Digital and Analog Audio Lip-Sync Correction

DD540 Analog and Digital Set-Up

Felston digital audio delays can be used to delay stereo analog outputs such as VCR audio by placing an "analog to digital converter" (A/D Converter or ADC) between the analog stereo source and one of the DD740's inputs. You simply connect your right and left stereo audio outputs (red and white RCA connectors) to the A/D Converter where they are transformed into a digital (S/PDIF) audio signal for input to the DD740. The converters usually have both optical and coax digital outputs.

Click HERE to see one we made a special purchase on and offer for $29.95.

Even if you add an ADC to the DD740's input you "still need" a digital audio connection for the DD740's output.  It can be an A/V receiver which will accept s/pdif "digital audio" (if it says Dolby Digital or DTS it usually will) or an amplified speaker system with s/pdif input like the Logitech Z5450 and Z5500.  Many of the new low cost sound bars have optical inputs suitable for direct connection to the DD740's output without a D/A Converter. If you require analog stereo for input to your TV or audio system you will need a "digital to analog converter" ( D/A Converter or DAC) on the DD740's output to transform the signal back to analog stereo.

There are some small LCD displays that accept digital audio input and they should also work fine without a converter but that is very rare on larger flat screen TV's. Be sure your display has a digital audio input if you are planning to use your TV's internal speakers.  Don't confuse the digital audio "output" connector most new TV's have with an input. It is there to supply audio from the TV's internal tuner to an external speaker system and can't be used for input to the TV's speakers. But it can take the TV sound output to a DD740 input for lip-sync correction before it goes on to your A/V receiver or digital speaker system. In that case the TV's internal speaker volume would be set to zero and the external speakers would always supply the sound giving you the same lip-sync control over the TV tuner source as you have over the other sources coming through the DD740.

Click HERE for some suitable external speaker systems and sound bars. (We don't sell them but clicking on the pictures will take you to Amazon for current prices.)

Dolby Digital® , DTS®  and Toslink® are registered trademarks of Dolby Laboratories, Inc., DTS, and Toshiba respectively.

Fixed Analog Audio Delay Lip-Sync Correction

The DD740 is designed to provide dynamic adjustment of digital audio delay via easy remote control without disturbing the image your are watching to achieve perfect lip-sync in home theater systems. For that application we don't believe there is a more cost effective solution.

However, there are some applications where a fixed analog delay is all that's needed and most of the DD740's features would be wasted. An example might be a school or church's A/V system which produces analog audio from its video cameras and distributes it throughout the campus. Whatever video delay the system produces should be fixed and not changing from day to day like broadcasts and DVD's do.

Once that fixed video delay is determined a fixed audio delay can cancel it and restore lip-sync. Again, that isn't true in broadcasts or even DVD's which change from program to program but for the same equipment operated the same way ( no different video processing) every day it should be fixed.

While an ADC and a DAC could be added to the DD740's input and output to correct lip-sync in such a system those converters add at least $100 to the DD740's $249 cost making the solution cost over $350.  That's overkill for a fixed analog audio delay application -  especially if it is a mono and not stereo application.


A solution we often recommended for fixed analog delay requirements was the Behringer dSP110 shown on the left. It has been replaced by their FBQ100 model recently and is sold as a feedback reducer but includes an excellent analog audio delay which can be used alone if its other functions (filters,pre-amplifier, etc) aren't needed.  It has push button adjustable audio delay of up to 2.5 seconds but no remote control so it is not suitable for applications in which the video delay and hence lip-sync error varies or needs to be adjusted frequently while watching.

It has both XLR and 1/4" phono jack analog audio input and outputs and Behringer offers a rack mount that will hold four of them.  It is a mono device so if the application is for stereo audio two will be required but at less than $100 each this can be  little lower cost solution in cases where a fixed delay is suitable and all the features of the DD740 are not needed. We don't sell them but clicking the link on the left will take you to which sometimes has them.  If not do a Google search for Behringer DSP110 or FBQ100 and you are sure to find several resellers.