AUDIO GLITCHES!!! Octava? HVX? Cable?

[shortnstout]

Hi everyone,
Didn't know whether to post this in the Audio section, but I'm using an HVX sooo...

http://www.shortnstout.net/Audio%20glitches_1-2.mp3

Please listen to this sample of some audio problems I've had. Its the first event I recorded using the Octava and also the the first with the HVX. I spliced together about 3 glitches that are easy to hear and sound pretty similar to one another. It didn't occur that often (maybe 5 times in 5 hours of shooting), but none of these sounds are acceptable.

-Octava Black MK-012 in BBG mounted on camera
-1ft XLR w/ Neutrik connectors from the Sound Room guy (who sells the Octavas)
-HVX recording to miniDV

I believe I had this happen in more than one location that day. I'm pretty sure I didn't hit the cable or anything.

Any idea what this is, where it's coming from, or what to do first to fix the problem?


Please help!
Thanks!!
SNS

[mainstreetprod]

Sounds like cable or connection problem to me. I've heard that sound many a time when fooling with RCA connections and losing good ground, or touching/affecting the ground. I would try another cable. Another possibility is an internal mic problem (loose wire to capsule). Have you been using an external mic previously and never had a problem?

[shortnstout]

Thanks for the reply. I haven't been using another mic. The camera and mic and cable are brand new and this was my first event using them. I'll try another cable first I guess.

[Ted Spencer]

Ok, professional audio engineer here, to the rescue!

Those glitches sound to me almost certainly to be digital dropouts, and not anything to do with the analog side (mic, cable, etc.). What I heard at least twice in the clip was a sort of "bzzzzzt" sound for about a half-second, following (and followed by) a clean section. In my professional opinion, that specific sonic artifact is the sound of a digital audio converter "filling in the blanks" when its effort to produce clean digital information is compromised. What it does in these cases is to take a chunk of the clean audio just before the dropout and repeat it as many times as necessary to fill in the gap. In this case the audio "chunk" would appear to be about a 20th of a second's worth, which is why when it's looped it produces that brief "motorboating" effect.

Its visual equivalent in a faulty digital video transmission is a brief freeze of the existing image. It's the same idea: fill the corrupted "hole" with the previous moment's clean material, derived from an error-correction buffer that's designed to deal with just these situations. It's arguably better than black in the case of video, but in audio the advantage is not so clear, since the looped chunk really has no coherent content. Audio is *absolutely* temporal, and thus, unlike video, can't be successfully "frozen". Nonetheless, that's the process, and I'm 99% certain it's what you're hearing there.

As to the cause of the problem, my first guess would be tape dropouts, but I think you would probably have a video glitch at the same time if it were. It's still possible though I suppose, even if not. Next I'd suspect the digital to analog (D/A) or analog to digital (A/D) audio conversion circuitry in the camera. A failure there in either case would very likely cause that kind of audible effect. If the problem doesn't go away when diffrerent tapes are used, or in particular if it happens with P2 cards or direct firewire-to-computer recording, I'd take the camera in for service.

I hope this helps!

[The Engineer]

These are tape dropouts. Leave the mic and cable alone, they are fine. Check if it's something happening on the video at the same time (not necessary, but possible).

[shortnstout]

thanks for the replies! Nothing seems wrong with the video, just audio. Would it have anything to do with some setting? I think we were using bad tapes- they were the 60min Maxell ones from B&H that are pretty cheap. I've just ordered some panasonic tapes, and I hope that cures the issue.

[Lenilenapi]

If you are changing tapes or especially using cheap tapes it could easily create audio only dropouts. NEVER USE CHEAP TAPE. I would suggest sticking with one brand, but people disagree about that. art anyb rate you may need to clean your audiop heads now if you're getting dropouts.

[The Engineer]

No setting will make your camera perform with cheap crap. Remember the GIGO phenomenon and spend few dollars more (not many) on proper tape. Maxell is notoriously bad, I wouldn't get my 9 yo to use it for his home videos. Give the camera a tremendously good clean befor you start using proper stuff - the AMQ is my first choice.

[The Engineer]

Lenilenapi, there's NO "audio" (dedicated) heads in DV format... Everything is done by the video heads, the actual audio is blocks of info written at the beginning of each segment of video.

[shortnstout]

So then how would I go about cleaning whatever would need to be cleaned because I used these tapes. I used about 5 Maxell tapes in the camera so far.
Also, will the Panasonic tapes be okay? I would think they should be.
thanks!

[shortnstout]

We had ordered 2 kinds of Panasonic tapes recently:

http://www.bhphotovideo.com/bnh/controller/home?O=4121&A=details&Q=&sku=177607&is=REG&addedTroughType=categoryNavigation

http://www.bhphotovideo.com/bnh/controller/home?O=12650&A=details&Q=&sku=240000&is=REG&addedTroughType=categoryNavigation

I guess the 2nd link is the one to go with and I should never use the top link?
And by cleaning the heads, did you mean that I could just run one of those head cleaning tapes that I've used in decks or is there something more professional I should do for the camera?

[dusterdoo]

How did you capture the footage ? PC or MAC ?

AHHH - you were using 90 minute tape ? Possibly the culprit. .

I use Panasonic AY-DVM63MQ, available at EVS and B&H and elsewhere. . .

.

[THoff]

I guess the 2nd link is the one to go with and I should never use the top link?Actually, no. On page 31 of the manual for the camera, Panasonic states NOT to use 80 minute tape. The 80 minute tape media is physically thinner to fit more of it into the cassette, and the tape mechanism in the camera isn't designed for it.