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View Full Version : Digital OUT encoding on TP, now AES & S/PDIF together



your momo
2010-07-16, 08:09
Playing with some external DAC on my TP I noticed that since SBS 7.5.0 both encoding are allways enabled no matter what setting is made in the server.

I could use S/PDIF(BNC) or AES-EBU (XLR) and listen to very good sound without having to change SBS settings...

If I good remember, this "feature" was not working in the past SBS.
Is this normal or is it a bug ?

richardw
2010-07-16, 09:35
Where do you see this? Looking in settings, player, audio, digital output encoding mine is set to aes/ebu and I do not see spdif showing up. I never really could tell a difference switching between anyway and always wondered if that setting actually worked.

I don't think seeing both is proper.

your momo
2010-07-17, 04:27
I don't see both in the SBS setting tab, but whatever I set I get valid signal on both AES-EBU (XLR) and S/PDIF (BNC) out.
If I good remember, this was not the fact with previous (<7.5.0) version of server. Original behavior was that depending on the setting in the server digital out signal was available in either S/PDIF or AES-EBU format...
...I'm pretty sure there is a recent change since prior to 7.5.0 I got the well known "Voltage Overload" message on TP screen each time I changed Digital Output encoding format from S/PDIf to AES-EBU.

In summary I'm happy with today behavior, AES & S/PDIF encoding both available together just on different connectors.
I just wonder why this took so long to be implemented and why there is still a setting in the server player audio tab since it seems to have no effect anymore...

garym
2010-07-17, 05:10
Not sure about the changes, but note that the firmware for the transporter has not changed in a while. Mine is still 80, and I'm running SbS 7.5.2.

your momo
2010-07-17, 06:20
Right TP FW is the same for a while now, as fare as I remember last change (80) was with the move on SBS 7.4
But the behavior change I observe now is linked to the move on SBS 7.5

seanadams
2010-07-17, 08:05
This has always been the case. Both outputs are active at all times, while the software setting allows you to choose the data format.

In other words you can send s/pdif data on an AES/EBU electrical connection, or vice versa, and I have never heard of a DAC that won't accept that.

It's quite silly that they are even different data formats in the first place. They just rearranged a few bits in the data structure.

your momo
2010-07-18, 13:55
Thank you Sean for that clarification, hereby I can confirm it works, no matter of the settings, on all the DAC/inputs I have, even with a Toslink connection.

I know AES & S/PDIF are very close data format, but voltage level are also much higher with AES and I imagine that this could lead in saturation of the input, thus not sound on some material, especially on Toslink.

It's amazing, more than 3 years ago I try that with my HT/amplifier DAC connected through Toslink and it was surely not working until I set the digital output encoding back to S/PDIF ...ok it was with SS6.5.x, so I believe TP can only either AES on XLR or S/PDIF on BNC/Coax/Toslink and I keep this believing until recently.

Good to now, so I can avoid to use my Boom on the balcony and now listen direct form my HT/amplifier zone 2 to my outdoor speakers, even while I keep AES data format on my TP.

Anyway I still believe something has changed positively in SBS 7.5 vs 7.4 since I can play back and forth with the digital output data format setting in SBS without to endure the "Over Voltage" message in the TP, thanks for that folks.

seanadams
2010-07-18, 15:34
I know AES & S/PDIF are very close data format, but voltage level are also much higher with AES and I imagine that this could lead in saturation of the input, thus not sound on some material, especially on Toslink.


Indeed, the voltages are completely different. However, they will always be correct on the respective interface - each has its own electronics for the driving circuit. The software setting only controls the contents of the data stream, which is sent to all ports the same.



Good to now, so I can avoid to use my Boom on the balcony and now listen direct form my HT/amplifier zone 2 to my outdoor speakers, even while I keep AES data format on my TP.


Actually for the best signal you should use either of the 75Ω coax outputs. Although TP implements AES/EBU as well as possible, it is a defective specification and its only practical use is to take advantage of microphone cables you might have lying around the studio, which are terrible for this purpose.

your momo
2010-07-19, 02:06
Actually for the best signal you should use either of the 75Ω coax outputs. Although TP implements AES/EBU as well as possible, it is a defective specification and its only practical use is to take advantage of microphone cables you might have lying around the studio, which are terrible for this purpose.

