Film-Tech Forum ARCHIVE: Audio jitter with Doremi IMB + JSD-100

This is topic Audio jitter with Doremi IMB + JSD-100 in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=16;t=002157

Posted by Mark Strube (Member # 4190) on 12-26-2014, 11:29 PM:

I've noticed a subtle problem on two screens. One screen has tri-amped stage channels, the other bi-amped, both have the crossover occurring inside the JSD-100, and both auditoriums are 7.1. (Both films are currently running in 7.1.)

When certain musical notes are hit in the audio, I notice a jitter effect, not unlike what a glitchy film-based Dolby Digital soundtrack would sound like. An example would be much of the music in the end credits of Hobbit 3... or the initial musical notes from Night At the Museum 3.

It sounds like some sort of on-the-fly sample rate or speed conversion is happening... don't know where that would be coming from though. Any ideas?

Posted by Harold Hallikainen (Member # 5405) on 12-27-2014, 12:14 AM:

Interesting! The JSD-100 DSPs run at 96kHz, so there are sample rate converters on all inputs. But, I've never heard of this issue. I wonder if some of the musical frequencies are landing on the crossover frequencies and that you're hearing the sound shift from one band to another or perhaps hearing comb filtering due to the different physical location of the drivers. Just guessing, though. I THINK most servers (and correct me if I'm wrong) can be set to always output 96k (always sample rate convert), always output 48k (always sample rate convert), or to be transparent (never rate sample convert). How is the server set? Also, I always wonder about effects of forensic marking.

Interesting issue. I look forward to hearing other comments!

Harold

Posted by Joe Elliott (Member # 4006) on 12-27-2014, 02:28 AM:

Also what version of firmware are they running. When the JSD-100 first came out, it had some pretty buggy firmware. Has it been updated since install? Some PM contracts don't include audio updates or work above a simple audio check, so it may be likely that they haven't.