OT: Audio cracks when played in theatre

kunal wrote on 4/24/2007, 10:37 AM
I know this is OT, but I'm only 15 days away from premiering my feature and I'm running into this issue and was wondering if anyone can give any pointers.

I recently did a test-screening of a 25 min segment of my movie (projected it from a mini-DV tape) in the theater in which we will eventually be premiering. The problem that worried me the most was the audio - whenever there was any dialogue/voiceover, the audio would "crack" - almost like the high frequency components were being amplified too much? I didn't see this problem with SFX or ambience - only with dialogue/voiceover.

When I play the tape on my TV, it's perfectly okay (even with the volume turned up all the way). Also, when played in my sound designer's professional studio, this problem doesn't appear.

Any ideas as to why this could be happening? I highly doubt that there could be a problem with the theater's sound system (as they're a pretty big theater in town - but then again, you never know...)

Thanks much for any help!
K.

Comments

John_Cline wrote on 4/24/2007, 11:11 AM
Something in the playback chain is clipping. Clipping is the term used to describe where the output voltage range of an audio device simply runs out of headroom and can go no further. Gross clipping manifests itself as the crack you describe. It's not your source, so it much be in the theater's audio system. There are any number of places in the audio chain where this can happen. If one stage clips, then the effects of the clipping will be in everything from that stage forward. I suspect the preamp or mixer into which you have plugged your DV camcorder is somehow overloading. It's all about how you have their gain structure set up in the chain. Perhaps they are running your audio into a mixer of some sort, like a Mackie or a Behringher, and the input channel trims are set to high and the clipping is occuring there. If it clips on the input stage, no amount of gain twiddling after the fact will get rid of the clipping.

John
johnmeyer wrote on 4/24/2007, 1:36 PM
1. Is the output of your camera balanced or unbalanced? What is the input connector in the auditorium console?

2. Are you going into a line input or a microphone input in the auditorium?

3. Does your camera have manual volume controls which affect the output?

4. What impedance is the input on the board? A bad impedance mismatch could cause problems.

farss wrote on 4/24/2007, 1:46 PM
If you're feeding this into a real cinema sound system, trust me, anything is possible. Most likely your audio is being fed into an input on their Dolby system. The system needs to be configured so that it knows that input is stereo else all hell can break loose.

All the cinema sound systems I've worked with have a Minidisc player, follow it's leads into the Dolby system, should be RCAs, unplug these and plug your DV deck into there. You may also need to disable the Dolby system from the AMX control. I've yet to find a cinema sound system that uses balanced audio by the way, all the 'serious' audio is digital. There maybe balanced for the optical track but it's on a DB9 connector so it's anyones guess as to what it really is.

Also be warned the Dolby systems I've had to struggle with use auto input switching, make certain you disable this if you're using a mic through the system as well. Had some really funky issues during a screening when a mic was left open near the screen.

Bob.
kunal wrote on 4/24/2007, 1:47 PM
I forgot to mention that the tape's being played from a deck (not a camcorder). I'm not sure about the impedance levels. I'll have to check that with the theater tech guy.

Either way, going by both of your comments, it sounds like it's quite likely a playback issue, as opposed to a problem in the source sound mix?

I'll try playing it in another theater just to confirm that. Thanks a lot for your help!
farss wrote on 4/24/2007, 2:02 PM
Would help a lot if we knew roughly what kind of system it's being fed into and how it's being connected. Is this a "theatre" as in live shows or a cinema, as in setup to screen movies from 35mm with surround sound?

Bob.
UKAndrewC wrote on 4/24/2007, 3:35 PM
If you have normalised the audio on your video to 0dB that could cause the clipping. If that is the case reduce it to -3dB if it is normal voices etc, or -1dB if it's got loud parts.

For digital use on CD and DVD, 0dB is maximum, for analogue 0dB is saturation.

Andrew
TheHappyFriar wrote on 4/24/2007, 7:05 PM
capture the tape to make sure it's ok.

i'm surprised the theater guys don't know what's going on.

can't really add anything that hasn't been said. like said before, something is amping your sound. now you just have to find out what & reduce it.