Audio issue with DCP-o-matic

[Peter Foyster]

My advertising slides DCP is made up in DCP-o-matic. The slides themselves are .png files of 20 seconds duration. There is a light music track set at around -20db RMS as a background to voiceovers for each slide, each set at 20 seconds and peaking at -10db.
I noticed when making up the new slide program, the voiceovers are muffled, distorted and indistinct. If I remove the background track the sound is fine.

I have never had this issue in the past, the music track played quietly behind the voiceovers.

I am using version 2.16.14. Is this a glitch in dcp-o-matic or do I have an incorrect setting?

[John Thomas]

What do you have for the "Processor" setting in the DCP->Audio section?

There was a fairly recent bug where the gui forced an audio processor and didn't give a "none" option. This was fixed in 2.16.32, so definitely update to the latest and try again. It's an easy enough first thing to try.

[Peter Foyster]

Processor is set to 'None'

In the Gain Calculator it is set to 'Dolby CP650 or CP750'.

When making the DCP I was getting warnings that the gain was too high on the centre channel so I set the peak level on each audio file to under -10db.

Although the warning went away the problem still persists if I add the other audio file. Funny, I never had this problem before, regardless of the peak level settings.

I guess I can try updating and see what happens.

[Peter Foyster]

I updated to the new version of DCP-o-matic, however the problem persists

[Carl Hetherington]

Is it possible to upload the pcm...mxf file from the bad DCP somewhere so we can check it out? I can give you an account on https://dcpomatic.com/send/ if that's the easiest.

[Peter Foyster]

Thanks Carl,
That would be much appreciated

[Carsten Kurz]

How do you actually create and assign separate audio for background music and voiceovers? I assume, the background music goes to left and right. The voiceover, if contained in a separate track, should probably go to center. It is possible, through, that you sent them to the LFE channel. That will result in very muffled sound. Assuming that you use an LFE at all. Also, sometimes voice is recorded on two channels stereo-like, but has issues like phase inversion. That could result in muffled sound as well.

Did you check the DCP audio with DCP-o-matic player?

As you are making just 20s slides, I guess it's no big deal to upload a whole dcp-o-matic project folder. That will give us a better idea about how the project is set up. Please include the picture and audio files as well. We don't need the DCP created in that folder. Just the project folder with settings, and source files.

[Peter Foyster]

Thanks Carsten,

This is the first time in the roughly seven years that I have been creating the project in DCP-o-matic that I have encountered this issue.

The voice-overs are professionally recorded and provided to me as WAV files.
Each WAV file is exactly 20 seconds in duration to match the slide run time.
The voice is assigned to the centre channel and the peak level set to -10db. I do assign the voice to L and R also at a lower level to get the coverage. It is an outdoor venue and the sound quickly dissipates into the air.
The music background is assigned to L and R by default and the peak set at around -20db.

I have remade it completely with just the voice, which sounds fine, but as soon as I add the background music the sound becomes all distorted and unintelligible.

I believe that Carl is looking into it as I sent him the PCM file last night.

The picture and audio files combined would be quite huge. The project folder itself is 29Gb.
I have made a cut down version with just 3 slides and voiceovers and the background music. The problem is still there. Can I send that? The folder size is 1Gb

[Carl Hetherington]

Hi Peter,

Thanks for sending the MXF - the problem seems quite strange - the audio for the voice-over is being broken up into bits for some unknown reason. This cut-down project that you've made would be very helpful. You should be able use that same dcpomatic.com/send site to send it, if you like (or feel free to use some other service if it's easier).

[Carsten Kurz]

Is the background music track MP3 or WAV? If MP3, you could try to convert it to a WAV file first (e.g. with audacity). Every now and then I come across MP3 files with strange format extensions (like internal video tracks), or strange sample rates/bitrates.


Anyway - Carl will be interested to see the project file. I just created a test the way you described it - stereo background on L/R, and mono voice on Center, -6dB on L/R, and that works the way it is intended (DCP-o-matic 2.16.32), so, the matrix/mixing in the current version does seem to work as expected. But in this case, all audio was WAV and 48KHz.


Do you hear the broken sound already in DCP-o-matic while previewing the project, in DCP-o-matic player checking the final DCP, or on your cinema server/audio system?

[Peter Foyster]

All the audio files are WAV. As I mentioned, I have been creating and modifying this project for near on 7 years without major issues.

The broken sound on the voiceover audio happens when I preview in dcp-o-matic and when I create and play the DCP on my PC using dcpPlayer.

I am thinking that the fault probably lies within my system but need to explore all possibilities.

The only major change would be that I upgraded the PC on which the project is created, from Windows 7 64 bit to Windows 10 64 bit.. Perhaps Carl will find something in the project file that will explain the issue. I will try to get that uploaded as soon as possible.

I have another project using several mp4 videos, including a voiceover added to one of them in dcp-o-matic, and that works perfectly.

[Carl Hetherington]

Hi Peter, Thanks for sending the files! It's a bug in DCP-o-matic - I'm working on it... I'll let you know when there's a new version to try.

[Peter Foyster]

Thanks Carl,

I seem to be having a bad run with bugs lately.

[Carl Hetherington]

Hi Peter,

There is a Windows installer here: https://dcpomatic.com/temp/2368-bad-sound/7592f3d/

which should hopefully fix your problem. Let me know how you get on... I'll make a proper "release" with this fix if it works for you.

[Peter Foyster]

That certainly seems to have fixed the problem. Cheers Carl. You are a genius!!