In professional broadcast production, multiple cameras, video switchers, routers, and recording devices often need to operate together with precise timing.

One of the technologies used to accomplish this is genlock.

Genlock allows compatible video equipment to synchronize its timing to a common reference signal. This helps production systems maintain predictable timing relationships between multiple video sources.

But what exactly is genlock? What is the difference between black burst and tri-level sync? And why are 75-ohm BNC cables commonly used for video reference connections?

This guide explains how professional broadcast synchronization works and what to consider when selecting reference cables for your installation.

WHAT IS GENLOCK?

Genlock, short for generator locking, is a method of synchronizing compatible video equipment to a common timing reference.

In a broadcast facility, multiple cameras and video devices may otherwise operate using their own internal timing generators.

Even when those devices are configured for the same video format and frame rate, their timing may not be aligned.

Genlock allows supported equipment to lock its internal video timing to a shared reference.

This is particularly useful in production environments where multiple video signals must be switched, routed, or processed together.

WHY IS GENLOCK IMPORTANT IN BROADCAST PRODUCTION?

Professional production environments frequently combine video signals from multiple sources.

These may include:

• Studio cameras
• Broadcast video switchers
• Video routers
• Graphics systems
• Recording and playback equipment
• Video processing systems
• Production control rooms

When equipment shares a compatible timing reference, engineers can establish consistent timing relationships throughout the facility.

This is especially useful for systems designed to perform clean switching between synchronized video sources.

Some video switchers include frame synchronizers that can accommodate asynchronous inputs. However, frame synchronization can introduce processing delay and may not replace the benefits of a properly timed broadcast system.

Genlock is therefore an important consideration in many professional production workflows.

HOW DOES GENLOCK WORK?

A typical genlock system begins with a master synchronization generator.

The generator produces a reference signal that compatible equipment can use to synchronize its internal timing.

Reference signals are commonly distributed using 75-ohm coaxial cable with BNC connectors.

In this example, the master generator provides the timing reference.

A compatible reference distribution amplifier delivers that signal to multiple devices.

Each device is configured to use the appropriate external reference.

The result is a group of devices operating in synchronization with the same timing source.

WHAT IS BLACK BURST SYNC?

Black burst, sometimes called color black or bi-level reference, is an analog video reference signal used in professional broadcast synchronization.

It contains the timing information associated with a standard-definition composite video signal, including synchronization pulses and color burst information.

The picture portion is held at black level.

Black burst has historically been widely used for synchronizing broadcast facilities and equipment.

It remains useful in facilities containing compatible equipment that accepts this reference format.

Common applications include:

• Legacy broadcast equipment
• Mixed-format production facilities
• Compatible studio cameras
• Video switchers and routers
• Broadcast synchronization systems

Important: Black burst is a timing reference, not a replacement for the SDI video signal carrying the camera image.

WHAT IS TRI-LEVEL SYNC?

Tri-level sync is another analog reference signal commonly used in high-definition broadcast systems.

Unlike traditional bi-level synchronization, tri-level sync uses three signal levels to establish precise timing information.

Its waveform transitions through a central reference level, providing a well-defined timing point.

Tri-level synchronization is supported by many professional HD cameras, switchers, and video processing devices.

Some UHD production systems also accept compatible HD tri-level or black burst references, depending on equipment design.

Always check the equipment manufacturer's supported reference formats before selecting a synchronization generator.

BLACK BURST VS. TRI-LEVEL SYNC

Neither format is universally correct for every installation.

The appropriate reference depends on the video format, frame rate, and supported synchronization capabilities of the equipment.

WHY DO GENLOCK SYSTEMS USE 75-OHM BNC CABLES?

Professional analog video reference interfaces commonly use nominal 75-ohm connections.

A properly constructed 75-ohm coaxial cable provides a suitable transmission path between compatible reference equipment.

Professional BNC connectors provide secure connections that are familiar throughout broadcast facilities.

When selecting a reference cable, consider:

• 75-ohm cable impedance
• Compatible 75-ohm BNC connectors
• Appropriate cable length
• Reliable connector termination
• Suitable shielding and mechanical construction
• Proper equipment termination
• Installation and routing requirements

Reference signals generally have different bandwidth requirements from 12G-SDI video.

Therefore, a cable does not need to be 12G-SDI rated simply to carry a compatible analog genlock reference.

However, high-quality professional 75-ohm video coaxial cable can be a practical choice for broadcast reference distribution.

CHOOSING BELDEN COAXIAL CABLE FOR VIDEO REFERENCE

Belden 4505R RG59

Belden 4505R is a professional 75-ohm RG59 coaxial cable used in demanding broadcast video applications.

Its full-size construction makes it a useful option for professional equipment racks, studios, and facility installations.

AV-Cables manufactures BNC-to-BNC assemblies using genuine Belden 4505R and precision 75-ohm connectors.

These assemblies can be considered for compatible 75-ohm analog video reference applications when the complete installation meets the equipment manufacturer's requirements.

Explore Belden 4505R RG59 BNC Cable Assemblies

Belden 4855R Mini RG59

For installations where equipment racks have limited space, Belden 4855R offers a compact Mini RG59 construction.

Its smaller outside diameter can help reduce cable congestion in high-density broadcast installations.

AV-Cables offers Belden 4855R assemblies with professional 75-ohm BNC connectors and configurable lengths.

