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Are These Digital Audio Compression Artifacts? Why?
glenndale
post Feb 13 2012, 20:58
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I've been hearing it for months now, as have many others, regardless of network.
It's a metallic ringing, usually right after loud audience applause, or certain music that builds to a crescendo.

A couple of examples:
http://www.youtube.com/watch?v=XCV-kudNo98
http://www.youtube.com/watch?v=xh9E8QPowSQ

Can someone verify it's compression artifacts?

And, if so, why is it getting by the networks?
Can't they correct the problem?
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saratoga
post Feb 13 2012, 21:06
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Where in those tracks should i hear ringing?
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glenndale
post Feb 13 2012, 21:17
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QUOTE (saratoga @ Feb 13 2012, 22:06) *
Where in those tracks should i hear ringing?


:12 and :17 in 1st
:02 and :07 in the 2nd, bit more faint than the 1st.
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Ethan Winer
post Feb 13 2012, 21:54
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QUOTE (glenndale @ Feb 13 2012, 15:17) *
:12 and :17 in 1st


I listened only to this first example. That's not an artifact, it's part of the sound track music. Now, whether that's really how it's supposed to sound is another matter. I noticed the audio is generally swishy sounding due to lossy compression.

--Ethan


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mixminus1
post Feb 13 2012, 21:56
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Definitely not a compression artifact - it's some kind of generated sound (a metallic or synthetic-sounding "buzzing" might be a better way to describe it).

Whether it's intentional (as some kind of watermarking) or an artifact being generated somewhere in the broadcast/distribution chain, I can't say, but it isn't a lossy compression artifact.


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mzil
post Feb 13 2012, 23:06
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Interesting. People who have listened to just the first example need to go back and listen to the second example. It is exactly the same little "melody"!

It reminds me of the familiar sound of an old school telephone modem making contact and sending its burst of digital communication when it is first establishing a link. Not exactly the same, but analogous, perhaps.

This is a good mystery. I'm subscribing.

Maybe we found Cinavia! Yuck-yuck.

Are the only people hearing it using over-the-air TV or do satellite and cable folk hear it too? Are there known DVD's that have it? That would establish if it is transmission related, maybe.

This post has been edited by mzil: Feb 13 2012, 23:10
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glenndale
post Feb 14 2012, 00:11
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Personally I've noticed every single night on Letterman. But only when the audience gets loud.

Have also have heard during football games when the crowd gets very loud. And things like the Emmys.
Then again, not every broadcast is this noticable. But it happens many times only during audience or crowd applause/cheering, so I don' think it's injected watermarks.
And it's been reported on Verizon and Comcast at least, not sure about OTA.

This post has been edited by glenndale: Feb 14 2012, 00:20
Reason for edit: removing unnecessary full quote of above post
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christopher
post Feb 14 2012, 02:03
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You have good ears to have picked that up during Fringe, I didn't notice it at all (although admittedly my brain wasn't keyed in to notice the sound).

That sound constantly on broadcast would piss me off royally. Hope you find out what's causing it. Will keep tabs on this thread.


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Kujibo
post Feb 14 2012, 02:38
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I'm not even sure I hear it as I have nothing to A/B it against, but if it's only happening after things get loud I might wonder if it is some poorly implemented compressor/limiter inserted in the broadcast chain that is pumping the gain in some weird way as it returns the gain back to normal after reducing it for the loud section. Poorly implemented gain changes (jumping abruptly instead of ramping over time, or outright bugs) can cause "zippering" effects that may sound something like what you are hearing.

I'm too lazy to do it but I might even guess that if you imported that audio into an editor you might be able to identify a frequency to the noise that may indicate the block size the audio is being processed at (e.g. 187.5 Hz if every 256 samples at 48 kHz). That for me would be a dead giveaway that there is some problem with the limiter/gain algorithm/implementation.

Anyway, just a guess.
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mzil
post Feb 14 2012, 04:44
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QUOTE (glenndale @ Feb 13 2012, 18:11) *
Personally I've noticed every single night on Letterman. But only when the audience gets loud.

Have also have heard during football games when the crowd gets very loud. And things like the Emmys.

See if you can spot it in something that is rebroadcast again later in the week, unlike Letterman, sports, and the Emmys. Then you can tell the rest of us "Listen for it at 15m 30seconds into the movie Titanic on TBS", or whatever, and we can see if it occurs in our cable systems as well, or is only in yours.
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C.R.Helmrich
post Feb 14 2012, 23:59
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Same sound, right? http://www.youtube.com/watch?v=JCWEzfbPlfk

I'm with mixminus1, two things come into my mind: electromagnetic interference prior to encoding/broadcasting (likely), or problem with the encoder hardware (unlikely, I've heard artifacts like this before due to faulty memory, but they were much more noticeable). Edit: hmm, in all three videos it occurs periodically... on a 5-second grid...

Chris

This post has been edited by C.R.Helmrich: Feb 15 2012, 00:08


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glenndale
post Feb 15 2012, 13:38
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QUOTE (C.R.Helmrich @ Feb 14 2012, 23:59) *
Same sound, right? http://www.youtube.com/watch?v=JCWEzfbPlfk

I'm with mixminus1, two things come into my mind: electromagnetic interference prior to encoding/broadcasting (likely), or problem with the encoder hardware (unlikely, I've heard artifacts like this before due to faulty memory, but they were much more noticeable). Edit: hmm, in all three videos it occurs periodically... on a 5-second grid...

Chris


haha yep, do do do do do do.

but it's not a timed event. it's during the loudest part of clapping, cheering, music, etc.
that's how I understand a problem in the compression algorithm that produces this digital artifact, but what do i know?

any broadcast engineers out there?
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slks
post Feb 17 2012, 10:35
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I wasn't able to identify artifacts in any of these clips. I guess that's a blessing.

However, it's very possible for artifacts to pop up. I think all broadcast TV is now digital, and so goes through compression. I remember hearing compression artifacts very clearly on my AT&T U-Verse service - it occurred on sibilant sounds like when people say words with 'S' in them. They seem to have fixed that though, I haven't noticed it in some time.

So when you watch a clip on YouTube, it's most likely gone through several rounds of lossy compression - First being compressed for the broadcast, then possibly re-encoded to store on a computer, then encoded a third time by YouTube. Lossy-to-lossy transcoding is a big no-no for audio quality. Stuff on YouTube is often very mangled, with clear artifacts, after having gone through so many rounds of compression.


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hlloyge
post Feb 17 2012, 10:56
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Well, I doubt these are compression artifacts, my guess is it's some signal for copy protection, or for auto loudness control, or... mind control smile.gif just joking.
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