Part 4 — Signals and video

What travels on a port, and what every patch jack owes whatever it carries. 7.1 defines the port list and patch safety; 7.2 the classes a patch jack may claim, audio, control CV, pitch CV, gate, trigger, clock, and video, and their ranges; 7.3 the video timing formats a video reference port lists. The patch jacks and the timing formats are EIS Core. 7.4 is the 75 Ω coaxial interface and its features: VID-REF-IN, VID-REF-OUT, VID-REF-PASSTHRU, and VID-REF-LOOPTHRU for a module's video reference ports behind the panel, and VID-75 for a picture on a coaxial jack.

Contents

• 7.1 Signals: The port list and patch safety
• 7.2 Patch signal classes: Audio, control CV, pitch CV, gate, trigger, clock, and video on patch jacks, and their ranges
• 7.3 Video timing: The formats a video reference port lists
• 7.4 Video on 75 Ω coaxial jacks (VID-75): The 75 Ω coaxial interface: the video reference ports VID-REF-IN, VID-REF-OUT, VID-REF-PASSTHRU, VID-REF-LOOPTHRU, the reference tree, and the coaxial cable

7.1 Signals

How a module declares what travels on each port, and the rules every patch jack follows whatever it carries.

Port list

A module shall publish a port list naming, for every port, its signal class or unclassified (SIG-001). A module with no ports publishes an empty list. Beside the class, the port list names the range a port claims when it is not the class default (7.2), and a port that generates or locks to a video reference lists its formats (7.3). The port list belongs in the manual, on the product page, or in a claim file.

A port that claims a class meets that class's limits in 7.2. A port that is neither a patch jack nor a video reference port, such as a coaxial picture jack, line audio, or MIDI, is listed as unclassified or by a name from Annex I; EIS places no requirement on it. EIS recommends labelling each port with its class, on the panel or in the manual.

Patch safety

These requirements apply to every patch jack on a module, whatever its class:

• A patch input shall withstand ±12 V indefinitely (SIG-002).
• A patch output shall withstand an indefinite short to 0 V or to another patch output (SIG-003).
• A patch output shall not drive the patch tip beyond ±12 V (SIG-004).

The ±12 V is the rails' nominal figure; a supply's 10 % start-up overshoot (SUP-006) is a rail figure, and no conforming output drives a tip beyond ±12 V while its rails are anywhere inside the supply's limits.

EIS recommends that every patch jack, and every RCA, BNC, or SMA jack, have its sleeve or shell insulated from the panel metal, so that no signal return runs through the panel and the case.

Video reference in a row

Video modules in a row share one video reference, and a module takes it behind the panel at a VID-REF-IN port, a rear 75 Ω coaxial jack under 7.4: fed from the VID-REF-OUT of a video reference generator, from the VID-REF-PASSTHRU of the module before it, or from a distributor, usually a bus board, whose VID-REF-PASSTHRU ports fan one reference out to one VID-REF-IN per module. A module claims each reference port it has by kind, VID-REF-IN, VID-REF-OUT, VID-REF-PASSTHRU, or VID-REF-LOOPTHRU. A patch jack shall carry patched signals only: a module shall neither take nor give its video reference at a patch jack, and no patch jack shall list a format of clause 7.3 (SIG-015). The reference is system configuration, wired once behind the panel, so patching never changes a module's timing. Informative Annex M describes the choices. Power for a video distribution product is ordinary module or case wiring, from the bus or a DC entry, and is not part of the feature.

7.2 Patch signal classes

The signal classes a patch jack may claim, and the ranges a class may take. Every patch jack also follows the patch-safety rules of 7.1: its input withstands ±12 V and its output never exceeds it.

All classes but MOD-VIDEO share one interface: about 1 kΩ source impedance into 100 kΩ loads. Each class has a nominal level, the level a port works at, a full scale, the swing its range allows, a class ceiling, and a damage limit (Terms): audio is nominally ±5 V and may swing to ±10 V, which is what an input has to accept. The levels are EIS figures; the gate thresholds follow A-100 practice (Scope 1.4).

Audio

MOD-AUDIO (SIG-005) is Eurorack audio at ±10 V peak on the patch tip, 7.07 V RMS for a full-scale sine. Coupling may be AC or DC.

Control CV

MOD-CV (SIG-006) is control voltage: envelopes, LFOs, offsets, and any other control that is not calibrated for pitch. Its level is the range the port claims, bipolar or unipolar at 1, 5, or 10 V full scale; B10, −10 to +10 V, when the port list names none.

