Almost anyone with a digital projector, LCD TV, or plasma TV will notice that the picture and the sound are not always in synch. This becomes most apparent in close-ups when lips do not move in exact time with the sound. This phenomenon is particularly common if you are sending the video signal to a display device, and the audio signal to a separate AV receiver. The reason it happens is simple: There is much less digital processing required to deliver an audio signal to a speaker than there is to deliver a video image to a screen. So the sound often gets to your ears before the picture gets to your eyes.

When audio arrives slightly ahead of video, it is annoying to say the least. It creates a sense of unreality that limits your ability to immerse yourself in the material. The human mind can accept video ahead of audio, since that happens in the real world all the time-you see the lightening before you hear the thunder. But when sound arrives before you see the event that caused it, the brain gets confused. Instead of concentrating entirely on the drama at hand, you are subliminally aware of the fact that the lips are not moving in time with the sound track.

When this happens you get distracted. You try to figure out if it's a chronic problem or a temporary aberration. You wonder whether you will notice it again in the next scene as much as you did in the previous one. This semi-conscious brain chatter is going on while you are trying to concentrate on the movie. So your ability to enjoy the big screen home theater experience is short-circuited, quite often without you even being aware of it. When audio and video are not in perfect synch, the whole experience is less "real" and believable.

The solution is to introduce an audio delay into the system. You might already have an audio delay feature on your AV receiver or external video processor. This can address the problem to some degree, but often not with the precision you really need. A more comprehensive solution is available with the use of the Felston DD740 Audio Delay. It is a little component selling (at the moment) for an introductory price of just $199, and it's a great way to get lip synch problems eliminated from your home theater.


The DD740 is a tiny black box that does just one thing: It introduces a small timing delay in the transmission of the audio track. That delay brings the audio back into synch with whatever video you are watching.

Not only is the DD740 small and inexpensive, it is as simple as a home theater component can get. Instead of running your audio cable from, say, your DVD player directly to your AV receiver, you plug it into the DD740, and then run a second audio cable from the DD740 to your receiver.

Once the cables are connected, you power it on and presto, you have an automatic default audio delay of 100 ms (or one-tenth of a second). That compensates for a three-frame delay in video delivery. Now, for any given combination of video source and display products, a 100 ms audio delay might be just right. However, video sources and display systems will vary in the amount of the video delay that they produce. So you can adjust the DD740's delay time up or down via simple +/- buttons on the remote. This allows you to bring the sound and picture into perfect synch.

The Felston DD740

The adjustment range is from 0 to 680 ms for a 48 kHz audio signal, and 0 to 340 ms for a 96 kHz signal. But even 340 ms is ample delay time to compensate for the most complex video processing-that's about one-third of a second, which would be equal to a ten-frame video delay. In normal mode, the delay can be changed in increments of one millisecond, but there is a fine tuning mode that lets you step incrementally in 1/3 ms. Frankly, we have no idea why consumers would need that sort of fine tuning control, as the ability to step in one-millisecond increments is ample control for us. But this is Felston's third generation audio delay product, and the company says this fine tuning feature was added because users of the earlier generation products requested it. In any event, the system gives you as much control over the actual delay on any input as you'll ever need, and far more precision than you're likely to get from your AV receiver or video processor.

A Key Advantage

Perhaps the most important advantage of the DD740 is that you can adjust the timing delay while the television show or movie is in progress. There are no disruptions to the presentation, and no set-up menus to access. You simply press the +/- buttons, and you can see the effect immediately on screen. This allows you to make adjustments on the fly easily whenever the changes in onscreen material demand it.

Felston DD740 Rear Panel

Four Audio Inputs

The DD740 has four digital audio inputs-two optical Toslink, and two coaxial. So you can connect up to four video sources simultaneously, routing all of the audio signals through this one device. Furthermore, you can preset each of the four inputs to default to the delay of your choice. For example, we put the Sony Playstation 3 into one input and found the 100 ms automatic default was perfect for the projector we were using. Then we hooked a Denon DVD player into a separate input, and found that 140 ms was needed to get the Denon's audio output in synch with the same projector.

Sometimes the synch problems will vary even from a given source. A satellite HD receiver will often deliver audio from different channels at different rates. You might find that Discovery channel looks fine with no obvious latency delays, but then you switch to HDNet, and suddenly the sound is out of synch.

Felston DD740 Remote

There is nothing consistent about these delays on satellite and cable services, and they have as much to do with the vagaries of broadcasting than the inherent delays in your own video system. But if you land on a channel that you want to watch for a while, it is a snap to use the DD740's remote to adjust the audio delay to bring everything into synch. And if you don't want to manually adjust it with the +/- buttons, you can preset up to nine different delays on each of the four inputs.


You might not have ever noticed that the video in your home theater trails the audio by just a bit. But the subliminal impact can be there nevertheless, making the movie less "real" and believable. And after reading this, you will probably look for it and become quite conscious of it in a way that you never were before. It is definitely something you will want to eliminate if you want optimal immersion in your home theater experience.

We have been particularly impressed with the simplicity, the effectiveness, and the introductory $199 price of the Felston DD740 Audio Delay (it will go to $249 when the introductory offer expires). If you are bothered by lip synch problems in your home theater, check it out. It's a solution that will bring a smile to your face.