Here is a review of the DD340 that a customer posted at the home theater discussion group www.avforums.com. With his kind permission, we reproduce the review here in its entirety, word for word.
"OVERVIEW & CONNECTIONS:
The Felston DD340 is a digital delay unit that works in the digital domain. It has one coaxial SPDIF input and one coaxial SPDIF output. Whilst it does not directly support TOSLINK, you can put interim media convertors in place easily obtainable from the likes of Maplin or Lektropacks. Just a little larger than your hand it takes up very little physical space. The only other connection on the back panel is for external DC power.
It will accept most common digital audio formats, including Dolby Digital, DTS, PCM - all up to 96/24 and delay them up to 340ms (170ms for 96kHz content). You can connect your DVD player, Sky+, Freeview - anything with a digital output.
What is nice about this unit, is that it comes with a remote control so you can adjust the delay from your armchair. The green 3 digit LED display is bright enough to be readable during daylight hours but not so bright as to be obtrusive during an evenings movie watching. It clearly shows you the current delay time and briefly shows which preset you have just selected. You can store up to 6 preset delays, which are easily done with the simple 6 button remote control.
The remote allows you to increase or decrease the delay in 1ms steps. You can also change the preset number and store delays and turn the power on and off. This should probably be thought of as a bypass function, rather than power. In standby (and also when completely powered down ie. no DC power at all), the unit goes into bypass mode which means it does not apply any delay at all and passes the digital stream as if it wasn't there.
As a home user, I cannot comment on jitter levels or other such technical details. I shall leave that for someone more experienced. One thing I really like about the DD340, is that when setting delays it applies them after a short pause. Many AV amps will apply the new delay straight away resulting in glitches as the user adjusts the delay time. The Felston waits about half a second after the user has stopped changing the delay before applying it. This results in a brief pause of the audio stream before resuming data flow. It's a small point, but applying the new delay in this way shows how much thought has gone into the design.
With a 60ms delay (my Meridian 561 can only manage 30ms), lip sync on most DVDs is solved. If it isn't, I can just remotely increase or decrease it. Be it Dolby Digital, DTS or just ProLogic, I can now watch and enjoy the film rather than getting irritated by the lips moving after the audio is presented.
For under £200, this is clearly a cheaper solution than the Vigatec offering. For all plasma/projector owners who have forked out a princely sum on their large screen systems but do not have a delay facility on their prized audio system, the Felston DD340 is surely a must."
- Chris G, UK