Film-Tech Forum ARCHIVE: Bizarre IMAX sound problem

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Posted by Jason Whyte (Member # 1433) on 04-30-2007, 01:31 PM:

Hey everyone,

I went to view "Deep Sea" at the IMAX in Victoria, BC this weekend. Towards the end of the film, the sound began to skip and repeat, akin to the needle skipping on a record. The rock-steady picture continued on just fine, but a line of narration played over and over again.

At first I thought it was a strange attempt by the filmmakers to beat one particular point in the film, but it kept going on for a good few minutes, until someone near the exit doors went to complain and the sound went back in sync quickly after.

Comp tickets were offered and apologies around, but there was no explanation by the management as to why it occurred.

I'm a bit limited on my IMAX tech knowledge (I'm far more experienced in 35mm projection) but this has been bugging me ever since I saw it. I have a few theories, but I'm hoping anyone can shed some light on sound tech in IMAX theaters.

Jason

Posted by Chris Slycord (Member # 4239) on 04-30-2007, 01:51 PM:

http://www.in70mm.com/newsletter/1997/50/tbp/sound.htm

According to the above they use a dubber for IMAX.

Posted by Ben Wales (Member # 92) on 04-30-2007, 01:58 PM:

Sounds they have a issue with the Audio (Hard Disk)Drive or File with the sound track on the Sonics DPP or DTAC depending what system they are useing.

Posted by Bobby Henderson (Member # 840) on 04-30-2007, 02:12 PM:

Most modern IMAX theaters are equipped with one or more digital surround sound formats, usually the IMAX DDP system using 3 compact discs for 6-track uncompressed LPCM audio playback. Some IMAX movies have also used DTS (in conjunction with the 70mm time code reader). Not sure what format is used on the DMR features that typically run longer than the 74 to 80 minute capacity of a compact disc.

The error being described during Deep Sea sounds pretty odd. If it was a normal CD scratch error then the repeating nature would have been a much faster, rapid (almost reverberating) kind of thing. I strongly doubt such an error would occur with the old fashioned 6-track full coat magnetic film strip audio system. Maybe some other piece of equipment in the audio chain fouled up. I don't know if any IMAX theaters employ use of rack mount digital delays, but that would be one thing I would automatically suspect.

Posted by Mark Gulbrandsen (Member # 72) on 04-30-2007, 05:17 PM:

quote: Bobby Henderson
Some IMAX movies have also used DTS (in conjunction with the 70mm time code reader).

This was for only one film(Disney) at one location(Spokane). There have been other trials and experimants though nothing for the long term. Thanksgiving Point 15/70 system is also DTS capable and can playback DTS reading the time code from the print although they have never done so yet.

Mark

Posted by Dick Vaughan (Member # 540) on 05-01-2007, 02:54 AM:

Most "modern" i.e post 1998 - pre 2005 IMAX theatres use the DTAC sysytem. The soundtrack is loaded from DVD on to the hard drive of the system and played back from there under normal circumstances. The 3 disc DDP system was superceded by this.

Unfortunately the DTAC is basically a NT based system using P1 processors which sometimes " throw a wobbly" especially if the CPU temp gets a bit warm.

quote: Chris Slycord
According to the above they use a dubber for IMAX.

That is an old article , 1997, about a theatre that opened in the late 80's . We all ran dubbers or 8 track 1/2" back then.

After our 1999 upgrade to 3D we had a DTAC based system installed but retained our dubber for library prints. I think we have maybe run it 50 times in 8 years .
This looping is a fairly well known phenomena.

Posted by Jason Whyte (Member # 1433) on 05-01-2007, 12:00 PM:

Thanks for all the responses.

quote: Bobby Henderson
The error being described during Deep Sea sounds pretty odd. If it was a normal CD scratch error then the repeating nature would have been a much faster, rapid (almost reverberating) kind of thing.

That's also what I was thinking. The "skipping" sounded pretty seamless, as the line that narrator Johnny Depp said with a soft music score in the background actually sounded somewhat natural!

Jason

Posted by Adam Martin (Member # 641) on 05-02-2007, 12:18 AM:

See this thread also.

Posted by Thomas Pitt (Member # 4322) on 06-07-2007, 03:31 PM:

There also seems to be a different sound problem in the Bradford IMAX recently. Instead of the digital sound playing, a really loud buzzing/grating noise comes out of the auditorium speakers. It sounds rather like when you try to play a CD-ROM disc on an audio CD player (one that doesn't mute data tracks)

This can happen right from the very beginning, when the announcer says "Ladies and Gentlemen, you are about to experience..." etc. It can also happen part-way through a film.

It happened today with the showing of Dinosaurs Alive 3D - the loud buzzing noise came through the speakers every time they tried to play the opening announcement! I also heard a very loud 'boom' from the speakers at various points when the technician was trying to fix it.
Part way through the film, the audio suddenly cut to this noise again; but this time they were able to fix it in 15 seconds (during which time the film was playing silently).

I'd say there was something wrong with the decoding of the digital audio streams. Anyone else heard that kind of error in IMAX or DTS sound systems?

No refunds for this performance, although they compensated by not running the 35mm ad reel before going into the IMAX film [Razz]

Posted by Dick Vaughan (Member # 540) on 06-08-2007, 03:36 AM:

Thomas

The noise you heard is asoociated with the Digital -analogue conversion.

We had a similar problem a couple of years ago and in that case replacing the SCSII cable between the DTAC and the IDAC solved it.

The problem reappeared on Tuesday for 4 shows but was not present after 4pm. Wednesday we had no problems at all . The show you were in was one of two affected yesterday.

As with all intermittent problems they are a sod to sort out.

We are able to clear the problem on most occasions by "Stop/ Starting" the show on the DTAC which is what happened in the middle of the show. However at the beginning during the announcements this didn't work and we had to shut down the show and reboot the DTAC.

Still investigating various components in the D to A line and at present , fingers crossed, it's running ok.

Sorry that your experience was spoilt.