CLipping

B

bwest

Well-known member
Funny thing happened the other day, I did a sit-down interview for a friend and I recorded with the dvx100a camera direct to laptop…. no tape in cam. My capture program was DVRack. I used an AKG ck63 from the tabletop, just out of frame, approx 2.5 feet from the interviewee. I powered the mic via dvx and fire wired to laptop. I used my 7506’s and watched my camera levels [red dots] to monitor sound. I heard some clipping so I turned the cam levels down to 10:30 [L] and 10:00 [R] at both channels, which seemed to clear things up to my ears and eyes?

At the end of the session I replayed DVRack and to my surprise, I had extensive clipping. So I transferred the recording to my NLE and replayed it there and I hear no clipping? And my meters in the NLE are going from –12db to –1db?
I did a quick DVD burn and I hear no clipping on the TV speakers?

I’m thinking hard as to what I did wrong, so I came up with a list of possible “no no’s ”
First of all if my NLE shows no clipping, am I clipping? [I think maybe yes]
1. The tabletop mic was pointed directly at the speakers face.
2. I didn’t use the in camera pad, any attenuation, or my mixer with its limiters.
3. I didn’t monitor from the laptop…headphones where in the camera with no tape?

Funny thing it seems to me is: If I had monitored from the laptop I probably would have heard the clipping and would probably have turned my camera levels down to 9:00…the lowest you can go? That seems low?
I intend to play around with this some more to see what I can learn…but I thought I would post this first.
 
Are you sure DV Rack indicated audio clipping?

The Quality Monitor in DV Rack uses red marks to signal possible audio problems, with marks at the top and bottom of the display to indicate clipping, and marks halfway between the center line and top/bottom to indicate popping.

My guess is you had popping indicators, given that the mike was close to the subject.
 
Well, dumb me I didnt watch the Audio monitor in DVRack...which I use to monitor my video quality more than anything else. I did see some yellow bars and only the occasional red bar...but I hear that crackling on the hard vowels. I dont think thats pop, but a pop filter maybe belongs on that list.
 
Yellow is for video problems, not audio.

It indicates that you exceeded the selected exposure level. It's somewhat like zebras, but you can set not only the IRE level, but also the area and duration.
 
ahh that maybe, Ill take another look, but I do record hot with the video, and bring down in post...not too much, but I open the apeture up and watch the zebras. I have no complaints videowise, it seems to be what I expected...great for a little post....my intent. When monitoring audio I tend to trust my ears, but maybe I'm on the verge of learning something! Like: can a dumb newbie record clipping and not know it?
 
I would suggest having another look at the documentation or the help file. If you intend to use DV Rack as the basis of making adjustments to your recording setup, then you need to understand what the program is telling you, or you could wind up with disastrous results.
 
There are a lot of places where clipping can occur. One thing is many meters show "clip" before you have actually clipped, not much before but a bit. So it is poss to have clip indicators with out actual clipping. These are general notes by the way I've never used the software your talking about so YMMV. Second your talking about "hearing" clipping. So other parts of the chain come in like the headphone amp. It is quite poss that the headphone amp on the laptop was clipping even if the signal isn't clipping. THe DA-P1 for instance had a very under powered headphone amp that would clip way before the signal being recorder was clipped. It's poss that the software was sending a stronger signal than expected. This is a Windows machine I believe (I don't think DVRack runs on Mac's) and I remember issues with levels back on my Windows box (admittedly a while ago), this may not be an issue now but was in the past. Can happen on the Mac also but the whole chain is under tighter control (restrictions) under Mac OS so it's a bit less likely. If the NLE is not on the laptop then I suspect the headphone amp on the laptop was clipping and not your signal. A whole other can of worms is metering and what it shows. Most metering on computers reads the highest level as the peak. The problem is that because it's looking at samples it's not reading the peak that happens between samples. So if you have a fast transient that is going to spike at 0 the peak reading can be as low as -3 on most meters. If they are very short you may not even hear it as a clip but as a slightly edgier sound. The point is recordings that peak at -1 are to high for any kind of safety. I would aim at peaks no higher than -3 but probably a little more conservative at -6 or so.
Be more careful with the chain and monitoring and be happy it worked out the right way this time.
 
hmmmmmmm...my reds on the dvx were at around -6db so I thought I was conservative? The right channel was set even lower for back-up! This laptop is of 2005 vintage, a big p-4. And my NLE [vegas-7] is on the laptop as well? Im wondering if I should have monitored from the camera's rca outs instead of the headphone outs? Something about before and after the adc? Though using DVRack is a luxory to have...esp for the newbie, I cant bring it everytime I do a shoot!

Noise2, Is it possible to be clipping, though I dont see it or hear it on NLE... or my burn dvd? I know your a big post guy. Im afraid other tv's, other than mine, will pick up that God awful crackling sound. Im going to have a distribution on this...like a whopping 20 dvd's in total. lol
 
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Its very possible its the amp on the laptop that was clipping my laptop speakers. I dont see that chopped [tops] waveform in the NLE, and my DVD burns sound good. When one wears headphones to listen during a performance, where does the clipping begin...in the ADC or in the headphones? If Im recording to laptop with the camera [via firewire; no tape] in-which the ADC is in the camera, isnt it better I monitor with the headphones from the camera vs the laptop? Or does one always monitor from the recorder?
 
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