Please expand the areas below for frequently asked questions and their answers, plus some general information on the causes of poor AV sync.

 

Measurement Questions

Q. What type of display does Sync-One2 work with?

Sync-One2 will work with any type of display, be that a TV (LED, Plasma) or projection (front or rear) and at any resolution.  When being used with a front projector in a bright environment it may be necessary to put Sync-One2 into the projector beam.  When using a projector Sync-One2 is the only real way to ensure the video is in sync with the audio.

Q. You mention self-calibration, what does that mean?

When you first turn turn on Sync-One2, or when going back into measurement mode from the menus, it will perform a calibration.  This only takes a few seconds and is used to make things easier.  The unit determines the ambient light level which and can also normally remove any flicker from lighting from interfering with the readings.  On the audio side the gain of the microphone is adjusted, to reduce the ambient noise to a level that does not interfere with the readings.  This is why it’s important to have the unit in the measurement position when turning on or going back into measurement mode.

In addition to the calibration, both the light and audio sensors have adjustable trigger levels to alter their sensitivity, by default they are the most sensitive but can be turned down as needed using the respective option within the menus if the local environment requires it.

All these details are in the full user manual, which can be downloaded from the Support page.

Q. By accurate, how accurate do you mean?

As an indication, internally Sync-One2 is very accurate.  The smallest error between the flash and a beep detectable is 0.05 milliseconds, and all internally calculations are processed internally at that resolution.   The display is rounded to the nearest millisecond or 1/100th of a frame.

Q. I think my Sync-One2 isn’t detecting signals as it should, what could be wrong?

The majority of such issues are not having Sync-One2 in the measurement position during calibration, or having a test file playing past the lead in time.  Detection will only happen if the beep and flash are louder and brighter than the levels detected during the calibration.  So if Sync-One2 calibrates when a test is playing it will helpfully calibrate out the flash and beep, so not trigger.

If you have a space with a high reverberation time, Sync-One2 it may be required to turn the audio sensitivity down to compensate.

General Audio Visual Sync Questions

Q. What causes lip-sync issues?

Modern video processing systems in TV’s and Projectors take a finite amount of time to process the incoming video data before displaying it.  This processing time can vary depending on the input port of the device, the resolution of supplied video, and the settings on the display itself.  By comparison, the Audio more or less passes straight through the processing with a tiny delay in comparison.  As video resolution and colour depth increase with HD, 4K, UHD, and HDR the processing overhead is only set to increase and make the problems worse.

If you have a single TV and use the inbuilt speakers then everything should be in sync as the TV will delay the audio automatically to correct for the video processing delay.   If, however, at any point the audio and video are separated and processed by different equipment problems can occur.  This is why the likes of AV amplifiers have an audio delay setting, to permit the user to delay the audio by the amount required to bring things back into sync.  You will also see some TV’s have an Audio delay feature connecting external speakers or sound bars.  There are also in-line audio delay units available from various suppliers simply to introduce an audio delay to bring things back into sync.

In Post Production where the audio and video are separate elements on a timeline, there is the possibility for one to slip with reference to the other.  Some codecs, hardware, and toolsets can also introduce an error, so it becomes necessary to check the final rendered output to ensure things have remained in sync.  As a minimum general system checks should be made when any component, hardware or software, is altered or updated.

Q. How ‘bad’ does it need to be for someone to notice?

People can generally start to perceive a lip-sync error when the audio leads the video by 15ms - 35ms.  Oddly if the audio lags the video this goes up to around 80ms, probably because it’s more natural to have images arrive before the sound, for example speaking to someone across a room means you see them talking before you hear them.

Trying to adjust or check any system manually is always prone to error, as it relies on the subjective view of the person doing the testing.  Everyone will perceive the sizeof the error differently, meaning that any correction made will not be a true reflection of the system performance.  Given different sources also may have differing levels of error, the sum of the errors can lead to things looking wrong.

The ideal is to have the base system setup as accurately as possible so if a source, such as a particular Blu-Ray film or streaming service, has a slight error it may well go unnoticed.

Q. Hang on, HDMI 1.3+ supports auto-lip sync, so why do I need to do anything?

There is a feature within HDMI 1.3 and above where the display can send an audio delay figure back to it’s source.  This is a generic delay, possibly one of two, depending whether the source is an interlaced signal or not.  This is an average delay coded by the display manufacturer and only covers the average processing delay of the display unit itself.  There is also a reliance that the source feeding the display actually knows what to do with this delay when it receives it.

