3 Lip-Sync Error Delay Units
Published on July 10, 2007
Primare Delay Box
0 – 600ms digital delay
Full conversion between coax & Toslink
Made in Sweden
U.S. Distributor: Sumiko
Felston DD740 Four-Input Digital Audio Delay
SRP: $249 (£159.80)
0 – 680ms delay (340ms for 96K signals)
Either 1ms or 1/3ms steps
36 preset delays
remote with numeric keypad for discrete delay entry
discrete input switching
full conversion between coax & Toslink
4 digital audio inputs, 2 digital audio outputs (Toslink & coax)
Adjustable display brightness
Alchemy2 D2L Digital Delay Line
Signal format: SPDIF
Delay Range: up to 1.4 seconds at 44.1K, proportionally less as S-R increases
Connectors: 1 ea. RCA in, Toslink in, RCA out, Toslink out, 2.5mm DC power jack, 3.5mm RS232 port
Comes with wireless remote and HDTV Calibration DVD
Weight: 1 lb.
3533 Old Conejo Rd., Suite #107
Newbury Park, CA 91320
Back in the early days of PBS network carriage of classical concerts, the stereo audio feed was sent by an entirely different path than the video from the east coast to the west. As a result the voices coming out of singers in an opera had little relationship to the movement of their mouths for those of us viewing the program on the west coast. I don’t recall now if the sound was ahead of the images or lagged behind it; I just recall it was terrible and ruined appreciation of the concert. And there was nothing to be done about it.
Today we have an increasing number of home theater viewers running into a similarly frustrating lip-sync problem. It is never a situation of the audio lagging behind the video but always the reverse. There have long been slight discrepancies in lip-sync with certain video material but it usually has been so slight that it remained under the radar of the average viewer. What has exacerbated the problem for many is the purchase of their first flat-screen HDTV display, which carries out varying amounts of video processing, thereby delaying the image behind the sound. The DTV channels also process their images more than the analog channels, and upsampling DVD players and displays do more video processing in order to display a higher-resolution image. I myself was seldom bothered by lip-sync inaccuracies with my former Pioneer CRT display, but my present Samsung DLP display made it an immediate concern. Unfortunately, the Samsung DLP and LCD lines suffer from a more serious delay due to video processing than most other displays, and the firm appears to not have a fix for this design flaw. Sony had a similar problem with several generations of displays, but one authority reports online that “this is now a non-issue.” I beg your pardon – just having it corrected in a display doesn’t solve the overall problem! There are many different causes of lip-sync losses than would still cause them to occur on a supposedly-corrected display.
Possible Causes of Lip-Sync Problems
• The original film or video production was careless about sync.
• The network distributor of a telecast processes both the video and audio, but the video processing delays the image so it lags behind the sound.
• The local station processes the video, delaying it further.
• The satellite or cable service processes the video as part of its data reduction to fit in as many channels as possible.
• Your own DVD player and/or HDTV display processes the video – whether upsampling or converting from interlaced to progressive or not.
• Errors can be made during the DVD authoring process.
• If you have an outboard video scaler, its processing can cause video delays.
• If you run your video thru your AV preamp or receiver which upsamples and/or converts the signal, that can delay the video.
• The increased video processing used with HDTV only makes things worse.
Your reaction to all of this might be “Why not just use the audio delay adjustment offered by most AV preamps and receivers today – and by some DVD players and displays as well?” (Some manufacturers confusingly term this feature Video Delay.) Well, the reason is that the amount of delay in the image that puts the audio ahead of it varies all over the map, can vary for different video sources, and can even vary during the course of a film or program. You can’t go deep into the menu of your display to change the audio delay every time you run into a lip-sync problem. My Integra DPL 10.5 uni player allows three different settings for what they call the “time difference between image and audio,” but they are difficult to select, you must still go part way into the menu using the remote to choose the one you have set for a particular input, and none of the settings are ever just right for what you are watching. The latest version of the HDMI all-in-one digital cable (v1.3) has just been announced as solving lip-sync errors; it’s impossible for just a cable to do that – it depends on the components at both ends of that cable! And there’s no way they could solve it for program sources that vary in the amount of lip-sync error. Even some $20K front video projectors have had lip-sync problems. That’s why a dedicated dynamic lip-sync correction device whose delay time can be instantly increased or reduced is required.
