Sound System 'POP' after homemade trailers

[Leo Enticknap]

Opening up the track in Audacity as Carsten recommended, it looks like all 8 channels fall to '0' before the clip ends.

Then the problem isn't in the DCP.

[Jacob Tutt]

Hmmm. So would that point towards a playback issue in the IMS2000?

[Marcel Birgelen]

What's the bitrate of the audio tracks in your home-brew DCPs?

Maybe the IMS2000 doesn't like to switch sample and bit-rates inter-DCP and the re-initialization of the audio-renderer to this new sample and bitrate puts some garbage left in some buffer out to the DACs.

DCPs default to 48,00khz at 24-bit, if you're not encoding to this sample/bitrate, have you tried to up- or downsample to that rate?

[Carsten Kurz]

DCP-o-matic makes sure all output is 48KHz/24Bit. Unless he is using a very old version which would allow 96KHz if source had that rate.

But it could also be the audio channel count, as homebrew DCPs will often be 2ch.

[Jacob Tutt]

We are using DCP-O-Matic version 2.14.37

Right now the recurring issue is happening between a 'homebrew' 7.1 ch snipe, and 3 seconds of black where the CP750 switches back to 5.1 and sets a specific volume level before the feature starts.

Could switching from 7.1 to 5.1 (or reverse) be causing the blip?

[Frank Cox]

You could easily find out by sending a "set 7.1" cue to the processor, and then send a "set 5.1" cue to the processor and see what happens.

[Steve Guttag]

I've never known the CP750 to pop between 5.1 and 7.1 content. Early on, maybe between prologic and 5.1. CP650s have been known to have snats when things transition (content, not format).

[Leo Enticknap]

If the IMS2000 is still on 2.8.26, with media block firmware and security manager of a similar vintage, I would suggest updating all three to current as a next step. I do have a recollection of audio fixes mentioned in the release notes for recent versions.

To establish if this is coming from the media block or the CP750, you could do either of the following, if you have the equipment to do the experiments with:

- Connect the AES output of that IMS2000 to a different audio processor (ideally not a CP750, but another CP750 would give a clue as to if there is a fault with that specific CP750, as distinct from a hardware design or firmware bug that affects all of them), and hear if the fault reproduces

- Connect that CP750 to a different media block (not an IMS2000), and play the CPL through it that causes the fault when played on the IMS2000.