In real terms it’s a start, but it doesn’t take into account the entire system, just the display.  In addition there have been reported issues with the feature if the HDMI Consumer Electronics Control (CEC) is also used.  You may see this described as features such like Samsung Anynet+, SimpLink from LG, Philips Easylink, BRAVIA Link and BRAVIA Sync from Sony etc.

Ins't there an App for this?

Short version

Yes there are, but that have a number of fundamental problems.

Long version...

Indeed there are apps available.  They all suffer from a number of fundamental limitations; the use of a video camera for the ‘flash’ detection, reliance on an underlying operating system, and manual snapshot detection.

Lets talk about each of these areas;

“Flash” detection

In terms of the video camera, by definition cameras operate on whole frames.  So the minimum time period between any two readings is based on the physical frame rate that the camera can sustain during the measurement period.  This is varies between 30fps to 240fps depending on the hardware.  This can mean the potential error windows, based on frame rate alone, is going to be a minimum of around 64ms to 4ms.

Underlying Operation System

As the Apps do not directly talk the hardware, the underlying OS has to process the audio and video and pass it to the app.  The OS is also doing all the other things it needs to do, such as updating your e-mail or handshaking with cell tower.  All of these things can introduce non-deterministic errors to account for.  These delays could change with an OS update, what other Apps are running on the device, or potentially a minor change to the hardware itself.  Generally some kind of average correction factor (read fudge factor) needs to be worked out for each device model and OS version combination for you to enter into the App.  This also introduces inaccuracies, as this is an average correction, not a deterministic correction but one worked out at a single point in time and published by the authors.  (You did remember to check if this has changed since the last time you set it too, especially if there has been an OS or App update?)

For example, for the Apple devices, you have 14 types of phone (4, 4S, 5C, 5S, SE, 6, 6 Plus, 6S,  6S Plus, 7, and 7 Plus, 8, 8 Plus, and X), then throw in iPads and iPods too.  Each will have their own specific inaccuracies to be accounted for.  Add in the OS version into the mix too and things get a bit more complex.  Since iOS 7 was released 57 versions of iOS have published (iOS 7 had 10 versions, iOS 8 had 11 versions, and iOS 9 had 12, iOS 10 had 11, and iOS 11 is up to 13).  Any of these updates have the potential to cause an inaccuracy needing an approximate correction to be determined and entered, which could also be device independent.  An iOS update from 7 to 8 on an iPhone 5S has been seen to alter readings by ~20ms, or around 0.5 frames, for newer Apple hardware there are warning over problems too, causing variances or ~30 ms (thats over 1 frame!) depending on which version of iPhone you have.

One reason why the supported hardware lists are restricted is because the requirement to test all these combinations, which is an ever increasing task as updates and devices come along.

Manually assisted snapshot detection

Lastly there is the issue that you have to do some work to get your measurement, you cannot just read it off the screen in real time like you can on a Sync-One2.  To use the Apps you need to film a few seconds of video, then stop and manually slide the audio along match the video frame showing the flash (potentially one of many), to give the approximate error.  This is the the error for a single beep flash, not the system as a whole.

If the system under test isn’t perfectly stable then the error provided will not be a fair representation of the system under test, just the error of the single frame of video when the film was taken.  To really measure a system a number of readings are needed to average out the fluctuations in the system under test, also using a test with a variable gap between the beep/flash tests.  That simply isn’t possible with an App.

Sync-One2 uses an analogue light sensor, so has no minimum measurement interval.  The microprocessor in a Sync-One2 is doing nothing else but trying to do the job in hand, so nothing else can get in the way of making an accurate measurement.

Sync-One2 also shows you the error in real time, in milliseconds, and frames if required.  A running average can also be shown in real time (in frames or milliseconds) so it’s easy to watch for drift over long periods (around six hours was the longest we know about, by a company testing an international Video Conference link).  Statistics of the most recent 60 readings show you how stable a system is and help with see what is really going on.

To sum up, you can use an App if you want.  However, if you want to be accurate, have a real indication of how any system is actually performing, not spend the time doing the measurements manually, forgetting to looking up and enter correction factors and so doing it all again, simply do what the professionals do and use a Sync-One2.