I try many digital out configurations and best result depends on cable type and connected material too.
Currently I made very good experience with the BNC out, but I could not hear clear difference between AES or S/PDIF data format.
On the other end the RCA out provide a less open sound, so for coax I stay on the BNC ...maybe it's linked to the transformer in the BNC line ?

Phil Leigh
2010-07-19, 10:06
Indeed, the voltages are completely different. However, they will always be correct on the respective interface - each has its own electronics for the driving circuit. The software setting only controls the contents of the data stream, which is sent to all ports the same.



Actually for the best signal you should use either of the 75Ω coax outputs. Although TP implements AES/EBU as well as possible, it is a defective specification and its only practical use is to take advantage of microphone cables you might have lying around the studio, which are terrible for this purpose.

Please make this a sticky!

seanadams
2010-07-19, 11:31
Currently I made very good experience with the BNC out, but I could not hear clear difference between AES or S/PDIF data format.

There isn't supposed to be.

DCtoDaylight
2010-07-19, 16:35
Currently I made very good experience with the BNC out, but I could not hear clear difference between AES or S/PDIF data format.


There isn't supposed to be.

To expand a little on Sean's comment, there is no difference in the signal data transmitted in the AES or S/PDIF format. The only differences are in the extra data, things like copy inhibit and the like. As long as your DAC doesn't totally reject the digital signal (rare with modern digital data receiver chips), there won't be any difference in the sound.

Cheers, Dave

your momo
2010-07-20, 12:36
Thank you all for your valuable inputs.
So if I summarize, AES data encoding through XLR out might be less robust due to usage of none ideal cable HW. So best is to stick on coaxial like RCA or better BNC out with 75 ohm cable.

JohnSwenson
2010-07-20, 16:27
Thank you all for your valuable inputs.
So if I summarize, AES data encoding through XLR out might be less robust due to usage of none ideal cable HW. So best is to stick on coaxial like RCA or better BNC out with 75 ohm cable.

If you use BNC just be sure you get a cable with a real 75ohm BNC connectors. BNCs come in 50 and 75 ohm varieties. Physically they are interchangeable. Unfortunately a very large number of 75 ohm cables with BNCs use 50ohm connectors with 75 ohm cables!!! And its not just companies catering to audiophiles, I see it a lot in the professional video market as well. Companies gush about how high quality their 75 ohm cable is, and then put a 50 ohm connector on it. I don't get it.

Anyway, Blue Jeans Cable is one of the few places that actually uses high quality true 75 ohm BNC connectors on their cables.

John S.

garym
2010-07-20, 17:24
Anyway, Blue Jeans Cable is one of the few places that actually uses high quality true 75 ohm BNC connectors on their cables.

John S.

+1 on Blue Jeans Cable. High quality at a reasonable price....

ar-t
2010-07-23, 10:13
This has always been the case. Both outputs are active at all times, while the software setting allows you to choose the data format.

In other words you can send s/pdif data on an AES/EBU electrical connection, or vice versa, and I have never heard of a DAC that won't accept that.

It's quite silly that they are even different data formats in the first place. They just rearranged a few bits in the data structure.

The only real difference is what the "copy" and "generation" bits are set for. The AES, or "pro" mode, doesn't pass on any copyright info. The "consumer" SPDIF version is supposed to.

As Sean mentioned, they re-arrange what byte this info is contained in. The first 3 (I believe) bytes are different, between the two. Why? Who knows.

Pat

TiredLegs
2010-07-23, 11:55
I don't have anything meaningful to contribute to the topic of this thread, but I just wanted to thank Sean for still participating in these forums. Bravo.

michael123
2010-07-26, 18:42
Thank you all for your valuable inputs.
So if I summarize, AES data encoding through XLR out might be less robust due to usage of none ideal cable HW. So best is to stick on coaxial like RCA or better BNC out with 75 ohm cable.

And I still do not get why XLR cables are worse..
So far, what I learn from lampizator.eu, it is just the opposite - that most of the RCA cables do not provide real 75ohm (and this is impossible to provide it on RCA connectors as I understood) that results in reflections..

In every high-end presentation I attended, shows, only AES/EBU was used (or firewire)..

What are the technical arguments to use RCA over BNC and XLR AES/EBU?
Sure, protocol-wise it is the same.
I am asking with respect to signal handling and mechanism on both sides and cabling

seanadams
2010-07-26, 20:11
What are the technical arguments to use RCA over BNC and XLR AES/EBU?


