Topic: 744 - Aerco limiting help

[j5brock]

Recorded a show the other night - running dpa 4023 > psp 2 > 744 channels 1 and 2
                                                          mk21 > aerco mp2 > 744 channels 3 and 4

I am including a screen shot of the 4 mono channels in samplitude. I didn't think the 744 had a limiter for channels 3 and 4.. and I don't believe the Aerco has a limiter.. So what could cause this?

Jeff

[easy jim]

That looks like it could be brickwalling, where the Aerco's output levels were too high for the 744's input stage settings. 

I've seen this once before with my Aerco/R-4 Pro combo, when I drove the levels too hard on the Aerco to get good levels on the R-4 Pro. It's probably a good thing to keep in mind that since the Aerco's outputs are unbalanced (-10dBU instead of +4dBU), they output less signal than the PSP2, so you may risk brickwalling when you drive the Aerco harder to get the same output level to a recorder with balanced inputs.  It's better to play it safe and run a little more conservatively.

Where was the gain set on the 744? at 0dB?
How hard were you driving the Aerco to get those levels on the 744? (most have +20dB gain at the 'zero' gain setting)

[JasonSobel]

That looks like it could be brickwalling, where the Aerco's output levels were too high for the 744's input stage settings. 

I agree that it looks like brickwalling, but your description isn't very good.  First of all, the SD 7xx units can handle a +20 dBu signal before clipping (that's with the line-in set to 0dB gain).  I'm not sure what the exact specs for the output signal of the aerco is, but I really doubt that it is that high.  And that's not what brickwalling is.  What might have happened is that the signal from the mk21's was too hot for the aerco, so you were overloading the circuitry in the aerco.  When this happens, the aerco reaches it's limit and then it won't output any hotter signal.  So if you're just watching the digital meters on the 744, you won't see clipping, because the aerco can't output a signal high enough to cause a digital clip.  That's brickwalling.  It's hard to know for sure, because I don't think the aerco has any clip indication lights.  The fix for this type of problem is to either lower the gain on the aerco, or if that is not possible, lower the level of the input signal before it gets to the aerco (so as not to overload the preamp).

edit to add:
how does it sound?  If it doesn't sound too bad, then you weren't overloading the aerco preamp too much.
also, sometimes low batteries can cause pre-amps to overload at lower volumes.  (that's what happens with the sonosax, I'm not sure how the aerco reacts to low battery power).  but maybe the "fix" for this issue in the future is to make sure your batteries are always fresh.

[j5brock]

Fully charged 8000mah dvd battery. running with gain at 30. Same settings for the opener - which was a significantly quiter group. You are correct in that the aerco does not have clip lights.. and this is the first time I have run the schoeps through the aerco - usually run the dpas through it. And the schopes run considerably hotter than the dpas.. Is there a way to tell in the field if I am brickwalling from the aerco - and if not - is my best option to back off 10db and adjust my levels with the 744?  thanks

Jeff

Oh - and the sound is relatively fine - minus the dynamics

[easy jim]

That looks like it could be brickwalling, where the Aerco's output levels were too high for the 744's input stage settings. 

I agree that it looks like brickwalling, but your description isn't very good. 

Thanks for clearing some of that up...I was definitely a little garbled in my attempted post above.  Doh...need more coffee...

I doubt the schoeps would have overloaded the aerco, although the possibility that low batteries might have caused it to overload at lower gain settings is certainly an interesting possibility - especially considering the high powering requirements for schoeps.  I've also heard/seen that from a sonosax/schoeps source where the batteries died during the show.  Maybe if the schoeps do run a lot hotter than the DPAs, you'll need to keep the gain setting lower on the aerco b/c the schoeps' output signal might overload the aerco's circuitry at higher gain settings when recording louder music.

I would not be surprised, however, if the aerco could output a signal hotter than +20dBu.  I've managed to clip the signal I sent from it to the balanced inputs of other devices and an interface that were all able to accept up to +19dBu.

The fix for this type of problem is to either lower the gain on the aerco, or if that is not possible, lower the level of the input signal before it gets to the aerco (so as not to overload the preamp)....

how does it sound?  If it doesn't sound too bad, then you weren't overloading the aerco preamp too much.

Good suggestions...when I've experienced this, I always just turned the gain down some on the aerco and everything was fine.  If the schoeps do indeed output a signal high enough to overload the aerco's circuitry, I guess you'd need some inline attenuators to run in front of the pre.

[bgalizio]

As far as Aerco clipping goes, I have this e-mail from Jerry Chamkis:

The AERCO clips at about +24 dBM which in the special case of a standard (600
Ohm) load is the same as dBv. Since the preamp can drive a 600 ohm load with
~0 loss of signal (low output impedance), the dBU (unloaded output)
is the same.

[j5brock]

I understand where you guys are coming from. But from a real world field recording of loud music - as far as I can determine - setting levels on the Aerco will be based on past experience (read failures and successes) rather than a known quantifiable setting. Granted - I know the sensitivity of the mics - but unless I know the strength of the PA signal hitting the mics at a particular known spot in a venue.. I can only guess at the gain setting. Or am I missing something?
Jeff

[easy jim]

You're right that you'll have to just guess at a show Jeff.  If pairing the aerco with schoeps, it sounds like you're going to want to stick with lower gain settings (maybe +20dB) and then adjust downstream either on the 744 at the show or in post-production when you edit the recording.

As far as Aerco clipping goes, I have this e-mail from Jerry Chamkis:

The AERCO clips at about +24 dBM which in the special case of a standard (600
Ohm) load is the same as dBv. Since the preamp can drive a 600 ohm load with
~0 loss of signal (low output impedance), the dBU (unloaded output)
is the same.

Interesting...