Around the World in 80 HD Advisors

Posted Fri Oct 22, 2010 at 11:00 AM PDT by

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Answers by Joshua Zyber

Audio Jitter

Q: I use a PS3 as my main media center. I recently was forced to switch from an original "fat" PS3 to a PS3 Slim since the fat one died on me. I began reading up on the differences between the two systems and found that the PS3 Slim produces more audio jitter when watching DVDs and CDs. What is audio jitter, and will it really affect the technical performance of the film? Basically, can I hear it?

A: Jitter is one of those things that audiophiles like to stress-out about. For the rest of us, in real practical terms, if you don't notice anything wrong then you probably shouldn't worry too much about it.

Any sort of digital data transmission, including audio, will be sent from source (Blu-ray player) to destination (A/V receiver) as a stream of 1s and 0s. Assuming the connection is sound, the destination should receive all of the 1s and 0s, and receive them in the proper order, thus allowing it to decode that signal. However, jitter is a variation in the timing of those 1s and 0s. Some may arrive just a little bit early, and others may arrive just a little bit late. If the jitter is severe, that can lead to audible distortion or degradation of the sound signal. Think of it like listening to an old LP on a record player with an unstable motor that randomly speeds up and slows down how fast it spins the disc. That's an exaggerated example, of course, but it may help to demonstrate how timing can affect the audible results.

In the past, I'd always been told that transmitting audio in PCM format was more susceptible to jitter issues than transmitting in either Dolby or DTS bitstream formats. Audio compression codecs (whether lossy or lossless) packetize the data and require clocking mechanisms in the receiver that should minimize or eliminate jitter.

However, this paper claims just the opposite, that bitstream transmission is more susceptible to jitter. Honestly, at this point, I'm not sure what to believe. I'll leave it to our audiophile readers to argue this out in the forums.

[Update: As pointed out by a reader, that paper was actually referring to data storage on the disc, not transmission method. My initial understanding was correct that "bitstream" transmission should not suffer from jitter.]

Early CD players and audio receivers that transmitted linear PCM over S/PDIF connections (either Toslink optical or digital coax) were quite prone to jitter, which is what launched so much consternation over the subject in the first place. Most modern equipment uses data buffers and clocking circuitry that should mitigate the problem. I'm not saying that jitter doesn't exist anymore or that no one can hear it. Let's just say that some people are more sensitive to it than others. Or at least claim to be.

Since you'd previously owned the old version of the PS3 and now have the newer PS3 Slim, I'd simply recommend that you watch a bunch of movies and decide for yourself whether you hear anything different or "wrong." If nothing stands out to you, then I suggest that there's no reason to stress about it. Just enjoy your movies.

Center Channel Volume

Q: I'm just curious as to what decibel levels above I should put my center channel speaker at? If I leave it the same level as my front and rears, then it's too low. I'm using a sound level meter.

A: Generally speaking, you should calibrate all of your speakers to read the same decibel level with test tones. Movie soundtracks are mixed in that fashion, and with the expectation that you will listen accordingly. However, it's very possible that acoustic conditions in your room may affect the audibility of dialogue from the center channel.

If your A/V receiver offers any sort of automated calibration program such as Audyssey MultEQ, it may be worth giving that a try. In addition to setting speaker volume levels, these programs often also adjust equalization settings to "correct" sonic problems in the room and improve audibility. While I'm not necessarily 100% sold on these techniques in all circumstances (sometimes this sort of fiddling with the signal does more harm than good), it may be worthwhile if you have a consistent problem hearing dialogue.

It's also worth noting that many modern movies (especially action and sci-fi movies, but not necessarily limited to those genres) are mixed extremely "hot," with (sometimes excessive) dynamic range that causes dialogue to be drowned out by music and sound effects. Last year's 'Transformers: Revenge of the Fallen' was a big offender in this regard. I find this tendency really obnoxious and grating. In these situations, you may find benefit in raising your center channel volume a little bit to compensate. But there isn't going to be one magic setting that will work for every movie, so you'll just have to set it to taste, and remember to change it back when the movie is over.

Homework Assignment: You Be the Advisor

The HD Advisor knows many things, but he doesn't know everything. Some questions are best answered with a consensus of opinions from our readers. If you can help to answer the following question, please post your response in our forum thread linked at the end of this article. Your advice and opinions matter too!

Vertical Stripes in 'First Blood' and 'Broken Arrow'

Q: I was recently watching the Blu-ray release of 'First Blood.' I noticed in some of the shots what appeared to be a series of several dozen vertical stripes of slightly higher brightness. It was most noticeable in the scene where Col. Trautman is first talking to Rambo over the radio. The shots with Rambo look perfectly normal, but the shots of Trautman inside the tent have these parallel, vertical lines of alternating brightness. I remember noticing the same thing on a number of the desert shots when I watched 'Broken Arrow' a little while back. However, I had watched the two movies on two different Blu-ray players (DMP-BD60K and BD-P1000 respectively), but on the same television. I didn't see any mention of the problems in the reviews of the movies, so I was wondering if there might be a problem with my television (a Panasonic TBM2AX03401). Is this possibly something on the source material, or could it be my setup?

JZ: Has anyone else noticed this problem with either of these discs?

Check back soon for another round of answers. Keep those questions coming.

Joshua Zyber's opinions are his own and do not necessarily reflect those of this site, its owners or employees.

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