Need help with AC-3 encode error

[hummerZ]

I am experiencing a problem where a particular audio source is causing errors during the process of encoding to AC-3. Sounds fine in Pro Tools, but the AC-3 file is riddled with digital ticks. Different encoding methods produce identical results... (hardware and software)

Has anyone ever experienced anything like this? How about a potential solution?

Thanks!

[Doug the Brit]

Starting with the obvious....

Your source file is 48 kHz?

-Doug

[hummerZ]

Yes, 48 kHz. Complete Main, 1.0, no compression, 192kbps, dialnorm -31, no de-emphasis... pretty much standard settings, same that have worked on hundreds of other encodes.

The encoder works fine on other sources. It's something about this source that is causing the encoder to glitch.

[Craig F]

non-dithered mixer is being used right?

[hummerZ]

in protools? yes, standard stereo mixer.

[Postman]

Originally Posted by hummerZ

Yes, 48 kHz. Complete Main, 1.0, no compression, 192kbps, dialnorm -31, no de-emphasis... pretty much standard settings, same that have worked on hundreds of other encodes.

The encoder works fine on other sources. It's something about this source that is causing the encoder to glitch.

Interesting...a mono file. Are the glitches throughout, in loud and soft spots? Have you chosen the option to hipass at 10hz? Can you post an example somewhere?

[KK Proffitt]

What happens when you try dual mono 2.0?

[hummerZ]

Glitches are fairly consistent through the entire file, but don't seem to correlate with loud or soft spots in particular. Hi-pass and DC filters have been toggled to no avail.

Have not tried dual mono, but why would that change anything?

I will post an example tomorrow.

Thanks very much for the assistance thus far.

[KK Proffitt]

Originally Posted by hummerZ

Glitches are fairly consistent through the entire file, but don't seem to correlate with loud or soft spots in particular. Hi-pass and DC filters have been toggled to no avail.

Have not tried dual mono, but why would that change anything?

I will post an example tomorrow.

Thanks very much for the assistance thus far.

Although 1.0 saves space there have been a lot of discussions about the relative "goodness" of mono experienced via dual speakers rather than through the center.

A test of 2.0 would test the encoder, rather than the file itself.

[hummerZ]

yeah... um. we don't do the dual-mono thing. Listeners can change that at home, to their preference.

Anyway, if anyone is searching for a solution to this in the future.. The only way I've found to get rid of the problem is to *steeply* low-pass the source. Luckily for me, you're not missing much above 10k in this source.

However rarely it may happen, I must admit that I'm very bothered by the fact that the Dolby encoder can be tripped-up so easily.

Thank god for PCM on Blu-ray.