Film-Tech Forum ARCHIVE: CAT5/6 for 4xAES

This is topic CAT5/6 for 4xAES in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=16;t=000690

Posted by Dave Macaulay (Member # 813) on 12-02-2010, 03:41 PM:

The Doremi integrated media block (mounted in the DC projector in place of the input card) used with their ShowVault server has two RJ-45 jacks for AES audio output, and a dongle with two RJ-45s to a DB25-M for the input to their D/A converter. There is nothing in the dongle except jumper wires - no transformers or such. I used one CAT6 cable - 25 feet - to connect the IMB and D/A (the second one would be for AES signals #5-8, not currently needed). It worked fine. Doremi does not provide cable, just the dongle. I also tried CAT5 with no difference but used CAT6 just figuring the shield would be good.
So... why should I pay for $$$ AES cable if sending it over CAT5/6 works fine?

Posted by Steve Guttag (Member # 268) on 12-02-2010, 04:38 PM:

I've been doing research on this topic actually. Cat5 does indeed fall somewhat within the AES spec. It is 100-Ohm cable...however its values are all over the place as it flexes. Can it be used...yes. I'm also seeing that on the IMBs of the future that it will gain in prominence.

Cat 6 has proven to be less desirable than Cat 5 on longer runs. But better yet, Belden and others have Skew-Free Cat 5 that is also 100-Ohm cable (note 110-Ohm, is ideal) that will work even better as there will not be timing issues (particularly on longer runs) and the cost difference is somewhat minimal. Often the Jacket color is unique on the Skew-Free version (For Belden, it is maroon to make it quickly identifiable).

You mentioned Cat 6 being shielded. Cat 6 does not have a shield in its spec. All of the Cat cables can have a shield...(aka STP cables instead of UTP cables). That is another issue with using Cat 5 cables for AES...the noise factor...with proper AES cable, each pair is shielded...not only to reject noise from getting in but also to keep its noise confined rather than impressing onto other cables running nearby.

One thing that has me concerned about using Cat 5 cables with RJ45 connectors is...what if an AES cable gets plugged into an Ethernet port on a device? Has anyone tested for damage on that? AES3 can run at rather high levels. Using a unique jacket color will help identify it as a different sort of cable.

-Steve

Posted by Carsten Kurz (Member # 5396) on 12-02-2010, 08:28 PM:

As far as I know, AES is usually transformerbalanced on both sides, ethernet has tolerable voltages of 2V-10V. I would think that the risk is minimal.

CAT5 and CAT6 have 100ohms, so, even without shield, they are okay for AES over decent distances.

I never had any issues sending symmetrical signals over CAT5/6/7, be it analog audio with line and mic levels, AES, DMX, 422, etc.

I usually do prefer SF/FTP though.

Special colors, yes, we get black, orange, lilac, etc here.

- Carsten

Posted by Harold Hallikainen (Member # 5405) on 12-07-2010, 10:44 PM:

European Broadcasting Union 3250E - AES/EBU Interface, Third Edition, 2004. States AEA/EBU may be carried over CAT5 cable for 400 meters unequalized and 800 meters equalized.

The USL JSD-100 has both RJ-45 and DB25 connectors for the AES audio inputs.

Harold