Pitch CV

MOD-CV-1VOCT (SIG-007) is precision pitch CV: 1.00 V per octave. EIS recommends that 0 V correspond to C0, that the tracking accuracy of a pitch output be published in the manual, and that pitch ports be labeled 1 V/oct so that they are not mistaken for video ports; every oscillator has a tune control, so the absolute pitch at 0 V is a calibration figure, not a requirement.

Video

MOD-VIDEO (SIG-008) carries video on patch jacks, pictures, ramps, keys, and control at video rate, 0 to +1 V DC with a +1.2 V class ceiling. A MOD-VIDEO input shall present 100 kΩ ±10 % to 0 V at the patch tip (SIG-009). A MOD-VIDEO output shall drive through a 75 Ω ±5 % total series source impedance at the patch tip (SIG-010). A 75 Ω source into a 100 kΩ load arrives at almost unity gain; the cable's capacitance sets the bandwidth, about 70 MHz over 300 mm of 100 pF/m patch cable and about 20 MHz over a metre.

Video on a 75 Ω RCA, BNC, or SMA jack is a COAX-IN or COAX-OUT port (7.4), not a patch jack, and a module's video reference is a rear coaxial port, never a patch jack (SIG-015, V75-010); the formats a VID-REF-IN or VID-REF-OUT port lists are in 7.3.

Black, bandwidth, and delay

EIS recommends that a picture signal on MOD-VIDEO place black at 0 V and full scale (white, or a color channel at full saturation) at +1 V, so that a mixer or keyer can treat any two picture sources alike.

Two figures decide whether video patched through several modules stays sharp and stays in place on the screen, and EIS recommends that a video module publish both for each MOD-VIDEO path, as optional claim-file fields (bandwidth_mhz, delay_ns):

• Bandwidth: the −3 dB frequency of the path from input jack to output jack, into a 100 kΩ load. A path narrower than the format's luma bandwidth, about 5.5 MHz for SD and 30 MHz for HD, softens the picture.
• Delay: the time from an edge at the input jack to the same edge at the output jack, in nanoseconds. Two copies of one picture that reach a mixer by paths of different delay land side by side on the screen, offset by the difference; at 74.25 MHz one sample is 13.5 ns.

Gate, trigger, and clock

MOD-GATE (SIG-011), MOD-TRIG (SIG-012), and MOD-CLK (SIG-013) use the same receiver thresholds: high at +3 V or more, low at +1 V or less. MOD-GATE is a sustained high or low level. MOD-TRIG is a short pulse, at least 1 ms high. MOD-CLK is a repeating square wave. The gate line on the 16-pin header is BUS-GATE (6.6).

Ranges

A range is the full-scale swing a port is built for, named on the port list beside the class. A port claiming a range shall meet that range's limits as tabulated below: an output keeps its full-scale signal within the range's ceiling, and an input accepts the range's full swing without clipping (SIG-014).

EIS recommends that an output claim the smallest range that contains its full-scale signal, and an input the largest range whose full swing it accepts. A port that names no range has its class's default. Ranges do not relax patch safety. EIS recommends printing a range other than the default on the panel next to the jack.

The last column of the class table says which ranges each class takes. MOD-AUDIO at B5 or B1 is a quieter audio port. MOD-VIDEO takes U1 alone. A range on MOD-CV-1VOCT states the span of pitch CV a port accepts or produces; the scale stays 1.00 V per octave. Gate, trigger, and clock ports have thresholds, not ranges. For example, an envelope from 0 to +8 V is MOD-CV at U10, and an LFO at ±2.5 V is MOD-CV at B5.

Class table

The table is generated from data/signals.json. Source and load impedances are typical, except for MOD-VIDEO, whose are limits (SIG-009, SIG-010).

7.3 Video timing

EIS defines the video timing formats tabulated below: four standard-definition and fourteen high-definition rasters. The three 1080-line formats at 50, 59.94, and 60 frames per second are listed because display equipment defaults to them; on an analog component interface at 148.5 MHz they are rare, and a port lists one only when it generates or locks to it.

A module's port list shall name, for each VID-REF-IN and VID-REF-OUT port, every format from this clause the port locks to or generates, by its format ID (VID-001). A port may list one format or all of them; a VID-REF-PASSTHRU carries its VID-REF-IN's formats, and a patch jack lists none (7.1). A format that is not in the table is listed under its own name, and EIS says nothing about it.

