Limiters on AES inputs

[glenn]

Maybe I need a little education on this so I think it is time to pose a question.

 

Why would a limiter or compressor ever be needed on a AES mixer input?

 

If audio is clipped at a point in the signal chain and then converted to AES,  there is no way of repairing the clipping distortion with a limiter or compressor that is receiving the AES signal. Yes you could reduce the amplitude of the distorted signal but if the signal is distorted coming into a mixer and there is data missing then it can not be fixed in the AES input of a mixer.

 

AES has a dynamic range of 144dB so it can easily transport any audio signal that is encoded onto it. If the audio contained in the AES stream has technical problems the only place to properly fix it is in the device that has generated the AES signal not down stream from that place.

 

 

 

Are people working with AES in a different way than I think they are as to require the use of a limiter on an AES input?

 

Thanks

 

Glenn

 

 

[PTA]

Maybe I need a little education on this so I think it is time to pose a question.

 

Why would a limiter or compressor ever be needed on a AES mixer input?

 

If audio is clipped at a point in the signal chain and then converted to AES,  there is no way of repairing the clipping distortion with a limiter or compressor that is receiving the AES signal. Yes you could reduce the amplitude of the distorted signal but if the signal is distorted coming into a mixer and there is data missing then it can not be fixed in the AES input of a mixer.

 

AES has a dynamic range of 144dB so it can easily transport any audio signal that is encoded onto it. If the audio contained in the AES stream has technical problems the only place to properly fix it is in the device that has generated the AES signal not down stream from that place.

 

 

 

Are people working with AES in a different way than I think they are as to require the use of a limiter on an AES input?

 

Thanks

 

Glenn

Hi Glenn,

 

I think Rado might be referring to the fact that on Nomad, there is now the option with the AES input to have adjustable digital gain with the auto trim feature. So I believe that if you are using it in this way on Nomad, you can have the input signal from your receiver and an added digital gain by way of the autotrim, giving you a signal that could clip. Does that make sense?

[Matt Martin]

Hi Glenn,

 

I think Rado might be referring to the fact that on Nomad, there is now the option with the AES input to have adjustable digital gain with the auto trim feature. So I believe that if you are using it in this way on Nomad, you can have the input signal from your receiver and an added digital gain by way of the autotrim, giving you a signal that could clip. Does that make sense?

Yes exactly. A few times a day I'll check my AES input levels and realize that my AES inputs got bumped up (or down) a few dB above 0 due to autotrim. I like to have autotrim enabled for my analog sources, but in my opinion autotrim for my AES Zaxcom wireless channels should effect the Zaxnet gain and not the digital input gain. If this were the case, and AES input gain would stay at 0, then yes, no input limiter would be needed, because as you say Glenn, the audio would clip at the TX first. But currently there is certainly a way to accidentally clip the AES input at the mixer end and not necessarily at the TX. In this case an input limiter would be a good safety feature to have.

 

However, I'd be much happier to have the option for autotrim to affect the Zaxnet gain and forget about input limiters But I believe one or the other is needed.

[pindrop]

Probably not limiters for the input as such but for where gain has been added in the AES signal chain to disk, where there's limited post production resources perhaps, a limiter to disk might be useful if that gain has been added to the input and things then get hotter than expected.

For example gain might be added to the input for hotter levels to disk to save those 'why are your levels so low' calls, but then there could be a danger of the unexpected overloading the disk headroom.

[John Blankenship]

Maybe we could rename this thread, "How to eliminate the positive attributes of a digital connection."

[rich]

i run my QRX into my 788 via AES, and, as PalmerT says, i add a bit of gain at the 788 because this means that i am not as close to the limiter on my transmitter as i am at the recorder, which gives me a bit of headroom when levels unexpectedly change. and it is quicker to change gain on my 788 than on the transmitters.

 

i am not interested in using the AES inputs to maintain a purity of digital signal per se. more that it is much more convenient - it makes the bag lighter because i loose 4 XLR connectors, and also leaves the input XLR's and TA3's free should i need to swap anything over.

 

personally, i think things in our world are too unpredictable to be setting the gain for AES inputs at 0dB and then tweaking gain at the transmitter.

[RadoStefanov]

Hi Glenn,

 

I think Rado might be referring to the fact that on Nomad, there is now the option with the AES input to have adjustable digital gain with the auto trim feature. So I believe that if you are using it in this way on Nomad, you can have the input signal from your receiver and an added digital gain by way of the autotrim, giving you a signal that could clip. Does that make sense?

Palmer got it exactly right. 

Also important to mention that fast transient clipping inserts a moment of silence when going over 0. It sounds distracting.I prefer to have constant distorted sound instead of short silence. 

My mixing situation is requiring me to sustain good level around -15 with peaks around -12 post fader  because what I track in my recorder ends on TV. NO POST. It can go from bike engine to whispering. Having the gain in one spot and using the fader is not an option for me. I also control the transmitter gain to stay in a sweat spot altogether.

At the end of day I experience strange undesired affect when AES input is overloaded.

And the need for limiters on the AES is not something that just popped out. Limiters and LCF  have been requested over and over again.

 

I understand that Zaxcom innovates and constantly adds more and more features based on my and many other people's request.

I am immensely grateful for it. But...

[RPSharman]

The field is a very unusual place, and we sometimes have to do things which don't "make sense" in order to achieve results which might not be ideal, but are the best possible results given the circumstances.

