Felston DD740 Review (Digital Audio Delay)

[Fred H]

Our Tivo with Prime delays video by 246ms, which we find too irritating to watch. A DD740 fixed it for us. BTW, if audio lags video it might help to get the audio earlier in the chain; for example, we could get audio from the Tivo and avoid the slight (12ms) video delay that our old TV causes.

 

[hoverdonkey]

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.

Very useful to know, thank you.

 

[sarumbear]

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?

@amirm will know infinitely more than me but I think the real reason is the engineering community was caught unprepared for the huge and fast success of video streaming.

 

[dasdoing]

for movies I use VLC, that can be synched to both sides
for youtube you have this https://chrome.google.com/webstore/...ync/mknmhikmjljhpccebpnplhicmcfjkgbk?hl=pt-BR

 

[Fred H]

Could you connect one of the ASR measured DACs to the output of the DD740 and measure its analog output?

+1

 

[phoenixdogfan]

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.

JRiver does it too and has both negative and positive values.

 

[sarumbear]

@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.

If the digital signal is clear, what do you expect the DAC output to be?

 

[PeteL]

If the digital signal is clear, what do you expect the DAC output to be?

Yes it would really only be testing the performance of the DAC, but I would like too to see how well modern dacs recover 120ps of jitter. Amir states "reasonably low" but its in the grand sheme of things " Fairly high" Jitter recovery on SPDIF receivers on various DAC is still not fully equal across the board. A bit more so with Toslink. I am not fully confident that "losing one bit of information" is the only measure there is to worry about. Especially that this calculation is for 16 bits. This 120 ps is "pre" transport trough the cable and "pre" any interference on the line. It should be OK really, but it would be great to assess it trough measurments. @amirm was this jitter measurment trough Coax or Optical? Which sample rate/Bit depth? I could I guess find formulas online but when you say it needs 500 ps to obliterate one bit, is this at 44.1K? Would that suggest that this is not capable to transfer Hi-Res in a bit perfect manner?

 

[sarumbear]

Yes it would really only be testing the performance of the DAC, but I would like too to see how well modern dacs recover 120ps of jitter. Amir states "reasonably low" but its in the grand sheme of things " Fairly high" Jitter recovery on SPDIF receivers on various DAC is still not fully equal across the board. I am not fully confident that "losing one bit of information" is the only measure there is to worry about. this 120 ps is "pre" transport trough the cable and "pre" any interference on the line. It should be OK really, but it would be great to assess it trough measurments.

IMHO, that would be better done as a separate test where a DAC is fed from a generator where jitter is adjustable and the output is measured. Why would you use a delay device as a generator?

 

[PeteL]

IMHO, that would be better done as a separate test where a DAC is fed from a generator where jitter is adjustable and the output is measured. Why would you use a delay device as a generator?

Fair enough, just general curiosity on my part, I just think this subject may be a bit underexploited on this site and good info backed with measurments are hard to find. For exemple, 192 kHz transnission on Toslink, altough officially supported is still to this day a hit and miss where in many cases dropouts and stuttering are not rare. Now Toslink has the advantage of being unafected by electrical interferences but has it's own set of limitations that translates in Jitter. I agree this is a larger debate, probably for an other thread. Just saying that we have a jitter metric here that is higher than most SPDIF outputs out there, could be interesting to know if modern equipment (DAC) immunity can easily work with these caliber of performance. And if this limits the file formats that can be supported.

 

[Jim777]

Having worked in audio coding (and a *very tiny bit* in video), I'm very susceptible to being bothered by coding artefacts, but I'm pretty glad that I never trained myself to notice audio/video sync issues!

 

[Obiwan007]

yea, normaly video needs to be delayed. at least for us DSP users. needs a HDMI input to be able to realy sync

Most AVR have an option to correct the delays aka lipsync. My old Denon AVR-X4400 can do it.
With a video buffering option this would be probably way more expensive...

 

[yahrightthere]

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.

Hmmm it's maybe me, but trying to press A while a video is playing & changing the negative or positive values doesn't work for me.
Does it work or not work for anyone else?

 

[nagster]

If the digital signal is clear, what do you expect the DAC output to be?

I can't answer. I don't understand the definition of "clear" in this case.

My hypothesis is below and I'm curious about what the outcome will be.
If the output signal waveform of the AP and the output signal waveform of the DD740 are the same, there should be no difference in the measurement result of the DAC with or without the DD740.
If there is a difference between the output signal waveform of the AP and the output signal waveform of the DD740, the difference may also appear in the measurement result of the DAC.

 

[PeteL]

I hear from all the post that there are many simple solutions to correct Audio-to video lipsync issues, and as stated, most of the time audio is already late. but this device has to have other applications than that, adjusting 1/3 msec is crazy short, anything under 10 msec delay is undetectable, and that's for percussive stuff, for talk it's much more, 50msec, even more nobody can detect a delay... So that kind of precision, what for? maybe more precisely insuring that two sound source are precisely in phase, stuff like that we are more at the waveform, few samples level than correcting lipsync issues here, I am curious what the main reason people buy that. And I am just talking audio perception here, which is many time more accurate than the eyes, let's not forget, 1 video frame is 33 msec....

 

[KxDx]

Having worked in audio coding (and a *very tiny bit* in video), I'm very susceptible to being bothered by coding artefacts, but I'm pretty glad that I never trained myself to notice audio/video sync issues!

When lag is bad enough, you can't unsee it. It's not 70's Kung Fu movie bad, but your brain will keep telling you somethings not quite right. Then if you start looking too closely at mouths on the screen the insanity begins.

 

[CedarX]

When lag is bad enough, you can't unsee it. It's not 70's Kung Fu movie bad, but your brain will keep telling you somethings not quite right. Then if you start looking too closely at mouths on the screen the insanity begins.

Interesting point: I wonder how much of this is a “training” issue or a particular individual sensitivity. CC are significantly out of sync, yet I (my brain) don’t perceive this as an issue. Is it because it is purely visual?

 

[stevenswall]

I have never seen a problem this would solve.

The Audio and Video are in sync on the TV.

Audio it output and is now no longer in sync if there is any processing.

TV makers seem oblivious and allow adding delay to the audio, when they should allow adding delay to the video instead.

 

[Berwhale]

Funny that my lip sync problems were only with my LG OLED TV

You might try turning off all the image processing on your TV. Try setting it to 'gaming' mode if it has one.

 

[Timbo2]

Kodi does it too but, unlike this box, it is not very convenient, as the setting is a few layers deep.

Nvidia Shield TV has a system wide setting that will adjust delay for all the applications.