Lowband
A Hi8 tape on a Video8 deck, for Resolume
What it does
An FFGL effect for Resolume Arena and Avenue. Hi8 is Video8 with the luma's FM carrier moved up: sync tip 5.7 MHz and peak white 7.7 MHz, 2.0 MHz of swing where Video8 has 4.2, 5.4 and 1.2, and a 0.47 µs pre-emphasis where Video8's is 1.3 µs. The colour, recorded under the luma at 732 kHz (PAL) or 743 kHz (NTSC), stayed where it was. Lowband models the luma as that FM signal, recorded, band-limited, limited and demodulated by counting zero crossings at 40.5 MHz on the CPU, and plays a Hi8 tape through a Video8 deck's channel, scale and de-emphasis.
Here's what comes out of that without being drawn. The deck maps 1.2 MHz of swing to the whole picture and the tape swings 2.0, so the contrast is 5/3 too high. Hi8's short pre-emphasis under Video8's long de-emphasis makes a step land half-way at once and creep the rest of the way with 1.3 µs, which is the glow trailing every highlight. The same mismatch on the sync pulse leaves the back porch still settling when the monitor clamps black there, so the black lifts about 5 %. A bright edge's pre-emphasis overshoot reaches 10 MHz, outside the Video8 deck's band, and the demodulator loses the crossings: a black streak. And white's carrier sits furthest outside the band, so under tape noise the highlights break up first while the darks hold.
Play a Video8 tape on the same deck, or either tape on a Hi8 deck (which plays each format in its own mode), and the picture is clean: those are the references. Tape Noise sets a carrier-to-noise ratio, Head Clog adds Wallace's spacing loss (54.6 dB per wavelength of spacing), Dropouts drop the carrier, and Sync AGC restores the sync's height, which only takes back part of the excess because the sync measures short too.
It isn't Colourunder, which does VHS's colour, head switch and tracking with a luma that's never a carrier. Lowband is the luma carrier on its own, and the two stack. The look is the model's prediction: I couldn't find a recording of a real Hi8 tape on a Video8 machine to check it against, and the deck's band is a decoder's filters standing in for a real deck's head and equaliser.
- The luma as a real FM signal: recorded, filtered, limited and demodulated at 40.5 MHz
- Hi8's 5.7-7.7 MHz carrier read by a deck built for Video8's 4.2-5.4 MHz
- Contrast 5/3 too high, a 1.3 µs glow, a lifted black and black streaks, all from the mismatch
- Highlights that break up first under tape noise; a Video8 tape stays clean
- Head Clog as Wallace's spacing loss, dropouts, and a sync AGC
- Video8 and Hi8 recordings and decks, PAL and NTSC
- Universal macOS bundle and a Windows x64 DLL
Where it stands
v0.1.0, and early days. It has never been loaded into Resolume on macOS. On Windows it has: a build of v0.1.0 loads, registers and renders in Resolume Arena 7.27.1 on software rendering (no GPU), with all 14 host controls as declared and 7 of the 9 that can move the picture shown doing so. Dropouts and Standard couldn't be told apart from the per-frame tape noise there. The deck is measured by an offline harness driving the real plugin class at three rasters and on Apple's software renderer: the recorded carriers, counted crossing by crossing, are the formats' own, a deck playing its own format gives back a flat field, a Hi8 tape on the Video8 deck has a gain of 1.66675 against the 2.0 / 1.2 the formats predict, the glow decays with the deck's own 1.3 µs de-emphasis, the lifted black is within 4 % of its prediction, and at the same tape noise a Hi8 tape's white is 2.6 times as noisy as its black, against 1.02 for a Video8 tape. Twelve models broken on purpose each fail their check, and all 8 controls change the picture. I couldn't find a recording of a real Hi8 tape on a Video8 machine to compare against, so the look is the model's prediction, and the deck's band is a decoder's stand-in. It hasn't been timed on Windows, and there's no OpenFX port and no presets. There's a user guide and a browser demo (a JavaScript port of the engine, checked against the C++ by a script in the repository, but trusted on the page). Try it in your own rig before you trust it in a show.
Watch it running
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