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AGC and limiter for audio

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jim stamos
AGC and limiter for audio
on Mar 11, 2012 at 9:49:43 am

i shoot alot of events and noticed tonight that some of my audio seemed too hot. should i have my AGC set to High or Low and what does the limiter do? i have to On.
will having it set to High cause what happened?input welcome


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Don Greening
Re: AGC and limiter for audio
on Mar 11, 2012 at 11:34:10 pm

You haven't provided much information about what you're recording and if you're using line level input (from a house mixing board) or mic level from a radio transmitter or a hard wired mic. I think you might be talking about mic level but I'll touch on line level just in case.

If it's from a mixing board here's some recommendations. First of all, a professional mixing board's peak signal is +10dBu whereas your EX peaks at -12dBu. Most audio people round off the -12dBu peak signal from a video camera to -10dBu and refer to this as the "ten+ten" rule. As you can see, there's a huge difference in signal strength between the two. Setting your camera's inputs to line level will solve the mismatch in most cases but in others it's simply not enough to knock the board's signal down for the camera to deal with. If the signal coming from the board is distorting, no amount of camera gain lowering will fix it because the signal is too much for the camera's pre amp. The solution for this is to purchase one or two inline adjustable attenuators like the ones at the link below:

http://www.audio-technica.com/cms/electronics/a05620466ab0ce16/index.html

These plug in to the XLR cables the mixing console has sent to you then in turn plug into yours before the camera. You can adjust them to minus 30dBu in 10dBu increments.

If you're requesting advice about mic level signals then I invite you to read the recommendations at this link:

http://forums.creativecow.net/readpost/142/878123

- Don

Don Greening
A Vancouver Video Production Company
Reeltime Videoworks
http://www.reeltimevideoworks.com


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jim stamos
Re: AGC and limiter for audio
on Mar 12, 2012 at 3:41:01 am

don, i was shooting a wedding reception as i have many times before.
i had my agc on high and my limiter on . is there any audio software that can improve this audio? all my dance footage at the reception sounds hot.has to be something to improve it to a level that bride wont notice


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jim stamos
Re: AGC and limiter for audio
on Mar 12, 2012 at 3:41:59 am

maybe i should keep the audio on agc low from now or go with a small shotgun. someone suggested the rode nt5.


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Don Greening
Re: AGC and limiter for audio
on Mar 12, 2012 at 4:57:46 am

Whatever mic you were using to record the loud music was too sensitive (too hot) for the job. The signal was over-driving the camera's pre-amp and that's why you got the distortion. You can try trimming the signal in the menu but I suspect you'll still get distortion even at a quiet volume and with AGC active. To solve the issue you need to get a mic that's much less sensitive. Since I don't record loud music I can't advise you on what to buy. for example, a good shotgun for recording the spoken word is not going to do a good job of recording loud music.

You also can't fix digital audio in post once it's distorted. Digital audio turns into hash as soon as distortion happens, whereas analogue audio is more forgiving and can be manipulated somewhat.

- Don

Don Greening
A Vancouver Video Production Company
Reeltime Videoworks
http://www.reeltimevideoworks.com


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Bob Mark
Re: AGC and limiter for audio
on Mar 12, 2012 at 3:41:37 pm

All very true. That's why you need to monitor the camera audio with very good set of headphones that will let you know if the audio is too hot. Relying on the meters alone is suicide.

Bob


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Dean Longfield
Re: AGC and limiter for audio
on Mar 12, 2012 at 4:30:40 pm

Hi,

I have an EX1R and have been slowly testing it in the field. On events with loud music I have found the same problem that Jim had. I tried using both the built in mic as well as two shotguns. All I did to adjust the audio was to put the Audi-In setting on Manual and adjust the levels. That does not cut it on the EX1R. Others here on the Cow have suggested that I lower the Trim Level, which is what I'll try next. (Ext Mic Input, Manual Audio, and bring the trim down). I'm thinking of bringing it down to the -32 or so range and adjust from there. I'm also going to try switching the high/low setting on the AGC, but am hoping that the low is not too muffled. I'm not sure about the gain setting but I initially am planning on leaving it on '0' and taking it from there. This time I'm bringing an attenuator as well,
just in case all in camera methods are not providing suitable results.

Re: Mics: I made the mistake of using a Sennheiser ME-66 indoors with very amplified (LOUD) sound. Not a good combo. Then I used the mic from the old DSR cameras (300/500 series) and that wasn't really much better.

