Built-in limiter?

[Beeblebrox]

Anyone know if the DVX has a built-in limiter? If so, can it be turned off?

[Barry_S]

Yes the DVX has a limiter, and yes it can be turned off using the menus. *Generally, I'd recommend keeping the limiter turned on--it only kicks in when you get close to distortion levels. *A limiter shouldn't be confused with an AGC (auto gain control) circuit which kicks up low voltage signals (raising your noise floor) and attenuates higher voltage input signals--a recipe for bad sound recording. Confusingly, AGC is sometimes referred to as ALC (auto level control). Equally confusing is the fact that Panasonic refers to the DVX100's limiter circuit as ALC. They should just call it a limiter, period.

[Barry_Green]

Except that that post makes the whole situation a little confusing, because the DVX calls its limiter an ALC... which I believe they call an auto limiting circuit...

The volume pumping circuit is also frequently called AGC for automatic gain control.

In any case, the DVX has the good one, not the bad one.

[Barry_S]

Ahh, while I was editing my post, Barry has jumped in with a clear explanation. How's V2 Barry?

[Beeblebrox]

Awesome. Thanks for all the info.

[Barry_Green]

Perfect as always! Your posts are some of the most valuable reading on this board. Sorry I horned in there, just wanted to make sure that when people read the menus and saw "ALC", they didn't panic... ;)

[Barry_S]

Barry, your comments are always appreciated. *I try to be thorough and clear, but don't always succeed. *I never claim to be definitive--that's for sure :-). *I'm constantly learning from everyone's contributions and appreciate different perspectives and approaches to problems. *

[oleg]

if i remember correctly the limmiter is in mike level posision only and it comes in -4.5 dbfs , it gang and effect bouth channels

[Barry_Green]

Hey Barry_S, between you and oleg, this audio forum is just chock-full of excellent info. You guys are required reading!

[Terry_Lasater]

I concur!

I believe that answering these questions is helping Oleg with his English as well.

Either that or I'm just starting to understand him better. ;D

Regardless, Oleg and Barry_S's advice is greatly appreciated.

[oleg]

sorry about my englis ,thats to many days on the beech durring the schooldays 20 years ago . now its to late and my memory isnt so good (you can see 5 differt way i can do spelling mistake in one word during 3 sentences) and i admit that iam to lazy export the letters to autlook and fix the spelling
sencirlly yours
Oleg Kaizerman ( gebe-Good Ears Bad English)

[Barry_Green]

Hey Oleg, do not worry about it one bit! Your information is very valuable, and your english is completely understandable. We all very much appreciate your taking the effort to write it in English in the first place, too!

[oleg]

i cant disconect my english limiter
its stucked in 6 gray ,ohh ...:-)
never been worry Barry

[Terry_Lasater]

Thank you, Oleg!

[ullanta]

if i remember correctly the limmiter is in mike level posision only and it comes in -4.5 dbfs , it gang and effect bouth channels


I'm not sure... I've been planning some experiments to gain certainty, but in my experience the ALC seems to be operating on line-level signals as well. I'll let you know when I find out. Oleg, where did you find this information? Is it empirical?

Also, unless someone has an answer, there was another forum discussing the nature of the "ganging." Anyone know if it's watching one channel, or the peak on both? I'll check that out as well...

-Barry

[Barry_Green]

Testing would be welcome. I also remember reading that it sets the limit at -4.5db, and that it starts its limiting process at -6, so everything gets compressed in just 1.5db of headroom.

And I'm fairly certain that the limiter is ganged to both channels. We were feeding -20db tone from a mixer and trying to get the DVX to match the mixer's output, and had a devil of a time because adjusting one pot would cause the other channel's level to rise... until we turned off ALC, then everything worked as you'd expect.

Those are quick observations though, not controlled testing.

[Guest]

Does the limiter work only with the internal mic or does it extend to the XLR inputs?

[Barry_S]

It works on both audio channels regardless of whether they're switched to the on-board mic or an external mic coming in theough an XLR input.

[scottchapin]

The last time I messed with this, I ran a test signal with my Neutrix Minirator through both channels. Oddly no matter how strong the signal, it would not break 4 red bars.

Obviously brief high level intrusions do in fact break the 4 bar level, but strong, steady signals do not. It's as though the compression ratio is variable and increases with signal strength to almost act as a brick wall limiter through which transient spikes get through.

[Barry_Green]

That's exactly how I understand it as well. If I remember correctly, the limiter starts at about -6db (3 dots down from max) and puts up a ceiling at -4.5db. Spikes may punch through, but overall loud noise gets clamped at -4.5.