Explore Belden 4855R Mini RG59 BNC Cables

Selection note: Confirm the reference signal type, connector requirements, cable length, and termination specifications before using any cable assembly in a synchronization system.

GENLOCK VS. SDI: WHAT IS THE DIFFERENCE?

Genlock and SDI are related to professional video production, but they perform different functions.

SDI carries digital video and, when supported, embedded audio and ancillary data.

Genlock provides a timing reference used to synchronize compatible equipment.

For example, a broadcast camera may have two separate BNC connections:

• SDI OUT: Sends the camera's digital video signal to a switcher, router, or monitor.
• GENLOCK IN or REF IN: Receives a compatible external timing reference.

These connections should not be confused simply because both use BNC connectors.

Connecting a reference signal to the wrong equipment input will not provide the intended operation.

Always verify the equipment's connector labels and technical documentation.

GENLOCK VS. WORD CLOCK: ARE THEY THE SAME?

No. Genlock and word clock serve different synchronization purposes.

Genlock is associated with video timing, while word clock is used to synchronize the sampling clocks of compatible digital audio equipment.

Both may use 75-ohm coaxial cable and BNC connectors, but the signals are not interchangeable.

A cable's physical construction does not convert one reference format into another.

For professional digital audio systems, AV-Cables also manufactures dedicated 75-ohm BNC word clock cable assemblies.

When designing systems that require synchronized audio and video, confirm the supported reference formats and distribution requirements for every device.

DO GENLOCK CABLES NEED 75-OHM TERMINATION?

Proper termination is an important part of analog reference distribution.

Professional reference systems are generally designed around 75-ohm transmission paths.

However, not every reference input is terminated in the same way.

Some equipment provides internal 75-ohm termination.

Other equipment uses a high-impedance loop-through reference input that requires termination at the end of the signal path.

Incorrect termination can affect reference signal amplitude and cause synchronization problems.

HOW TO DISTRIBUTE GENLOCK TO MULTIPLE CAMERAS

In a multi-camera production facility, the synchronization reference may need to reach several cameras, a production switcher, and additional processing equipment.

A common approach is to use a master synchronization generator with multiple reference outputs or a compatible analog reference distribution amplifier.

This allows each device to receive a separate reference connection.

For larger systems, this arrangement is often easier to manage than long chains of loop-through connections.

When planning reference distribution:

• Identify the master synchronization source.
• Confirm the reference format supported by each device.
• Determine how many independent outputs are required.
• Select appropriate 75-ohm coaxial cable assemblies.
• Label each reference connection clearly.
• Confirm the termination method for each signal path.
• Verify reference lock status at the receiving equipment.
• Adjust timing offsets when required by the system design.

Genlock establishes a shared timing relationship, but additional timing adjustments may still be required to align signals correctly at the production switcher.

COMMON GENLOCK TROUBLESHOOTING PROBLEMS

If professional video equipment does not lock to an external reference, several issues should be checked.

1. Incorrect Reference Format

The generator may be outputting black burst while the equipment expects a different supported reference format.

Confirm the signal type and video timing requirements.

2. Incorrect Frame Rate

The reference signal may not be compatible with the equipment's operating frame rate.

Verify the reference and production format settings.

3. Missing or Incorrect Termination

An improperly terminated reference connection can affect signal amplitude and integrity.

Check the equipment's reference input specifications.

4. Damaged BNC Cable

A damaged coaxial cable or unreliable connector can interrupt the reference signal.

Inspect the cable and substitute a known-good assembly when troubleshooting.

5. Incorrect Equipment Settings

Some devices must be configured to use an external reference instead of their internal timing source.

Check the reference selection menu and confirm that the equipment reports a valid lock.

FREQUENTLY ASKED QUESTIONS

What does genlock do?

Genlock synchronizes compatible video equipment to a common timing reference, helping establish consistent timing relationships throughout a production system.

Does genlock carry video?

No. A conventional analog genlock reference provides synchronization timing rather than the camera's program video signal.

What cable is used for genlock?

Professional analog genlock reference connections commonly use 75-ohm coaxial cable with BNC connectors.

Is black burst the same as tri-level sync?

No. Both are analog synchronization references, but they use different waveform structures and are supported by different equipment configurations.

Do all broadcast cameras require genlock?

No. Genlock requirements depend on the camera, production workflow, and receiving equipment. Some systems use internal synchronization or frame synchronizers instead.

Can a 12G-SDI BNC cable carry a genlock reference?

A suitable 75-ohm BNC coaxial assembly can be used for compatible analog reference connections, provided the cable and complete installation meet the equipment manufacturer's requirements. The cable's 12G-SDI rating does not change the reference signal type.

Is genlock the same as timecode?

No. Genlock controls video timing relationships, while timecode identifies positions in recorded or live media timelines. Some systems use both.

THE BOTTOM LINE

Genlock is an important part of many professional broadcast synchronization systems.

Black burst and tri-level sync provide timing references that allow compatible cameras, switchers, routers, and other video equipment to operate together.

Proper reference distribution requires more than connecting equipment with a BNC cable.

Engineers must also consider reference format compatibility, frame rate, cable impedance, termination, and system timing.

Professional 75-ohm coaxial cable assemblies help provide dependable physical connections between compatible reference devices.

Whether you're wiring a television studio, broadcast truck, control room, or live production facility, choosing the right cable construction and connector configuration is an important part of the installation.

AV-Cables — Professional • Reliable • Connected