Audio on modern plane in-flight entertainment. Why does it sound like it's on tape

[smurfer77]

I've noticed a few times now that the audio of the on demand movies can wobble in pitch like a stretched tape. The last flight I took was one of the worst ever, and it was on a new 787 (Air Canada).

Is it just a simple cast that the processing demands are high compared to available processing power and instead of doing audio-visual dropouts, the system adjusts speed and catches-up and short time scales that effect audio in this manner (something that might not be that noticeable visually but our ears are sensitive to changes in pitch)? Or it's something completely different? Can someone knowledgeable on this fill us in, because it's driving me crazy!

Cheers

 

[restorer-john]

There's a bit on the internet about the Panasonic system used getting the audio out of sync.

I'm gonna say it before anyone else does- maybe it needs recapping? haha.kidding.

 

[smurfer77]

haha, yeah, it may indeed just need a recap, and probably some deoxit. Seriously though, if it was just out of sync, that would be better ... but the audio pitch goes up and down, and I have a sense that I need to take the tape and bake it to remove some moisture

 

[Pioneer!]

"In flight, the four engine generators are the primary sources of electrical power; the APU generators are secondary. Power runs from the generators to four alternating current (AC) buses, where it is either distributed for use as is (235 V AC) or converted to what other systems need." -Boeing

Said generators are attached to the engines.

It might have something to do with actual power output, as DC systems are run off of a Transformer Rectifier Unit. Depending on the quality these may have less clean power than others.

That said, I don't know much about plane electrics, and just did a bit of cursory research.

On the electronic side of things, the video/networking system could be grossly underpowered for the task it is performing, and a buffering issue may be present in that system. My personal guess is that they may not have fully accounted for the real-world load when they designed it.