[pete66]

Hi, I've been reviewing some live rock music footage of mine, in recording I simply put high end mics at 2 considered locations in the room and hooked them straight up to the DVX XLR lines.

The recording sounded good on playback (it was topping at 11 bars so there was no sign of red -but very close). Until I reached a part where I had accidentally bumped the audio level control up a few notches at which point it sounded absolutely unrivaled!

Of course this small section of aural brilliance only lasts about 10 seconds because when I was recording I realised immediately that the levels had started peaking out of control and required immediate "correction".

So I think the moral to my story is:
"if your levels aren't hitting red then your levels are too low"

and possibly

"if your levels are only just hitting red then your levels are too low"

Is having the ALC turned on a good idea for this type of recording?

Cheers
Pete

[dereksam]

I find that in a noisy situation (heavy traffic or loud music) that the indicator goes into red section very easily,
and I have to adjust the levels manually. then when in a more normal situation the levels are far too low; and I have to reset the controls, this is with a.l.c.on....I don`t completely understand. Can anyone help?

[oleg]

the alc is automatic limitter control , the limmiter activates in -6 dbfs and limit the audio to -4.5dbfs maximum to prevent you hit the digital brick wall 0dbfs( the last red befor nothing)
the alc doesnt do anything if the lsignal dont hit the -6 dbfs mark( the third red mark from the top) , so that have nothing with automatic gain control which exist on other cameras ( consumer or beta or big dv tipe) , so yes you must manually rise the level when it to low and decrise them not to activate rhe alc to much
each dot is 2db, for good recording try to stay between the 3rd and the 6 red on your picks , thats all right to be red - its better then to be dead ( sound)

[pete66]

OK so if I turn off the ALC and do a recording that just so happens to hit -1dbfs (what exactly does dbfs stand for?), is there going to be any more distortion than if it had been -4.5dbfs (limiter on)?

Why does it limit it to -4.5dbfs and not -0.5dbfs?

Thanks
Pete

[oleg]

If you not distort the analog stage of your camera preamp its ok , as long you hiy the -1 , the volium rise is in the digital domain , so be carfull - you might distort your sound and still be "ok" with your dvx levels
the dbfs is db full scale

here is the explanation in good english

http://www.jimprice.com/prosound/db.htm#dBFS

each device place the limmiter in different place , sony 150 put hard limiter in -1 dbfs , the panasonic probably becouse the slope and the activating time ,is much better , it much softer limiter of 1,5 db range and also come to prevent extrimly loud signal which can go ferder then -4.5bfs .
both channels are ganget with limitter so activating on one channel effect the secend as well

[MattC]

Pete, that can be dangerous advice sometimes... If you have a good clean signal you can always make it louder in post (L1 Maximizer from Waves is a great way to do this). However, once you clip you're done...

A limiter can be a good feature but it doesn't really prevent bad things from happening it just makes that bad thing sound less bad. A compressor (which is what I think Barry_S is referring to, can help prevent bad things. But, if I were going to rely on such tools, I would probably use outboard gear and turn off any level controls contained in the camera. Of course it you're doing that you might as well record to a better recorder...

Matt

[oleg]

if its not brick wall that not dangerous , dangerous if you dont know what are you doing , eventually if we are talking recording classical musik , i hit the -2 on tascam 98 allot of times ,dangerous - but you are going with smiling face to do the master , not for every one not for every situation .
so my answer was hipotetic about if it good , yes it is , if you have to do it , not nesserly:-)
about limmiter on dvx , usially the fast editing which go straight to the air asking and limiting the levels to _10dbfs maximum pick level to prevent problems with transmition , so the -6 is about in the eria that they wouldnt hire you again if it becoming to many , but for normal dialog for editting you have more s/n ratio and better quality signal ,
so the -6 dbfs is a nice place to put the limmiter , exacly where i like it ( i dont use it since have much better on the mixer)

[MattC]

You will note, Oleg, that I said "sometimes"... ;)

[oleg]

sometimes it dangerous indeed ::)

[pete66]

Please can I just ask, where exactly in the camera menu do you find the ALC option? I've had a good hunt through the camera and the manual and I'm really starting to think this could be a PAL/NTSC model difference -I have a PAL model.

Hopefully I'm wrong and someone can tell me where it is and I can say "Oh yeah, didn't see that".

[oleg]

camera setup menu near the 50 ,60 db input

[pete66]

Phew, found it. Thanks oleg, I think I was too tired to notice it listed as "MIC ALC" when I was looking for "ALC". Does the limiter affect XLR inputs?

cheers!
Pete

[pete66]

oops, that question was already answered earlier on in the thread, I told you I was tired!

[oleg]

the alc works in line mode as well