When a listed format is selected or published on a port, that port's horizontal and vertical timing and its video sync structure shall match the format's publication within the tolerances that publication states, and for a progressive or high-definition format the row below is that publication's raster, sample for sample (VID-002). For the two interlaced formats the row is the reference raster: the publication's figures in microseconds, with the digital active line placed as ITU-R BT.601 places it against the timing reference OH, 16 and 122 luminance samples for the 525-line system and 12 and 132 for the 625-line system.

Composite color encoding (NTSC or PAL) applies only to the interlaced SD formats. A component output (YPbPr or RGsB) may use any listed format. A port that locks to an external video reference takes the selected format; EIS does not require format conversion.

Formats

The tables are generated from data/video_timings.json, where each row cites its SMPTE or ITU publication. Sample clocks are exact. SD formats are stated at 27.000 MHz: two samples per 13.5 MHz luma sample for the interlaced formats, so 525i59.94 has 1716 samples per line, and one per luma sample for the progressive formats, so 480p59.94 has 858. HD formats are at 74.25 MHz or 74.25/1.001 MHz, and the three 1080p formats at 50 Hz and above at 148.5 MHz or 148.5/1.001 MHz.

For an interlaced format, the vertical front porch and video sync counts cover both fields. Active lines are the count each publication gives for the format.

Interlaced formats in the publication's terms. The analog publications state a line in microseconds, with tolerances EIS does not restate: for 525i59.94 (SMPTE ST 170) a 63.556 µs line with a 4.7 µs video sync pulse, a 1.5 µs front porch, and 10.7 to 10.9 µs of blanking; for 625i50 (ITU-R BT.470) a 64 µs line with a 4.7 µs video sync pulse, a 1.5 µs front porch, and 12 µs of blanking. A port meets VID-002 inside those tolerances; the row is where a sample-domain design places the active line.

Line. Samples at the sample clock: total per line, active picture, front porch, video sync, back porch.

Frame. Lines per frame: total, active, front porch, video sync; the rate is the field rate of an interlaced format and the frame rate of a progressive one. SD marks the four standard-definition formats.

Phase

A module that locks to a video reference produces its output a fixed time after the reference. EIS recommends publishing that offset, horizontal and in nanoseconds, at each listed format, and any adjustment the module offers, so that several generators locked to one reference can be lined up on the screen.

Verification

A maker compares samples per line, lines per frame, field or frame rate, and video sync pulse width and placement with the tables and the cited publication. tests/video_timings_contract.py checks every row against a hardware-verified timing contract, clock for clock.

7.4 Video on 75 Ω coaxial jacks (VID-75)

VID-75 is the 75 Ω coaxial interface of EIS: video between products on 75 Ω coaxial cable with RCA, BNC, or SMA jacks. It carries the video reference of a row, black burst or bi-level or tri-level video sync of a 7.3 format, behind the panel from one source to every module that locks to it: this distribution is what conforms to EIS for interoperability, and a module claims it port by port with the features VID-REF-IN, VID-REF-OUT, VID-REF-PASSTHRU, and VID-REF-LOOPTHRU below. A feature describes what happens behind the panel or inside the case, so VID-75 is the interface those features use and is not claimed on its own. A picture on a coaxial jack on the front, composite or component video, is an external interface like line-level audio: it is listed in the port list with its Annex I class (VID-CVBS, VID-YPBPR, VID-RGBS) and the formats it carries, claims nothing, and EIS recommends that it take the COAX-IN or COAX-OUT form of this clause. A product with VID-REF-PASSTHRU ports beside its VID-REF-IN, usually a bus board, is a video reference distributor that fans the reference out to several modules, and a cable of the interface joins them. The tables are in data/video_75.json.

The front of a module is patched (7.2): the reference never reaches a patch jack (SIG-015), and a module that generates or locks to an external video reference takes or gives it at a video reference port on its rear (V75-010).

Video reference ports and claims

A module names what each of its video reference ports does, and claims it, with one feature per port kind. The difference between an input and an output is the one a buyer needs most: a VID-REF-OUT can be the row's reference, a VID-REF-IN follows it, and a pass-through is neither a source nor a second input.

