<p>Wikipedia does <a href="https://en.wikipedia.org/wiki/SMPTE_424M" rel="nofollow">mention</a> it - with a reference <a href="https://tech.ebu.ch/docs/techreports/tr002.pdf" rel="nofollow">link</a> included:</p>

<blockquote>
  <p>Within this standard there are three formats known as Level A, Level B
  Dual Link (B-DL) and Level B Dual Stream (B-DS). The Level A format is
  the direct mapping of uncompressed 1080p (up to 60 fps) video into a
  serial digital interface at the nominal 3 Gbit/s. The Level B-DL
  format is the mapping of dual-link HD-SDI/SMPTE 372M (i.e.: 1080p up
  to 60 fps) in a single serial digital interface at the nominal 3
  Gbit/s. The Level B-DS format is the dual-stream carriage of two
  independent HD-SDI/SMPTE 292M signals (720p up to 60 fps or
  1080i/1080p up to 30 fps) in a single serial digital interface at the
  nominal 3 Gbit/s</p>
</blockquote>

<p>The PDF reference has the descriptions starting on pg. 17.</p>

CC BY-SA 3.0
2016-04-27T05:35:41.637Z
2016-04-27T05:35:41.637Z
Gyan
<p>Can someone point me at a description of the difference between a 3G-A SDI signal and a 3G-B SDI signal.  </p>

<p>I have a rack with a BlackMagic ATEM 2 M/E Production Studio 4K and a bank of 3 SWT Pro-HD monitors.  The ATEM is set up to run 1080p59.94. The monitors show "No-sync" when fed from the Aux outputs of the ATEM.</p>

<p>If I insert a Decimator MD-HX between the Aux output and the monitor's SDI input, it shows the SDI input to the MD-HX running 3G-B 1920x1080p59.94.
The SDI output of the MD-HX is switchable between 3G-A SDI and 3G-B SDI. Switching he output to 3G-A makes the signal appear on the monitor.</p>

<p>The problem does not appear if I run the ATEM at 720p59.94.</p>

<p>Wikipedia's article on SDI does not mention the A and B variants of SDI.</p>

<sdi>
What's the difference between 3G-A SDI and 3G-B SDI?
Richard Milewski
# What's the difference between 3G-A SDI and 3G-B SDI?

(Asked by: username_0 on 2016-04-27)

Can someone point me at a description of the difference between a 3G-A SDI signal and a 3G-B SDI signal.

I have a rack with a BlackMagic ATEM 2 M/E Production Studio 4K and a bank of 3 SWT Pro-HD monitors. The ATEM is set up to run 1080p59.94. The monitors show "No-sync" when fed from the Aux outputs of the ATEM.

If I insert a Decimator MD-HX between the Aux output and the monitor's SDI input, it shows the SDI input to the MD-HX running 3G-B 1920x1080p59.94.
The SDI output of the MD-HX is switchable between 3G-A SDI and 3G-B SDI. Switching he output to 3G-A makes the signal appear on the monitor.

The problem does not appear if I run the ATEM at 720p59.94.

Wikipedia's article on SDI does not mention the A and B variants of SDI.

**Tags:** sdi


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## 1 answers

### Answer by username_1 on 2016-04-27. Score: 3 | Accepted answer

Wikipedia does [mention](https://en.wikipedia.org/wiki/SMPTE_424M) it - with a reference [link](https://tech.ebu.ch/docs/techreports/tr002.pdf) included:

> Within this standard there are three formats known as Level A, Level B
> Dual Link (B-DL) and Level B Dual Stream (B-DS). The Level A format is
> the direct mapping of uncompressed 1080p (up to 60 fps) video into a
> serial digital interface at the nominal 3 Gbit/s. The Level B-DL
> format is the mapping of dual-link HD-SDI/SMPTE 372M (i.e.: 1080p up
> to 60 fps) in a single serial digital interface at the nominal 3
> Gbit/s. The Level B-DS format is the dual-stream carriage of two
> independent HD-SDI/SMPTE 292M signals (720p up to 60 fps or
> 1080i/1080p up to 30 fps) in a single serial digital interface at the
> nominal 3 Gbit/s

The PDF reference has the descriptions starting on pg. 17.


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