It's not a medium designed for RF. Low bandwidth, can't transmit a fast slew rate, and doesn't even make an attempt at impedance matching. Slow edge -> jitter. AES/EBU was invented by people who didn't understand s/pdif performance, before the issue was even appreciated by professionals. Professionals like(d) it because it used their favorite analog connector - and don't get me wrong, balanced analog on XLRs is a good thing.

It is true that RCAs aren't proper RF connectors either, but BNCs certainly are, and in either case the correct type of _cable_ is used, and that is critical. RCAs connectors aren't _that_ bad anyway - we manage to run high def component video over them, right?

michael123
2010-07-26, 20:29
It's not a medium designed for RF. Low bandwidth, can't transmit a fast slew rate, and doesn't even make an attempt at impedance matching. Slow edge -> jitter. AES/EBU was invented by people who didn't understand s/pdif performance, before the issue was even appreciated by professionals. Professionals like(d) it because it used their favorite analog connector - and don't get me wrong, balanced analog on XLRs is a good thing.

It is true that RCAs aren't proper RF connectors either, but BNCs certainly are, and in either case the correct type of _cable_ is used, and that is critical. RCAs connectors aren't _that_ bad anyway - we manage to run high def component video over them, right?

thanks!
now you can make this sticky :)

JohnSwenson
2010-07-27, 15:22
Another pet peave of mine with AES/EBU is the voltage level, its supposed to use 3-5V. Do the math on 3-5V into 110 ohm and you get about 30mA minimum that the transmitter has to try and dump into the cable, with fast squarewaves. This causes large voltage spikes on the power and ground planes in the source. If things are not done just right that noise winds up in the transmitter circuits, clock circuits, reclocking circuits etc. Its very difficult to build a circuit that is not impacted by this.

Look at all modern high speed interfaces where jitter is critical, NONE of them use such high voltages, its almost impossible to preserve low jitter with such high voltages.

S/PDIF on the other hand uses 0.5V across 75 ohms, which is MUCH better, about 7mA.

John S.

michael123
2010-07-27, 18:13
Intuitively, I thought that higher voltage means better noise rejection..
How do you explain that the XLR wire has limited bandwidth compared to coax?

BTW, is there transformer coupled output of AES/EBU in Transporter, right?
I was told that transformer makes the cable less relevant..or I was misinformed?

Phil Leigh
2010-07-27, 23:40
Intuitively, I thought that higher voltage means better noise rejection..

For analogue audio signals, higher voltage levels usually (but now always) result in better signal-noise ratio. However the problem with digital signals is that they are RF square waves (nothing like normal audio signals) and to deliver perfect high frequency square waves at higher voltages/currents requires high slew rate circuitry and puts more strain on the power supply and driver circuits of the transmitter. This cause the problems John describes.




How do you explain that the XLR wire has limited bandwidth compared to coax?


Bandwidth is in part constrained by the accuracy of impedance matching of the transmission line. The XLR plugs and sockets do not provide an accurate impedance match and the AES/EBU standard has changed over time.

Coax + good (expensive) plugs/sockets such as Canare are a little better but 75-ohm BNC + 75-ohm cable is the best approach.

see here: http://broadcastengineering.com/mag/broadcasting_aesebu_digital_audio/

JohnSwenson
2010-07-28, 00:43
BTW, is there transformer coupled output of AES/EBU in Transporter, right?
I was told that transformer makes the cable less relevant..or I was misinformed?

Transformers block DC between boxes, thus getting rid of low frequency ground loops. This can significantly improve sound in many circumstances.

They do NOT improve impedance matching in most cases. Wide bandwidth pulse transformers are definitely a black art, getting them right is an exceedingly difficult task, the upshot is that almost all implementations with transformers will be worse RF wise than without them. But people put them in because of the ground loop breaking properties. In most cases its a worthwhile trade off.

There might be a case where a transformer just happens to improve things. The whole field is so bad with transmitters, cables and receivers being all over the map with almost none of them actually matching the standard. Given this it is actually possible that a given non perfect implementation in the transmitter might match another non perfect implementation in a receiver better than something else which more closely matches the standard.

