks OPAL never had. That is minutes of reference per track instead of fractions of a
second, and it turns sample detection into **version identification**, where the
literature is unambiguous: match sequences of features, not exact time-frequency points.

`punkachien` landed at margin 1.06 purely because Montreuil supplied that render.

## Three attempts at tempo, because the first two measured nothing

1. `librosa.feature.tempo` returned 107-130 for every segment of an 80-170 BPM set. That
   is its log-normal prior centred on 120. A lens whose output is its prior measures
   nothing.
2. Mode of inter-onset intervals on the full mix: 233-648 BPM — it locks onto the fastest
   subdivision, the hats. Its apparent matches were hollow too: five octave multiples at
   5% tolerance passes roughly a quarter of *random* values.
3. Autocorrelation of the **40-120 Hz kick band**. Validated on six cases chosen because
   their declared tempos are known and well separated, so the test could fail: bombe
   123.9/124, punkachien 170.1/170, vague_de_crime 120.1/120, do_it_right 178.3/2 =
   89.15/89. Four exact to 0.1%.

That validation is what licensed the overrides. An instrument that agrees where it should
is one whose **disagreements carry information**.

## The same bias, three times, in three costumes

`locate` normalised by reference size. `crossmatch` did not, and the number said so:
correlation(reference length, seconds won) = **+0.586**. Ceci (524 s) and Piment (506 s)
won most of the set; WAP and REVOLUTION won nothing. Fixed by standardising each track's
score column over the whole query — "how UNUSUALLY similar" rather than "how similar".

Then the fusion grew it a third time: counting each top-3 tempo candidate as a vote let
`cafe_bouillant` beat `ouais_je_funk`, which measured 120.1 against a declared 120. A
perfect match, demoted by an alphabetical tie.

## PLN's ears beat my reporting, twice

He heard a rose_rouge sample inside a seam I had labelled `quand_on_decolle`, and said he
was sure he had played `something_about_drums` in a stretch I reported as unclaimed. Both
were **already in my data**: I had 86 offset-consistent detections and had printed 4,
because the report showed each bank's single best window and discarded temporal extent —
which for this question is the informative part.

    rose        -> rose_rouge            22:35-24:00 (max cons 0.81) ... 31:30
    movie_paris -> something_about_drums   6:15 (0.62), 10:30 (0.49)

His diagnosis of the fix was also right: *"its almost tfidf we should do here. when we
know rose sample is around a time slot, its a tell. when we see e.g. _jungle_BreakS_, it's
way less idf relevant."* With one correction from measuring it — plain log-IDF is too
flat, giving `jungle_breaks` (df=80) 0.50x the weight of `rose` (df=2), a 2x penalty for
being 40x more common. **1/df** gives 0.0125 versus 0.50.

## A negative result, and a hypothesis that died

The weighting let MAX_DF rise from 6 to 40, taking fingerprint coverage from 15/23 to
**23/23** candidate tracks — and it added **zero** evidence. I guessed reference duration
was the binding constraint. Wrong: correlation with best consistency is **-0.144**, and
the three longest references are among the worst detectors. Then the confound surfaced —
`suns_keys` belongs to `blue_gold`, which PLN did not play, so its low score is a **true
negative**. Failures and true negatives are indistinguishable without the setlist, so the
cause is recorded as unestablished rather than explained away.

## Both remaining failures are one failure

`perfect` was called gimme_acid; the improvised outro was called REVOLUTION. All five
ghosts — blue_gold, desire, gimme_acid, quand_on_decolle, REVOLUTION — are the same
mechanism: crossmatch can only choose among tracks it holds a prior render of, so audio
from a track it has never heard lands on the nearest thing it has.

Structural, not a threshold. **The fix is one render per track**, and it compounds: every
future set recovery gets easier.

## And a track that only exists live

The final 103 seconds, per PLN: *"thissegment is pure dubsiren noise and fun ahahah it
could be called 'Outro Dub Siren' ahah"*. No reference-based lens could ever have named
it. Worth cataloguing under its own name if the set is released.