A module that claims VID-REF-IN shall lock its video timing to the video reference at its VID-REF-IN port, a COAX-IN on its rear, and list the formats it locks to (V75-011). A module that claims VID-REF-OUT shall give a video reference of a listed format at its VID-REF-OUT port, a COAX-OUT on its rear, that it generates itself (V75-012); a copy of a reference it takes at VID-REF-IN is a VID-REF-PASSTHRU, not a VID-REF-OUT. A module shall claim VID-REF-PASSTHRU only with VID-REF-IN (V75-013); its VID-REF-PASSTHRU port shall be a COAX-PASSTHRU, a buffered copy of the reference at VID-REF-IN driven as a COAX-OUT into one COAX-IN load, and be marked PASSTHRU (V75-013). A module shall claim VID-REF-LOOPTHRU only with VID-REF-IN (V75-014); its VID-REF-IN shall then be a COAX-LOOPTHRU, two bridged jacks on one line with a termination switch that presents 75 Ω to 0 V across the line when on and no load when off, marked TERM, and the module shall lock the same with the switch on or off (V75-014).

The claim line names every port kind the module has: module (VID-REF-IN), module (VID-REF-IN, VID-REF-PASSTHRU), module (VID-REF-IN, VID-REF-LOOPTHRU), module (VID-REF-OUT), or module (VID-REF-IN, VID-REF-OUT) for a generator that also genlocks; its picture jacks are in its port list and add nothing to the line. Claiming any VID-REF feature brings the jack and port rules of this clause with it. A distributor claims VID-REF-IN and VID-REF-PASSTHRU, bus board (PWR-BUS-OUT, VID-REF-IN, VID-REF-PASSTHRU) (6.5); distribution is a capability of whatever product has those ports, not a product type.

Jacks

Every jack in a VID-75 tree shall be an RCA, BNC, or SMA jack (V75-001); EIS recommends that it be insulated from the panel (7.1). Its center pin shall carry the video signal and its shell shall be 0 V (V75-002). The three jack types are electrically the same here: an SMA jack is a 50 Ω connector and an RCA jack has no controlled impedance, but both are electrically short at video frequencies, below 100 MHz, so the discontinuity does not matter. A product picks the one that suits its panel, and a cable may change type from one end to the other. A video reference port shall be marked beside it as an input (IN), an output (OUT), a pass-through (PASSTHRU), or, for a loop-through pair, with its termination switch (TERM) (V75-016); V75-008, which asked the same of every coaxial port, is removed and its number stays unused.

Topology

A tree is the star of cables from one source to the VID-REF-IN of every module in it: the source is a VID-REF-OUT, or an external reference arriving at the VID-REF-IN of a distributor, and the branches are its VID-REF-PASSTHRU ports. The VID-REF-IN is the tree's designated input, named in the port list (V75-011), and terminated as every COAX-IN is (V75-009); V75-003 and V75-004, which asked for that separately, are removed and their numbers stay unused.

A VID-REF-OUT or VID-REF-PASSTHRU port shall drive one COAX-IN load, and an output shall not be split passively to several terminated ports (V75-005): a second termination on the same output drops the level to two thirds, and a third to half.

Video reference ports

Every video reference port shall be a COAX-IN (75 Ω to 0 V at the jack), a COAX-OUT (75 Ω series source driven at twice the line level), a COAX-PASSTHRU, or a COAX-LOOPTHRU port, never a patch jack (V75-015); the four port modes are defined in the summary, and a product with one claims the matching feature. V75-009, which asked the same of every coaxial jack including a picture port, and V75-006, which stated the rule for a port in a tree alone, are removed and their numbers stay unused: a picture port is an external interface, and a product cannot know how its owner cables a jack. A picture port, composite or component video on an RCA, BNC, or SMA jack on the front, or a digital port such as SDI on a BNC jack, is named by its Annex I class in the port list; EIS recommends the COAX-IN termination and the COAX-OUT back-termination of this clause for an analog picture port, so that it drives and loads a 75 Ω line the same way the reference does.

A module that generates or locks to an external video reference shall take or give it at a video reference port on its rear (V75-010): the reference is system cabling, wired once behind the panel, and the patch field carries patched signals only (SIG-015, 7.1).

The patch jacks of a video module use MOD-VIDEO (7.2). The video reference waveform, black burst or bi-level or tri-level video sync, follows the selected 7.3 format. Line level is the level of the signal's own standard at a terminated input: the 1 V p-p composite scale for composite video and black burst, ±300 mV for tri-level video sync. A buffered distributor may AC-couple its PASSTHRU outputs when its manual says so.

Cables

A VID-75 cable shall be a 75 Ω coaxial cable, with RCA, BNC, or SMA plugs, that connects center pin to center pin and shell to shell at both ends (V75-007).

Summary