Anyone do an audio test on the AC-90 ??

C

ChrisHarding

Well-known member
Hi Guys

Has anyone yet discovered if the AC-90 uses the same audio boards as the AC-130??? My huge concern with the 130 was the ALC was totally useless! I'm mainly on manual for audio but at weddings where the ambient noise level/DJ music is constantly changing I use ALC....Now AFAIK all ALC features should limit the input level of the complete signal and NOT clip it!! The 130 keeps the signal high and basically clips the top half of the waveform (if you look at it in the NLE audio track) so the bottom half has it's normal peaks but the top half looks like it has been given an army haircut so the audio is flat and uninspiring.

It would be great if anyone could record some real loud audio with ALC on on the AC-90 and see if the signal from a mic is actually reduced (as it should be) or clipped like the AC-130 ??? My HMC's definately reduce the input signal and all the top half of the waveform looks perfectly normal so hopefully the 90 has audio circuitry that has gone back to that.

Chris
 
I'm actually quite surprised that nobody with an AC-90 has even examined the audio side of this camera? Decent audio is just as important as the image and it really would be nice to know if the ALC on the camera clips the signal like the AC-130 or not???

Chris
 
It's beyond comprehension why a limiter would just axe off the peaks - you would not want that for any music event.

I suspect best is to take an XLR feed from a sound board on CH1, then take an on-camera mic signal on CH2 where you set the sound dial a bit lower.

On top of that I bring a portable Tascam audio recorder. With three sound sources it's not too bad, a fourth would be even better.

I now bring a dual passive direct box plus a Whirlwind Impad20 barrel. I have not yet had the occasion/need to use these but I figure with all of this I am loaded for bear.

Not much point having your own mixer if you are a one trick pony, these things need an operator.

PluralEyes 3 apparently allows you to "easily" synch the sound from the recorder with what you have at the camera. I have not tried it.
 
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Hi Walter

At wedding receptions you are all handheld and moving during these type of events ... the ambient sound goes from loud to soft depending on the DJ and the song so using manual audio is really tough. I really couldn't see why a camera as classy as an AC-130 would require a digital recorder simply cos the ALC doesn't work correctly... Also you NEVER get feeds from DJ's at weddings ..they have no idea what to supply and also by getting a feed you are losing all the room ambience ... might as well just dub a copy of the song over the vision!!! All I really want to know is if Panasonic have used the audio circuitry from the HMC cameras for the 90 or the audio circuitry from the 130?? (The 160 again is different AFAIK) If the ALC doesn't work then it's pointless even looking at the camera from my point of view

Your suggestions however are much appreciated

Chris
 
2012-11 (Nov) 26 Audio test only of ALC on then Off on Panasonic AG-AC90 PJ. I varied the volume up and then down 1st clip. At the peak it was extremely loud and should have clipped easily. I detect some slight clipping in a couple spots on the 1st clip, but it was extremely loud. For how loud it was +90db off my 120 watt per channel amp I believe it did very well at 12" from the speakers with the internal microphones set to stereo. There is possibly a slight distortion in the speakers too, but they are very high quality towers. Don't listen to this off a cheap laptop speakers or they probably will clip on the first clip and misrepresent the test. The red peaks I am talking about are some very fine red lines on the LED. I kept the lens cap on for file size consideration. I didn't have much time to do this so youtube seemed to be the easiest option.
http://www.youtube.com/watch?v=gM5BmDlOAVQ

Tell me what you guys think.
 
Hi Steve

Very much appreciated!!! Yes , when you get a chance can you look at the waveform in your NLE and see if the signal has the weird AC-130 "haircut" effect of the top of the signal??

Many thanks again

Chris
 
Here's the waveform display from Steve's test. It looks exactly as I would expect. However, does the AC90 have a limiter, or just an ALC? I understand Chris' problem was only with the limiter.

ac90-audiotest.jpg
 
Chris, I didn't realise you had such a problem with the audio on the 130s beyond one post, and then you sold them so I didn't bother offering to get to the bottom of the problem, but I think it's unlikely that the 130 inherently has a problem clipping the tops of the waveform. However, I can think of situations that may make this happen. If you are interested in a little diagnosis after the event, can you post an example of the waveform, or better yet, email me a short segment (a couple of seconds as an MP3).
 
Mike Warren said:
Here's the waveform display from Steve's test. It looks exactly as I would expect. However, does the AC90 have a limiter, or just an ALC? I understand Chris' problem was only with the limiter.

ac90-audiotest.jpg
Click to expand...
I love seeing that waveform. I sure am curious how you got it. If I knew how I would have published it. So if I understand it, the "haircut" on the right side isn't the same problem with the AC-130 its just clipping & distorting. I don't see any other limiter settings in the menu. The manual only mentions ALC and doesn't even say what it is. Maybe it stands for Automatic Limiting Control. Like I said when I recorded the first clip is way way louder than the 2nd and 3rd parts. Like a very loud house party loud or maybe even louder. The first clip with ALC on in this waveform sure doesn't show any clipping/haircutting to me.
 
steve4505 said:
I love seeing that waveform. I sure am curious how you got it.
Click to expand...