Most of our manufactures are guilty of telling us how we should be using our gear, or build things in a way that makes sense to them as engineers, but don't allow the flexibility we need in the field.

There are certainly limitations when using wireless (any wireless), so some sacrifice is going to be made to quality, as in Rado's situation. If a feature can be added to lessen the compromise, then it's fair for him to ask for it.

Zaxcom is full of great features that might never need to be used. It's the major selling point. But when you need that feature, you really need it.

[Bash]

The scenario that immediately occurs to me is the one where I am mixing a bunch of IPs, analogue and or digital. I may well be doing a small amount of processing to the (say) analogue mics, and |I may well wish to do similar processing to the digital mics. So, for instance, I often do a little bit of compression to my incoming mic sources, not so much as over level protection, but more as a way of slightly beefing up the dialogues. More so if I know that there is to be little or no post production, track lay, or dubbing involved down the line.

 

Kindest,

 

sb

[ramallo]

+1 Glenn,

 

I don't understand what is the need of a limiter on a AES. If any clip occurs before this limiter (anywhere in the digital chain), this signal will be broken, the limiter isn't a cure. The limiter must be before the digital chain.

 

In other hand, if you want to control the dinamic of the source, much better do on postpo

[VASI]

From what I understand the users need the limiters on AES signal in the mixer side due:

 

You can have undistorted sound in the first chain of signal (digital microphone or digital transmitter), but you can distort the signal on the mixer side.

 

I can feel Rado about for no post production.

[glenn]

Thanks to all. I now have a better understanding of where we are and how we got here.

 

Glenn

[RadoStefanov]

Proposed this last April when Glenn and Howy came to visit me on set.

Still not a perfect solution because of the small delay when changing TX gain. In the fact I am very conservative with the TX gain. The TX card recording is my pre fader just in case.

 

 

Howecver, I'd be much happier to have the option for autotrim to affect the Zaxnet gain and forget about input limiters But I believe one or the other is needed.

[RadoStefanov]

 

+1 Glenn,

 

I don't understand what is the need of a limiter on a AES. If any clip occurs before this limiter (anywhere in the digital chain), this signal will be broken, the limiter isn't a cure. The limiter must be before the digital chain.

 

In other hand, if you want to control the dinamic of the source, much better do on postpo

 

It was explained that the the modulation occurs when raising the digital gain in Nomad or Maxx.

But I agree in normal situation with even small amount of post production I can maybe avoid clipping.

[RadoStefanov]

Thanks to all. I now have a better understanding of where we are and how we got here.

 

Glenn

Sorry for not being available to take your call last four days. My heavy schedule and the time difference prevented me from picking up.

[ramallo]

It was explained that the the modulation occurs when raising the digital gain in Nomad or Maxx.

But I agree in normal situation with even small amount of post production I can maybe avoid clipping.

 

But you can only avoid the clipping in the analog domain (For example in the analog part of your TRX), if any clips occur on digital domain is not possible solve it.

[RadoStefanov]

But you can only avoid the clipping in the analog domain (For example in the analog part of your TRX), if any clips occur on digital domain is not possible solve it.

There is no clipping in the analog to digital conversion in the TX so the wireless is sending clean signal to qrx. Qrx is sending same clean signal to Nomad. Nomad has a digital gain adjustment that performs similar to analog gain.

[Michael Wynne]

I think the answer is it depends on the application. For one complex live filming I use the digital input limiters on the 788t which is being fed AES out from a digital out card of a Yamaha 01v because the channel strip processing is being utilized for the live sound portion and the program audio content is being recorded separate so it's pre fade / eq out and this particular product doesn't get a proper audio post mix, so the use of these digital limiters limit the dynamic range when done tastefully and further level the program audio for final release.


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[ramallo]

There is no clipping in the analog to digital conversion in the TX so the wireless is sending clean signal to qrx. Qrx is sending same clean signal to Nomad. Nomad has a digital gain adjustment that performs similar to analog gain.

 

This is very different (isn't AES/EBU). I presume that the Nomad have a 32 bit (float) mixer and a limiter on the Nomad mixer makes sense.

[studiomprd]

ramillo: " I presume... "
why ?

[ramallo]

ramillo: " I presume... "

why ?

Because is the usual in 2014 (and 5 years ago too), easy for programing (float instead fixed) (Less rounded errors), (better for digital mixers). In your sophist way, why not?

[RadoStefanov]

Romilo,

dont pay attention to the noise.

no need to answer stupid questions...

[pindrop]

John Blankenship, on 03 Sept 2014 - 03:24 AM, said:

Maybe we could rename this thread, "How to eliminate the positive attributes of a digital connection."

Rename away but there are other reasons for using AES ins like a Schoeps Super CMIT, for which I'd like to have a safety limiter and HP filter, but at present go in analog with a DA42 to get that, much less convenient than AES42 direct.

[John Blankenship]

John Blankenship, on 03 Sept 2014 - 03:24 AM, said:

Maybe we could rename this thread, "How to eliminate the positive attributes of a digital connection."

Rename away but there are other reasons for using AES ins like a Schoeps Super CMIT, for which I'd like to have a safety limiter and HP filter, but at present go in analog with a DA42 to get that, much less convenient than AES42 direct.

Good point.