So I'm going to purchase the Sony recommended mic: the Sony ECM-673/9x Shotgun mic.
It's an Electret Condensor and has a Super cardiod pick up pattern, (just like the DSR mics).
AND am going to experiment with setting the levels as described above.

There has to be a workable combo of mic choice and audio settings. It's just a matter of finding it.
With the EX1R, I've been recording sets that are not critical to the edit, so if they don't come out well I
don't use them, (I use other cameras, that I'm used to, for the critical footage).

When I find the right combo, (that works for me), I'll report back.

Good luck.


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Bob Mark
Re: AGC and limiter for audio
on Mar 12, 2012 at 5:05:35 pm

The problem you are experiencing comes from using microphones that do not have a high enough SPL (sound pressure level) rating. Many shotgun microphones have this problem. The ME66 is well know for this overload issue. The Sony shotgun you mentioned does not have a better SPL rating than the ME66. They are both around 125 db SPL. Some mics like the Shure SM81 (not a shotgun) have a built in pad that will take the SPL up to 146 db. AKG makes some nice mics for music recording as well. Shotguns are designed to reach for sound, so that comes into play too. Is there any place you can rent some mics to test? Good luck.

Bob


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jim stamos
Re: AGC and limiter for audio
on Mar 13, 2012 at 6:21:32 am

i never had a problem with this issue with my dsr300 and i shot 100s of receptions.
is the recommended mic for the ex1r going to be as bad as the oncam mic? would hate to throw money and time away if it wont do the trick


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Brent Dunn
Re: AGC and limiter for audio
on Mar 12, 2012 at 7:04:32 pm

The limiter will limit the amount of audio, keeping some of the peaking levels to a set level. Compressor's can also squeeze the audio.

For receptions, I use the automatic gain, since the audio is all over the place and I don't have any silent spaces where my gain will boost. It's worked very well for me and I don't have to worry about distortion. I use a wireless either plugged into the board or a handheld mic on a stand in front of the speaker, as well as an on camera mic for the 2nd track of audio. For better audio, you may want to invest in a Zoom H4N recorder.

Brent Dunn
Owner / Director / Editor
DunnRight Films
DunnRight Video.com
Video Marketing Toolbox.net

Sony EX-1,
Canon 5D Mark II
Canon 7D
Mac Pro Tower, Quad Core,
with Final Cut Studio

HP i7 Quad laptop
Adobe CS-5 Production Suite





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Bob Mark
Re: AGC and limiter for audio
on Mar 13, 2012 at 5:12:10 pm

It all comes down to how well the microphone handles loud sound levels (SPL). If the mic is clipping you are a dead duck. No amount of mixer or camera audio adjustment will save you.

Bob


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Dean Longfield
Re: AGC and limiter for audio
on Mar 13, 2012 at 5:58:38 pm

I agree Jim, I never had a problem with the stock mic on either a DSR 300 or 500 series camera, That's why i tried that same mic on the EX1R - figuring it would work good on the EX1R also. It did not work well at the default settings (-41 trim..etc.).

As has been correctly pointed on this thread by others, the SPL on the stock DSR 300/500 mic (125-SPL) has the same 125-SPL as the recommended shotgun, (Sony ECM-673/9x), . for the EX1R. So after giving it more thought I decided to try the Rode NTG-1 rated at 139-SPL, which is also a Condensor mic with Supercardiod Pattern, but with the higher SPL.

So I'll run my tests with that as the on cam shotgun mic, and see what happens.

Yes I also put a mic by the speaker and point it off axis, not directly into the speaker.....
Right now I'm just running tests with the on board built in mic and an on board shotgun, at non-critical times, on loud music type jobs.

Will let you know how the tests go.


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Bob Mark
Re: AGC and limiter for audio
on Mar 13, 2012 at 7:04:52 pm

Start to raise your trim pad on the EX1(r) until the signal sounds clean and you have a volume control level around 4-5.

Bob


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Don Greening
Re: AGC and limiter for audio
on Mar 13, 2012 at 8:22:38 pm

The moral of this story is that you can fix low audio volume in post but you can't fix digital clipping in post. It's sort of like a computer speed test: lower bars are better.

- Don

Don Greening
A Vancouver Video Production Company
Reeltime Videoworks
http://www.reeltimevideoworks.com


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Bob Mark
Re: AGC and limiter for audio
on Mar 13, 2012 at 10:04:53 pm

That's right. Remember when we made the hop from analog to digital and the audio on bars and tone on analog equipment at 0 VU became -20 or -12 db on digital gear? Analog can handle a certain amount of overload and not sound too bad, in fact recording studio engineers used to hit the analog tape recorders with a hot signal(+6 or more) to produce the fat sound of tape compression. No can do with digital.

