Log 038 — "A record from one microphone" — is the night CosmicFest went from
"educated guess game", PLN's phrase, to a pipeline. It carries the measurements
that reshaped the job and a correction to my own previous commit.
eda_stems.py is the mastering EDA a stemless gig could not otherwise have, and it
exists to answer three specific questions rather than to print statistics.
Is the 8-16 kHz deficit cymbals or codec noise? The master measured 0.12% of
total energy up there and the air shelf was deliberately held to +5 dB instead of
the +12 the deficit suggests, because a 320 kbps MP3 puts hiss in that band
alongside hats. A broadband boost cannot tell the two apart; a per-stem view can.
If the HF lives in `drums` it is cymbals and the shelf can open, and if it is
spread evenly across all four it is noise and the shelf stays shut.
Where is the kick? project_floor_problem measured the kick audible in only 59% of
OPAL-26, from real orbit stems. This asks the same question of a gig that has
none, via 40-120 Hz activity over time, thresholded relative to each track's own
p95 rather than an absolute dBFS — a fixed threshold on a quiet room-coloured
source measures the recording level, not the kick. Reported per track so a floor
that drops out gets named instead of averaged away.
And how much does local-versus-global separation actually differ? It compares
each section's stem against the same span cut out of the global stem:
correlation says whether the model made the same decision, the RMS delta says
whether normalisation changed the level. That comparison is the reason the
chunked writer had to be length-exact.
Presence is gated before any stem is compared to another, and demucs' own source
names are treated as hypotheses — feedback_label_and_lens applies to a
separator's labels as much as to a sample's filename.
finish_cosmic.sh + cosmic-finish.service exist because of a structural mistake I
nearly shipped. The master and demucs runs are systemd units so they outlive the
session, but every step AFTER them — split, verify, EDA — was sitting in my
session. PLN said "your autonomous now going to bed tell me results tomo", so a
teardown would have left him with rendered masters and nothing else. The unit is
ordered After= both producers, so systemd does the waiting instead of a polling
loop, and it leaves FINISH_SUMMARY.txt on disk that stands on its own. Wants=
rather than Requires=, deliberately: a club-target miss or a demucs failure must
not cancel the split of a perfectly good streaming master.
The log also corrects commit 37eb401f, which claimed the chunked demucs path was
about twice as fast. It is not, and the claim came from a broken metric: I counted
directories under stems_demucs/sections/, but a directory appears the moment
chunked_separate opens its writers, so the count measures sections STARTED, not
finished. libsndfile buffers on top of that, so three of four in-flight sections
sat at 44 bytes — a bare WAV header — after nine minutes of genuine work.
Measured properly by mtime and flushed bytes, a worker runs at about 4.3x
realtime under four-way contention plus the master render. Chunking fixed the
OOM kill; it did not demonstrably make anything faster.
