strange audio on DVX100

J

jbeale

Active member
I just tested my DVX100 line-level audio input using the "Rightmark" audio benchmark software and a good soundcard as a source (Echo Audio "MIA"). I tested two other video cameras and two MD recorders with the same setup- all worked about as expected. But the frequency response of my DVX100 is unexpected, to say the least. Has anyone else tried this test? What's your opinion, is mine just broken? What could even cause this?

http://beale.best.vwh.net/measure/audio/DVX100.htm

(look at the first graph, labelled "Frequency Response"

I have an original AG-DVX100P, not the newer "A" version, and my S/N is 12TD00467 if that's relevant.
 
Re: strange audio on DVX100

I've got to think that you're experiencing some testing artifacts rather than measuring the actual frequency response of the DVX100.  If the curve were that bad, the sound quality of the DVX would be terrible--and it clearly isn't.  Record a frequency sweep with your DVX and listen to the results. I'd be pretty surprised if you heard all the dropouts on that curve.
 
Re: strange audio on DVX100

Ok, I just noticed that you're feeding the DVX a + 4 dBu line level signal.  +4 dBu is a professional standard line voltage.  I believe the appropriate line level for the DVX100 is -10 dBV.  The anomolies in the frquency curve may be due to overloading the input.  I know it says ALC off, but the limiter kicking in intermittently might produce something as funky as that curve.  Are sure it was off?  Your input isn't set to mic level--right?
 
Re: strange audio on DVX100

+4 dBu is pro, but then the DVX is advertised as pro... I'll try again with a lower level. The limiter is off, at least the menu says so. In fact I first tested it with the limiter on, and its action was quite visible as the amplitudes got turned down. Yes, both inputs are switched to line level.

I tested all my other gear the exact same way, and my other cameras and MD recorders were very flat in frequency (with expected high and low-end rolloffs in some cases).

Just now, I generated a 20-second log frequency sweep from 40 Hz to 15 kHz using Cool Edit 2000. On playback from the DVX100 you can hear pronouced dips in amplitude, and the recorded data from firewire shows this, agreeing with the original test. Here's a screenshot of the envelope as it came back from the DVX (the original source was ruler-flat).

+4: http://beale.best.vwh.net/measure/audio/DVX-40-15k-sweep.png

-10: http://beale.best.vwh.net/measure/audio/DVX-40-15k-sweep-10dBV.png

First image was at +4 dBu input, second at -10 dBV input. In both cases the audio input level pots are straight up, 12 o'clock position. I could see the dips on the DVX's audio bar graph display while the sweep was being recorded. Again, none of my other recording gear does anything remotely like this. I just tested an Akai DPS-16 hard-disk-drive based recorder with the same source, it is very flat.

I'm pretty sure my camera is broken in some strange way, but if anyone else has tried this on their DVX I'd be very interested to see your results.

As far as the audio quality I hear with normal program material, I've used it for some wedding interviews and organ music and it's not "obviously" bad but I could say that it does have a sort of "harshness" too it. Hard to define exactly.
 
Re: strange audio on DVX100

Something very funky is going on here. I'm in the middle of rebuilding my computers, but I will try recording a sweep when I get a chance.
 
Re: strange audio on DVX100

This is John Beale, right? Didn't you report something similar quite a while ago, during your first audio test? I seem to remember that Adam Wilt tested it and said that he wasn't able to duplicate that effect, so I think you're probably (unfortunately) right, that there's something broken with that particular camera. The DVX audio performance has been superb for most of us, and Jay Rose gave it a clean bill of health, so I'd strongly recommend you try to get a second camera to put through the same tests for a baseline reference point...
 
Re: strange audio on DVX100

Yeah, that's me, and it's looking like I'm just unlucky. I did hear that Adam Wilt and Jay Rose had no problems with it but I'd be curious to see a graph of this particular thing (frequency response) measured in a comparable way.

OK- Does anyone in the vicinity of Mountain View, CA have a DVX100 they might loan me for half an hour or so? I could reward you with your very own individualized frequency response chart....
 
Re: strange audio on DVX100

Yeah, I think you need to send your camera in to Panasonic for service. It looks like a major problem with your camera if you're hearing big drops with a sweep.
 
Re: strange audio on DVX100

Welcome to the forum!  For those who don't know about John's site (bealecorner.com), it's required reading... lots of great articles, comparison tests, resolution charts, just a boatload of great info.

We have something like 2500+ members now, so hopefully one of our members will stop by and help you get to the bottom of the issue.  C'mon someone in California, help Mr. Beale out! :)
 
Re: strange audio on DVX100

Historical note: Adam Wilt and Jay Rose (who really are experts with cameras and audio) reviewed the DVX100 in DV Magazine in December 2002: http://www.dv.com/reviews/reviews_item.jhtml?category=Cameras&LookupId=/xml/review/wilt0203

This is what they reported about the audio:

"Frequency response was remarkably smooth: 25 Hz to 18 kHz ± 2 dB, with a couple of insignificant, narrow dips at 130 Hz and 280 Hz. Distortion (THD+N) was 0.14 percent for line-level inputs, rising to 0.18 percent for a -50 dBu mic. With a +14 dBu input - well into the headroom of any professional mixer - distortion was only 0.3 percent. Signal-to-noise ratio, relative to a 1 kHz signal at -12 dBFS, was -60 dB for line and -58 dB for mic inputs."

They did not publish a graph of frequency response. My number for THD+N (0.13%) is essentially the same as they measured. (I would call this "OK" but not "Great" -for example, using the same test gear, I measured my Akai DPS-16 at 0.002% THD+N, and a lowly Sharp MD recorder at 0.003%.)

Jan Crittenden, Panasonic product manager, responded to me (on a Sunday!) and it looks like I'll be sending my camera in for service.
 
Re: strange audio on DVX100

To follow up on this issue: I sent my camera to a local Panasonic-authorized service shop along with my measured graph of frequency response. After three weeks and a $110 service fee I have the camera back with the receipt:

THIS UNIT WAS EXTENSIVELY TESTED FOR SEVERAL DAYS
NO DEFECT OR IMPROPER OPERATION WAS FOUND.

The service guy said Panasonic specifies only 20-20kHz response, but they don't specify +/- xx dB. (mine is -10, +2 dB.) He also said, it's a prosumer camcorder, it's not the last word in audio recording.

The service shop only had an oscilloscope, not even a sweep generator let alone spectrum analyser so they did not measure the audio quality besides a subjective listen test using spoken voice. They thought my frequency plot was a "very sophisticated test".

Bottom line, apparently my camera is not broken, but my minidisc (MD) recorders have equal or better audio performance than my DVX in every subjective and objective test. FWIW.
 
Re: strange audio on DVX100

That doesn't sound satisfactory at all. I would strongly recommend, if possible, getting another DVX and running it through the same tests. I still think that what you're experiencing is an anomaly and shouldn't be representative of all DVX's...
 
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