Bob


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Brent Dunn
Re: AGC and limiter for audio
on Mar 15, 2012 at 2:19:25 pm

crap in, crap out

Brent Dunn
Owner / Director / Editor
DunnRight Films
DunnRight Video.com
Video Marketing Toolbox.net

Sony EX-1,
Canon 5D Mark II
Canon 7D
Mac Pro Tower, Quad Core,
with Final Cut Studio

HP i7 Quad laptop
Adobe CS-5 Production Suite





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Dean Longfield
Re: AGC and limiter for audio
on Mar 19, 2012 at 7:18:24 pm

Hi,

i tested the EX1R again, in a loud music from a DJ type scenario. I used the Rode NTG-1 on Channel 1 with the trim set to -32 and the (exterior knob on camera) manual audio level set to about 3-1/2 to 4. These settings seemed to work very well. (The Channel 1 music was recorded at an audio meter level of about -20).

Channel 2 was the internal mic. The INT MIC LEVEL setting in the menu was left at the
default setting of, '0'. the (external knob on the camera) Manual Audio level for Channel 2 was set at around 2- 1/2. Channel 2 was recording louder than Channel 1 but never peaked in the red. Now monitoring audio on a very loud dance floor is not easy but the sound appeared to be OK on this channel in the headphones. However upon bringing it back and loading it into the editing system, (the audio is recorded at an audio meter level of -12), and never peaks in the red but it sounds almost distorted. Not crisp and at times has some distorted crackling sound as if it is peaking in the red.

Re: Internal Cam Mic Levels:
Should I set the INT MIC LEVEL lower at say -6 ?

Also it appears the MIC AGC level is for both channels, (you can't have one on high and the other on low). Has anyone tried the LOW setting and if so does that significantly alter the sound quality, (eg, muffled audio) ?

Thanks.


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jim stamos
Re: AGC and limiter for audio
on Mar 19, 2012 at 10:23:11 pm

so are you saying i will be safe going with the rode ntg-1? i shoot a ton of receptions, but just started with my ex. never had an issue with the mic on my dsr300 for years.
you would think sony would have a recommended one for the ex1r that will give me good audio


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Dean Longfield
Re: AGC and limiter for audio
on Mar 22, 2012 at 6:30:37 pm

Re: Jim's question if we're safe using the RODE NTG-1 in loud music environments:

I don't know if we're "safe" with the RODE NTG-1, but I do know that it worked well on the last shoot I did, which had a semi-loud DJ providing audio services / music in a nightclub. It appears that the
NTG-1, (with a maximum SPL rating of 139), coupled with adjusting the Trim Settings in the menu, and adjusting the Manual Audio Levels on the exterior of the camera itself, enables one to attain a desirable audio record level.

( BTW: The INTERNAL- built in - mic is something I have to test more in loud music environments before I find an acceptable setting.)

The recommended Sony shotgun Mic for the EX1R is the SONY ECM-673/9X which apparently works nicely with the camera, BUT only has a max SPL rating of 125, so being that I, like you, am often in loud music environments when recording, I opted to go for the RODE NTG-1, (with a max SPL of 139),
being it gives one that added padding - ( as others on the Creative Cow have so generously pointed out, and THANKS for doing so as that was very useful info ! )

My initial impression of the RODE NTG-1 as the shotgun mic on the EX!R:
so far so good, but I've only tested it once.


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jim stamos
Re: AGC and limiter for audio
on Mar 22, 2012 at 7:12:33 pm

is the rode much longer than the sony? how did you secure it in the mic slot?


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Dean Longfield
Re: AGC and limiter for audio
on Mar 23, 2012 at 6:11:55 pm

The Rode is 1"longer. I secured it in the mic slot by wrapping thin foam
around the mic where it's in the mic holder.

I've heard that many people replace the mic holder with third party brands. You can find such attachments by searching the net.


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jim stamos
Re: AGC and limiter for audio
on Mar 23, 2012 at 6:22:06 pm

i saw those adaptors, they would work better. is there a mount to put that mic on a shoe?


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Dean Longfield
Re: AGC and limiter for audio
on Mar 23, 2012 at 7:16:07 pm

There are shoe mount adapters with shock mounts that fit the NTG series of mics.
I don't know if there are other type of mic holders with shoe mounts that fit it. Haven't got that far yet....


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