AES/EBU Digital out loss in output level

[The WizzardParticipant]

Hi everyone,

I hooked up my SQ 6 (actual firmware 1.4.1) via AES digital out to an iNova IN380 PA System.
If I feed the PA with 0dB unity gain from the A&H and compare this to an analog mixer connected to the PA with 0dB I get a loss in level from the SQ6 to the PA of about 14 dB.
Same when I changed the cables (both are 110 Ohm) or when I connect the SQ to my DAW interface via AES compared to analogue.

This makes me sad. This happens with SQ 6 AES output sample rate at 44,1 KHz or 96 Khz…

Any idea?

Thanx in advance 🙂

Greez from GErmany (please excuse my chaotic English writing)

Stephan

[Nicole A&HModerator]

Hi Stephen,

Please can you log a ticket with product support so I can investigate this further for you?

https://support.allen-heath.com/

Kindest Regards,

Nicole

[New2SQParticipant]

It might just be a characteristic of the board. When I Record to USB on the SQ-Drive(Stereo) and import the file into Audacity, I see the same thing. The board shows 0 but Audacity shows about a 15 dB drop. I thought maybe it’s because the SQ has a lot of head room above 0 until it peaks.

[Nicole A&HModerator]

Hi Stephan,

I have had a brief look at this for you without a ticket being logged.

After looking at the specs of the PA system you are using and testing the local AES output of an SQ into an AES input rack (to simulate your AES input on your speaker), it looks like you are possibly having some attenuation issues with the AES input on the speaker system. All signals on the SQ AES outputs and the AES inputs rack were the same level and were clean with no issues.

If you are swapping from trying an AES input to then trying an analogue input on your speaker, then these will be being processed differently. This could explain why you are seeing a difference in output level as the AES inputs will be using DSP, but the analogue will not. I would suggest investigating the AES inputs on your PA system first.

However as I mentioned before, please feel free to log a ticket with us in product support and we will be happy to assist you further.

Kindest Regards,
Nicole

[The WizzardParticipant]

Hi Nicole,

first of all: it is amazing that you take care so quickly. I am glad being in the A&H SQ fandom 🙂

Regarding my PA System: It processes the digital inputs and the analog inputs thru the same DSP. In fact, I can switch on the fly between AES/EBU and ANALOG input. So I do not believe that is the problem with the PA.
Another fact is the following:
With the SQ6 mixer connected via AES/EBU to my soundcard it is the same drop of 14 to 15 dB…
Are there different Standards of AES/EBU specifications with different pp voltages or different 0dB levels?

Thank you so much for your support! I will log a ticket now. I knoq this things ( I am an IT guy who did a lot of support and without tickets you bust 😉

Cheerio and tajke care 🙂

Stephan

[The WizzardParticipant]

Hi New2SQ

I will test this. Interesting point. I come back with my results. THX

[peterlandersParticipant]

Maybe I’m completely out to lunch on this, but my understanding was that, in the digital realm, 0dB is where clipping happens; as indicated in DAWs, that’s generally the top of the meter. You’re setting safe record levels at around -12 dB.

On a digital mixer, I’m wondering if it’s the same thing – but the faders still use analog-style labels? Thus, 0dB on the fader is your good, safe place with plenty of headroom, but it corresponds digitally outside the mixer with -12 dB, give or take?

In other words, it’s not attenuating anything, it’s just a reporting issue?

But I admit I could be entirely wrong…

[FabParticipant]

Don t forget the dbfs alignement and meter calibration in the sq;
+18dBu = 0dBFS
0dB meter = -18dBFS
I don’t know audacity but DAWs generally show their levels in the dbfs scale.

[New2SQParticipant]

@nicolehiggins is there an industry standard, or just manufacture’s preference as to what scale they use?

[The WizzardParticipant]

Hi Peterlanders,

I must say this stuff regarding USB recording an DBFS and DbU can lead to misunterstandigs. What I tried out then was the following (and I opened a ticket at A6H and will post the results of their Research here):

I have a PA System with an AES digital Input and analog XLR Inputs. I hooked up both from SQ6 main XLR Outs and SQ6 AES out.
I played back a song from an iPhone hooked on a Stereo in of the SQ6.
Then I switched AT MY PA-SYSTEM between analog and digital in and had a dramatic drop in loudness Level. I mean, if I drive my PA digitally I loose all the power. This cannot be cause the digital out an in must match.

If I hook up another digital out from another device to my PA, there is no drop between analog and digital in.

[The WizzardParticipant]

Hi FAB:
yes I know but this should not matter. I f I record with my Yamaha digital mixer 01v96 via ADAT into my RME interface I have round Zero on the meter Levels on my mixer AND in Cubase the same.
Zero is Zero, no matter what the device calculates or references with in the Background. I mean the interfacing between the devices must deal with this not the user.
You would get mad seeing on every device another “Zero”…

But thank you for your Statement what makes me think About the exact drop in volume… could be the 18 dB…. it is so weird

[Nicola A&HKeymaster]

Zero is Zero

Not quite. As Fab points out above, you are looking at very different scales. Yamaha mixers display dBFS, same as your DAW or audio interface. So it’s normal you get the same 0 reading.
Meters on Allen & Heath mixers display an analogue scale, with 0dB = -18dBFS. Try measuring a Sig Gen sine wave output reading +18dB on the meters, and you should get 0 on your audio interface.

[Brian78Participant]

Stephan, did you get any more info about your problem? I’m sending an Aux mix out of AES to a Blackmagic switcher via a DA/AD converter. The aux is compressed pretty heavily and the level is +10 to +15 with even an occasional flash of red. However, my converter input level reads really low and I’m only getting -15 to -20 on the switcher. I’m having to gain up the switcher significantly to get a usable signal. The AD/DA converter has a gain adjustment but it’s only for analog input. Digital input is passed through at the same level.

[KeithJ A&HModerator]

@brian78 – As Nic says, When the meters on the desk show 0dB, the AES output will be at -18dBFS (to give 18dB of headroom before clipping).
With the same 0dB on the meters, the analogue outputs will be +4dBu (professional line level).

Of course we can only comment on the A&H side, but these are both industry standards.

Thanks,
Keith.

[StratKatParticipant]

The amount of “headroom” needed above a nominal “0 dB” is not agreed-upon by all designers of equipment and software. These days it is very easy for our digital audio to find its way to digital audio meters which disagree with the A&H meters.

I have run into this same problem recently with webcast equipment at our church. Our console produces a -18dBfs signal (as described by KeithJ above) on the mixer’s AES/EBU connector. This plugs into a device which merges our digital audio with video and formats it into an HDMI connection. The HDMI then feeds a Blackmagic interface to a Windows PC running Wirecast software for webcasting. The audio is digital straight through and no levels are altered.

But when our digital audio reaches Wirecast it is quite low on Wirecast’s audio meters, requiring a LOT of gain using Wirecast’s audio level controls. The explanation for this: Wirecast does not expect to receive audio produced with 18dB of headroom. A lot of video production systems these days seem to only provide about 6dB of headroom above what they call “0 Vu.” So if we create a pure digital path from our professional audio console, we might be making audio that’s about 12dB too low.

And to make matters worse, when discussing the problem with tech support for these manufacturers, they often do not even know what “dBfs” means.

And to top it all off: a lot of the equipment or software we use these days doesn’t even have audio meters.

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