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Felston DD740 Review (Digital Audio Delay)

amirm

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This is a review and detailed measurements of the Felston DD740 Digital Audio Delay/ Lipsync Correction and input switcher. It was sent to me by the company and costs US $249.
Felston DD740 Review Audio Delay AV Home Theater Lip Sync.jpg

As you can see, the DD740 is a compact device. The main controls are input selection and changing of the delay in milliseconds (or optionally 1/3 msec). Up to 9 settings can be stored for each Toslink optical or Coax input and recalled using the remote:
Felston DD740 Review Remote control Audio Delay AV Home Theater Lip Sync.jpg



I like the super responsive change of the delay.

Felston DD740 Measurements
The first thing I measured was the accuracy of the delay and it was right on the money. This is an example of setting the front panel to 50:

Felston DD740 Measurements Audio Delay AV Home Theater Lip Sync.png


As you see, it is accurate to two decimal places.

The only other test I could think of was jitter:
Felston DD740 Measurements Jitter Audio Delay AV Home Theater Lip Sync.png


Jitter is of course worse than the Audio Precision APx555 analyzer but peak is about 120 psec which is reasonably low. As a comparison, you need 500 psec of jitter to obliterate one bit of 16 bit audio. Given audio sync issues, I will take some jitter every day of the week and twice on Sunday! :)

Conclusions
As a person who has worked in broadcast video industry and gotten grilled and beat for incredibly small amount of audio/video sync issues, I am hugely bothered by the poor sync between audio and video in broadcast, streaming and stored content. Not only each source is different, but also from program to program! Audio is slaved to video and getting the two in sync is more of an art and science at times and naturally, many encoders (offline or online) get it wrong. It is so annoying to set the delay on one channel of cable TV, change channel and have it be out of sync again! With DD740 you can make corrections on the fly using the remote. To the extent the delay differential is channel/source specific, you can put it in memory. Or make quick fine refinements as needed.

I am happy to see a standalone product at reasonable cost solve this issue as the industry syncs into worse and worse problem in this domain.

I can recommend the Felston DD740 for its unique functionality.
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EJ3

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I have noticed the issue from time to time but for the issue to be bothersome to me it needs to be an extreme case of it. That being said, for those that the issue bothers more than me, this seems to be a great solution at a very reasonable price. In fact, the price is so low that I could see getting it just to have the ability that it provides on hand.
 

TheBatsEar

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Nifty device and should help a lot of folk.
Sadly, in my case, video runs ahead of audio.:facepalm:

I suppose this device doesn't allow negative values for the delay?
 

sseppala

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Just thinking, this could be a lot more useful if it could also act as a digital volume control. It would be easy for a simple PCM input, but re-coding Dolby Digital and DTS would be more challenging.
 

sarumbear

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Content with inconsistent/incorrect syncing is a major issue. However, I can't think how this device will be useful. Even the same movie can have different delay values throughout.

Find a delay that's a good compromise for most content and try really hard not to focus on it.
 

nagster

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@amirm Thank you very much.

Could you connect one of the ASR measured DACs to the output of the DD740 and measure its analog output?
I would like a dashboard, IMD sweep, multitone, J-test.
I am interested in the difference with and without DD740.
 

Dennis_FL

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I went through 3 sound bars with lip sync issues (2 Martin Logan, 1 Sonos) . The worst was the first generation Sonos with Toslink. The second generation Sonos with eARC HDMI has it solved. Never a problem. Also no problem with an AVR receiver with eARC. Funny that my lip sync problems were only with my LG OLED TV. I have a guest bedroom TV with a sounder that has perfect lip sync.

And I get Atmos now.
 

vkvedam

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Very useful to conduct A/B tests without messing around with the source :)
 

KxDx

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My Marantz NR1200 needs a 125ms delay for my Roku. It's more noticeable on Prime and HBOmax than it is on Netflix for some reason, but 125ms seems to be the "one size fits all" setting for that receiver.
 

PeteL

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Content with inconsistent/incorrect syncing is a major issue. However, I can't think how this device will be useful. Even the same movie can have different delay values throughout.

Find a delay that's a good compromise for most content and try really hard not to focus on it.
Maybe, but wow. What does it say about the state of technology? I am really curious about this statement, in 2022 that the A and the V cannot stay in sync for the duration of an hour and a half movie, not only not in sync but with delay value fluctuating so much that we need to settle for a for a middle approximate value and accept it? What's going on here... I don't disagree with your statement and I have also notices that this issue do exist, I don't always notice... But I find that totally unacceptable in this day and age. What's going on here? And what's the real solution, beside going for such a basic approximation?
 

MarcosCh

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My tv costed not much more than this device 4 years ago and has adjustable sound delay... but as always, there are as many use cases as users.
 
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julian_hughes

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Kodi does it too but, unlike this box, it is not very convenient, as the setting is a few layers deep.
Audio sync is available as keyboard shortcut. Just press A while video is playing and you can change the audio delay on the fly with negative or positive values, so no need for a separate video delay.
 
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