1/ I downloaded your video from YouTube
2/ Imported it into Premiere
3/ Expanded the waveform view
4/ Pressed the print screen key
5/ Pasted into Photoshop
6/ Cropped
7/ Saved
8/ Uploaded


So if I understand it, the "haircut" on the right side isn't the same problem with the AC-130 its just clipping & distorting.
Click to expand...

I may also be misunderstanding what Chris was seeing, but I assume it was just clipping on the top side, something like this (simulated):

audiohaircut.jpg


The manual only mentions ALC and doesn't even say what it is. Maybe it stands for Automatic Limiting Control.
Click to expand...

ALC stands for Automatic Level Control. What it does is adjust the audio level automatically.

Conversely, a limiter requires you set the level manually, but it will turn down the level automatically when it gets too loud. A limiter requires a bit of thought to operate, but when used properly will give a better result than an ALC.
 
Mike Warren said:
ALC stands for Automatic Level Control. What it does is adjust the audio level automatically.

Conversely, a limiter requires you set the level manually, but it will turn down the level automatically when it gets too loud. A limiter requires a bit of thought to operate, but when used properly will give a better result than an ALC.
Click to expand...

Oh I could have done that. I never thought of screen capture.

Sounds like an old debate that I've never paid attention to (till now). http://www.dvinfo.net/forum/all-things-audio/31466-limiting-vs-compression-vs-agc.html and http://www.dvxuser.com/V6/archive/index.php/t-277645.html What I see is missing on the AC-90 is its not channel specific. The 2nd link is saying on the AF 100 its a Automatic Limiter Control. Page 49 of the manual just uses the same acronym, so I would assume its the same and they are calling it a limiter. My tests I think prove its the "better" limiter because otherwise it would have raised my voice to much higher levels than it was.
 
Hi Guys

Many thanks ..all looks good there WHEW!! Mike? I had the limters on when I used the 130's and yes almost like your example but more drastic and quite correct it only shaved the top of the waveform...I didn't sell the 130 because of audio!!! It was simply the fact that the camera autoiris range was way too tiny to allow the camera to run solo ..one cloud over the sun and it needed an ND change!!! I just wanted to find out if the limters worked the same....The old Panny GS400 had the same sort of system called Manual + ACG It allowed to to have manual but limited signal level to +8db ... I'll dig out the clips from last March and post them here!!

Chris
 
ChrisHarding said:
I had the limters on when I used the 130's and yes almost like your example but more drastic and quite correct it only shaved the top of the waveform...
Click to expand...

That makes me strongly suspect there was something odd going on. The only way a signal can be clipped non-symmetrically is if there is a DC bias to the signal somewhere in the chain. It would be such a stupid beginner design mistake to make that I think the chances of the bias being inside the camera would be close to zero.

Either, there was a fault in one of the cameras (but I'm sure you would have tested both) or, more likely, there was a DC bias being introduced elsewhere. Theoretically, the inputs to the camera should be capacitively coupled. However, this is sometimes not the case for balanced inputs in relation to each other. Your mic may be putting out a DC bias which is being removed by the input circuitry of your 82s, but perhaps the 130/160 don't have input capacitors.

There is a good reason not to have input capacitors. Series capacitors roll off the bass frequencies and it may be that they were omitted on the more expensive cameras to improve the audio spec.

As usual with my posts, this is all speculation, not having access to schematics.

I didn't sell the 130 because of audio!!!
Click to expand...

Sorry, I understood that. What I meant was that I didn't put any effort in to explaining possible causes because you had only made one post (that I saw) about the audio before you sold the cameras.
 
Hi Mike

I actually didn't test the "A" Cam as I only use it for some prep shots and ceremonies/speeches .It was the "B" cam that had to contend with loud DJ music at receptions via a Rode Videomic ...normal audio worked perfectly on both cameras it was just the issue with really loud music!! Funny too that I found the 130's to be totally inaccurate regarding mic input ..I had to push the input level to -60db to get decent audio yet on the 82's I only need -50db in the same situation.

I will grab myself an AC-90 anyway as I need it for Realty shoots..my old arms struggle with the 82 now. I really liked the form factor of Sony's new EA50 but the fact it has a still camera sensor put me off ....rather just make a little ENG rig for the 90!!

All your effort is greatly appreciate plus of course Steve going to all the trouble doing a test for me!! Thanks again guys!!

Chris
 
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