Thats why there are so many different opinions about what is a good source, one which very closely matches the standard may actually perform worse than one very far from the standard when driving a receiver which is also far from the standard.

John S.

Andy8421
2010-07-28, 05:07
Just for a bit of historical perspective, the AES/EBU spec was designed so that digital audio could be handled in a studio environment just as if it was analogue. So not just mic cables, but patch panels and permanent wiring could all cary the 'new' digital audio. This really mattered if you were a legacy broadcaster and had a significant investment in studio infrastructure. As has been pointed out elsewhere, the AES/EBU spec is not 'better' than S/PDIF, it was designed for a different purpose.

Andy.

pfarrell
2010-07-28, 05:14
On 07/28/2010 08:07 AM, Andy8421 wrote:
> Just for a bit of historical perspective, the AES/EBU spec was designed
> so that digital audio could be handled in a studio environment just as
> if it was analogue. So not just mic cables, but patch panels and
> permanent wiring could all cary the 'new' digital audio.

For sure, and putting a digital signal through a TT patch panel is going
to do wonderful things to the wave forms.



--
Pat Farrell
http://www.pfarrell.com/

JohnSwenson
2010-07-28, 14:00
For sure, and putting a digital signal through a TT patch panel is going
to do wonderful things to the wave forms.

--
Pat Farrell
http://www.pfarrell.com/

And thats one of the reasons such high voltages were used, to make sure there was SOME semblance of a signal left over after going through such highly non optimal wiring.

John S.

ar-t
2010-07-30, 14:40
In case anyone cares..............here is a link to the App Note, that shows the differences between the Channel Status block, between AES/EBU (Pro) and SPDIF (Consumer) modes.

http://www.cirrus.com/en/pubs/appNote/an22.pdf

Pat

ar-t
2010-07-30, 14:47
Another pet peave of mine with AES/EBU is the voltage level, its supposed to use 3-5V. Do the math on 3-5V into 110 ohm and you get about 30mA minimum that the transmitter has to try and dump into the cable, with fast squarewaves. This causes large voltage spikes on the power and ground planes in the source. If things are not done just right that noise winds up in the transmitter circuits, clock circuits, reclocking circuits etc. Its very difficult to build a circuit that is not impacted by this.

John S.

May be difficult, but not impossible. But, judging by the level of competency I see in a lot of stuff, it sure seems that way. Like.........well, I won't say who, but it is some schlock the DIYers love to futz with (and is not made by the good people who allow us to post on their forum), it is a good example of what happens when you copy the App Note, and the junior engineer who wrote it is an idiot.

Anyway, if you try sticking that circuit directly on the output of the typical TX chip, with one ground pin, you are probably asking for trouble. Which, you deserve.

Pat

ar-t
2010-07-30, 14:58
Transformers block DC between boxes, thus getting rid of low frequency ground loops. This can significantly improve sound in many circumstances.

They do NOT improve impedance matching in most cases. Wide bandwidth pulse transformers are definitely a black art, getting them right is an exceedingly difficult task, the upshot is that almost all implementations with transformers will be worse RF wise than without them. But people put them in because of the ground loop breaking properties. In most cases its a worthwhile trade off.

There might be a case where a transformer just happens to improve things. The whole field is so bad with transmitters, cables and receivers being all over the map with almost none of them actually matching the standard. Given this it is actually possible that a given non perfect implementation in the transmitter might match another non perfect implementation in a receiver better than something else which more closely matches the standard.

Thats why there are so many different opinions about what is a good source, one which very closely matches the standard may actually perform worse than one very far from the standard when driving a receiver which is also far from the standard.

John S.

Once again, if you copy the App Note, you get what you deserve. Most transformer circuits do make things worse. Poor impedance control. Excessive LF cut-off, which is not good for a data stream that has a varying duty cycle (as SPDIF does).

(As duty cycle changes, you get changes in DC offset. Which, moves the decision point up and down, if the cut-off is too high.)

(I won't mention which brand is the worst, in this regard. Contrary to the claims of the guys who make them.)

A poorly implemented one does break up ground loops, but at the expense of other problems. Good designs are not that common.

Pat

michael123
2010-07-31, 05:22
How would you evaluate Transporter from the quality of its implementation of BNC and XLR digital ins/outs?
Which ones implement this better? Why?
Interesting to hear your judgments from pure technical point of view..