The frequency of 59Hz has become ubiquitous in modern technology, but where did it come from and why has it stuck around? In this article, we’ll explore the origins of 59Hz, look at why it has persisted over decades, and explain its continued relevance today.
The History of 59Hz
To understand 59Hz, we have to go back to the early days of television broadcasting. In the 1940s, as television was first being introduced in the United States, there was a debate over what the standard frame rate should be. Early TV experiments had used a variety of frame rates ranging from 24 frames per second up to 60 frames per second.
At that time, the electrical power grid in the US operated at 60Hz. This meant that alternating current fluctuated at a rate of 60 cycles per second. If television was to be powered from the same electrical grid, it made sense to match the TV frame rate to this 60Hz supply frequency. Any mismatch between these frequencies could result in visual artifacts like flickering or rolling bands on the TV screen.
So when the National Television System Committee (NTSC) set the standards for black and white TV broadcasting in North America in 1941, they chose a frame rate of 60 fields per second. Actually, due to the way TV scanning works by dividing each frame into two interlaced fields, the field rate is 60Hz while the frame rate is a slightly slower 59.94Hz.
The Interlaced Scan System
Each TV frame is made up of two separate image fields – the odd field and the even field. The odd field contains the odd-numbered scan lines such as lines 1, 3, 5 etc. The even field contains the even-numbered lines 2, 4, 6 etc. Displaying these two fields sequentially creates one complete frame.
This interlaced scan system allowed early TV broadcasts to transmit a 60Hz signal while only having a 30Hz frame rate. Transmitting full 60Hz frames required too much bandwidth for the technology of the 1940s. By interlacing fields, the full image resolution could be attained while matching the 60Hz AC frequency.
Why 59.94Hz?
The NTSC engineers realized that transmitting precisely 60 fields per second was difficult to achieve accurately with clocks of the time. So they settled on a rate slightly slower than 60Hz – 59.94Hz.
This odd standard exists because of the math behind interlacing the two fields:
- Each frame is divided into two interlaced fields
- There are 30 frames per second
- So there must be 60 interlaced fields per second
But to reduce issues with timing accuracy, NTSC made each field take slightly longer than 1/60th of a second. Specifically, each field takes 1/59.94 seconds. So each frame is displayed in 2/59.94 = 1/29.97 seconds. This gives the interlaced field rate of 59.94Hz and the frame rate of 29.97 frames per second.
The Move to Color Television
The next development came in 1953 when color TV broadcasting was introduced. The color television standards had to be compatible with existing black and white televisions. Engineers found that color TV could be accommodated within the existing 59.94Hz system.
The chroma subcarrier frequency, which carries the color information, was chosen to be a factor of the 59.94Hz field rate. Specifically, the subcarrier frequency was set at 227.5 times 59.94Hz which equals 13,565,000 Hz or approximately 14 MHz.
This way, the color subcarrier frequency would periodically align with the black and white video signal, allowing legacy monochrome TVs to receive color transmissions and display them in black and white. So again, the 59.94Hz standard provided the foundation for this compatibility.
Adoption by Video Recording Standards
The 59.94Hz system moved beyond broadcast television into the new field of home video recording that emerged in the 1970s. As video cassette recording allowed home consumers to record TV programs for the first time, the recording standards followed the same 59.94Hz convention:
| Video Standard | Field Rate |
|---|---|
| NTSC VHS | 59.94Hz |
| PAL VHS | 50Hz |
| NTSC Betamax | 59.94Hz |
This ensured compatibility between videotaped recordings and broadcast television. Again, 59.94Hz provided the continuity between home video and over-the-air TV transmissions.
Persistence in Digital Video
Even as television broadcasting evolved from analog to digital, the 59.94Hz rate persisted. Early digital standard definition video formats such as DV and DVD maintained the 59.94 fields per second rate. When high definition (HD) television was introduced, there were new digital video standards to support it but again 59.94Hz formed the backbone:
| Video Standard | Field Rate |
|---|---|
| ATSC HD (North America) | 59.94Hz |
| DVB HD (Europe) | 50Hz |
And even as internet video streaming became popular in the 2000s, formats like 720p and 1080p HD video on YouTube and other streaming services retained the traditional 59.94Hz rate.
Backward Compatibility
This persistence of 59.94Hz comes down to backward compatibility. Once the interlaced 59.94Hz standard took hold in the early days of television, it became advantageous to continue using it as newer video technologies emerged. This allowed content creators to produce new types of video content while retaining compatibility with existing TVs and monitors.
For example, an HDTV broadcast at 1080i/59.94Hz can be displayed on older standard definition TVs because it contains 59.94Hz fields that align with the old NTSC scanning rate. And videos produced for the web at 720p/59.94Hz can be played properly on televisions due to the matching field rate.
Advantages of 59.94Hz Today
While much newer display technology like computer monitors and smartphones now use progressive scanning and refresh rates like 60Hz, 59.94Hz continues to power a lot of major video formats. Here are some of the advantages it still provides today:
Avoids 60Hz Flicker
If video was transmitted at a precisely 60Hz field rate, it could cause annoying flicker on many screens. The slight slowdown to 59.94Hz helps avoid this issue and provides smoother motion rendering.
Supports Film Content
Most films are shot at 24 frames per second. Displaying this at 60Hz would require telecine judder techniques. But at 59.94Hz, the 24fps film content can be displayed cleanly in a 2:3 pulldown cadence.
Consistency with Broadcasting
Modern HDTV broadcasting still uses 59.94Hz for 1080i signals. Keeping internet and disc videos at 59.94Hz ensures they match the field rate of interlaced TV broadcasts.
59.94Hz in Media Production
In the world of video production, 59.94Hz remains the standard frame rate for projects targeting broadcast or home viewing. It offers the right balance between motion quality, compatibility, and bandwidth efficiency. Some key factors include:
- NTSC legacy – it still aligns with the scan rates used by NTSC TV systems
- Interlacing support – 59.94Hz can be interlaced into 60i format for broadcast
- Film content – as mentioned 24fps film transfers cleanly at 59.94Hz
- Downconversion – 59.94Hz allows easy downconversion from 60fps sources
- Standard adoption – all major video editing and production suites use 59.94Hz
For these reasons, professionals working in video, TV, and film choose frame rates based on 59.94Hz like 29.97fps and 23.976fps when authoring content.
59.94Hz in Different Versions
There are a few slight variations of 59.94Hz used in broadcast and production:
- 59.94i – interlaced video at 59.94 fields per second
- 29.97p – progressive scan video at 29.97 frames per second
- 23.976p – film frame rate converted to NTSC video
But all these formats have 59.94Hz as the underlying scanning frequency.
Conclusion
While not a nice round number, 59.94Hz has become engrained in television technology over decades of evolution in video broadcasting and production. What began as a technical measure to accommodate TV’s interlaced scanning in the 1940s went on to be adopted by color TV, home video, HDTV, and internet streaming.
Even as display refresh rates move towards 60Hz and 120Hz, the legacy of 59.94Hz persists in video content itself. It provides continuity between old analog formats and new digital media. So don’t expect 59.94Hz to disappear any time soon – it’s likely to remain a standard for years to come.