Before we get into the little black boxes that can solve this dilemma, let’s summarize some of the research that has been done on the phenomenon. First, we are all well used to situations in which the image is seen prior to the sound of an event. We just had one on the Fourth of July – a distant fireworks explosion is often seen a split second or longer before we hear its sound. That’s doesn’t bother anyone.
However, the brain has a difficult time getting around the sound being heard before the image making the sound. That’s an impossibility that’s hard to confront. Stanford University did some research on a statistical link between negative viewer perception and audio leading a sound that is pictured. People vary in the amount of such delay which they notice. The Stanford tests used about 50ms of advanced audio, which most of the test subjects failed to notice. But beyond a certain length of delay – say 75ms – most people become conscious of the lip-sync being off.
The Stanford experiments found that out of sync audio interfered with viewers’ perception. The viewers had less “trust” of a talking head onscreen when the audio preceded the video, even though they usually couldn’t provide any reason for their feeling that way. Another theory might be that most people haven’t been exposed to lip-sync errors high enough to break their defense mechanism and cause them to notice it, but when they are they can become sensitive to very low errors – such as only one video frame (33ms to 40ms). Just as a certain percentage of the population cannot see 3D images with the proper glasses or viewers, and a similar percentage cannot hear binaural surround sources with headphones, some people are oblivious to loss of lip-sync unless it is really gross. The broadcast and electronics industries in general don’t seem concerned with this problem, so it comes down to the sensitive end users to correct the problem for themselves. If it is frustrating you now there is only one real solution – one of these black boxes.
One of the leading HT reviewers said in his review of just one of these three units that “there’s very little else like it on the market.” Well, it didn’t take me much Googling to discover there are at least three to choose from, and there may be others I don’t know about. (There is another, but at about $200 it sounds too basic, lacking a remote control which would be absolutely vital to useful operation.)
All of these units accept both optical and coaxial inputs and outputs and have separate inputs for your different video sources. You can go in with coax and out with Toslink if you wish – the units all convert. I ran separate cables for the audio from my Samsung HDTV display, my Integra DVD player, My Pioneer Blu-ray player, and my (don’t laugh) Betamax player on the two brands I evaluated. Keep in mind that these boxes operate on the digital bitstream signal – not the analog. Therefore if you use the six-channel analog out of your DVD player for the uncompressed PCM 5.1 option on those hi-def DVD that have it, you will not be able to use the digital delays. You must go thru the digital or Toslink single-cable connection.
There are individual features each unit has, but I don’t think they are as important as the basics of having a wide range of delay adjustment easily made from the remote, and the digital delay being transparent, with no deterioration of the audio quality. One of the makers calls it “bit-perfect reproduction” and all three claim it. The Alchemy2 has be far the largest delay time – probably way beyond what one would need. 600ms or so should be plenty for most all situations. The Felston is unique in offering not just 1ms increments but with a flick of the wrist you can tweak them down to 1/3ms increments. Frankly, I couldn’t tell the difference with such minute changes, but more power to those who are attuned to it. All three remotes have + and – buttons to increase or decrease the delay, and a clear and bright digital delay display so you know exactly what you are getting. And all three have a Bypass button for instant comparison of the undelayed signal with the delayed. They also all handle both 48K and 96K sampling rates. The Primare automatically goes into Bypass mode when you play a 44.1K source. Some also have a numeric keyboard and even present delays so can instantly recall the setting for a particular source if you wish. The Primare is the largest, though still a very small black box, and the Alchemy2 is the smallest.
I had already noticed that the lip-sync error varied on some programs and even on some DVDs, but working with these audio delays I became even more aware of the maddening problem’s ubiquitousness. On a George Carlin DVD I had to use a 45ms delay to correct the lip-sync error – at least it was consistent from beginning to end. Where it seems to vary most and be the worst is programming from PBS – at least here on the west coast. A public TV engineer explained to me how PBS uses much more digital data reduction in their network transmissions than the commercial networks, and how that results in pixilation artifacts – such as when a Ken Burns-type still photo crossfades into another still photo. Everything can break up into tiny squares at that junction. Well, along with the image quality going to hell in a handbasket, so often does the audio delay. Now, if I’m willing to work that remote a bit, I can finally enjoy my Novas and Dr. Whos without cursing.
Your choice of which delay to purchase should consider the various features and pricing. I found the Felston did the job beautifully but I’m sure either of the other two would give you a leg up on controlling lip-sync from now on and enjoying your video viewing more. The first two brands offer more than one model, so you should also check the specs of the alternative versions.
- John Sunier