Frame rates

A system should be running at a consistent frame rate for optimal sync, from source to the final display.  There will be issues if there is any frame rate conversion unless the frame rate is an exact multiple of the source material.  You can often easily spot such issues with Sync-One2 as readings are shown to you in real-time. When you take measurements, there will be a repeating pattern.  Such as +75, +73, +71, +69, +67, +75, +73 etc.  which shows the errors caused by the frame rate conversion.

For example, a film playing at 23.98 frames needs a display running at 23.98 or 47.95 frames.  Content at 24 frames will be OK at 24 or 48 frames, and yes, 47.95 isn't "close enough" for there not to be an issue.  Note that many domestic displays will only show the input frame rate rounded to the nearest whole number, so content sent at 23.98 will almost certainly be indicated as 24.

So for best results, always set the source to output the frame rate of the source material, be that a Blu-Ray player or an Apple TV.

Measurement position

Whilst it may sound obvious, take measurements in the optimal viewing position or the sweet spot.  While this may not make a massive difference in the average home cinema, the mixing desks in large Post Production spaces can be a long way from the screen (17m is the longest distance we know about).

Play test files from the start where you can

The 10 second lead in our test files is to let Sync-One2 calibrate to its environment.  It also enables the playback to settle into a steady-state.  Starting and stopping the test files can introduce offsets unless the whole system is mastered to a reference clock, as in Post Production facilities.

Motion smoothing

If your display device, especially a projector, has motion smoothing then disable it whilst you set the sync.  We often get asked why the sync jumps around a lot with projectors, and it nearly always comes down to the motion smoothing getting in the way.

The only way to check a streaming service is to play a suitable test file on that service on the device you usually use.

Unfortunately, we are not permitted to publish the details directly.  So for further information on streaming services that host Sync-One2 suitable test files and how to access them, you will need to drop us an e-mail with "streaming service details" in the subject line.

Depending on the device used to access the service, you may be able to play one of our test files via a locally installed player.  Such as installing VLC on an Apple TV and playing a test file shared from a local PC.

If you subscribe to a streaming service and would like them to host suitable test files, please let them know!  We are always willing to provide as much assistance as possible to service providers.  Many of them use Sync-One2 internally already.

Q. What causes Audio Video (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 the supplied video, and the settings of 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 worsen the problems.

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 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 soundbars.  There are also in-line audio delay units available from various suppliers 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 checking the final rendered output becomes necessary 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.

This website has some great details on the causes of AV latency.

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 person's subjective view of doing the testing. In addition, everyone will perceive the size of the error differently, meaning that any correction made will not be a true reflection of the system's performance.  Different sources may also have differing error levels, so 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 its source.  This is a generic delay, possibly one of two, depending on 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 consider 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 Samsung Anynet+, SimpLink from LG, Philips Easylink, BRAVIA Link and BRAVIA Sync from Sony etc.

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

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

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

When you first turn on Sync-One2 or go back into measurement mode from the menus, it will calibrate.  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. They are the most sensitive by default 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 you can download 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 internal 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?

Most 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 and not trigger.

If you have a space with a high reverberation time, you can increase the mask time to give the sound time to decay before Sync-One2 re-arms for the next measurement.

Q. Why a V2?

The original Sync-One2 has remained essentially unchanged since 2014. However, since launch, several requests have been received for additional features, which customised bespoke versions for various customers have accommodated. These have required both firmware and hardware modifications.

Technology has also moved along since 2014, so we decided to bring Sync-One2 up to date and roll in previous custom enhancements into a new version. As a result, everyone benefits from the added features and creates something more flexible for those who need them.

Internally Sync-One2 is based on new hardware, requiring the firmware to be ported to a new processor. Improvements that were not possible before and the ability to have new features added with a firmware update not previously possible.

Q. What does v2 do that the original didn't?

Well, where to start.

The most obvious difference is the addition of two additional holes in the case on the left-hand side. These are for a 3.5mm audio input jack and a USB Mini-B connector. The audio jack is a regular stereo input (downmixed to mono internally) that enables v2 to be directly connected to a headphone or line-output interface to take an audio feed rather than use the internal microphone. The switchover is automatic but may also be overridden via a menu option if needed.

The USB Mini-B will appear as a standard Serial port on Windows, Mac, or Linux computers. Without any additional effort, v2 will log all readings taken in Measurement mode to the port, so it becomes easy to grab readings. Via this port, there is also an API interface to v2 to remote control the unit. So Sync-One2 v2 may be used as part of a bench calibration or inspection process or to quickly obtain more detailed statistics to generate a certification report for an installation you can give to a client to show them the data.

Should the unit get mislaid, you can also add a custom startup splash text to the display (via the API), such as your name and number. We can also program a permanent custom message at the time of order. Such as a company ownership message, or branding, in a way that a user cannot remove, like a label or asset tag.

The USB Mini-B port also permits the end-user to upgrade the firmware when new features come along or require some new function or feature not currently there.

There are also new features, such as adjustable Mask Time for spaces with long reverberation times. Enhanced sensitivity of the light and audio detection sensors. Brighter display, which is also now blue rather than white.

Q. What is a feature or support code?

A Support Code is an easy way to pass information about any given unit back to us for support. The code contains unit-specific information such as serial number, firmware revision, and installed or activated features. It may also be requested to verify ownership for specific requests for complex test files.

A feature code can perform a specific action specific to a Sync-One2 v2, enabling an enhanced feature for example.

Q. What about support for my original version?

There is still support for the original version, and the warranties remain valid. In addition, should a unit require service, we have spares if there is a problem or a unit suffers physical damage.

I press the On button, and nothing happens.

For Sync-One2 v2, you must hold down the On button for a few seconds to turn the unit on.  Why may you ask?  Well, Sync-One2 does turn on when you press the button, but it is very busy performing internal verification checks.  Once these are complete, the display will wake up, and everything is ready to go.

What does "Waiting for PC" mean on the display?

During power-up, Sync-One2 verifies the internal firmware is intact and has not been tampered with.  If this fails for any reason, then this message is displayed.  It means the unit is awaiting firmware to be uploaded, which can be downloaded via the support pages.

Normally this error only happens if a firmware upgrade has been interrupted, so try again.  However, if an attempt has been made to tinker with the firmware, please stop it and reload the unaltered firmware.

If the error appears at first power on, and then Sync-One2 starts up as normal after around 30 seconds, buy a lottery ticket.  The probability of a Sync-One2 doing this is 1 in 4,294,967,296.  If this keeps happening on your Sync-One2, please get in touch, it is easily fixable, but we will need the unit back to work some magic.

Short version

Yes, there is, but it has fundamental problems.

Long version

Indeed there is a 'One and only Sync Checking app' available. However, it suffers from many fundamental limitations: using a video camera for the 'flash' detection, reliance on an underlying operating system, and manual snapshot detection.

Why is there only one? Probably as you need to do all the work, you don't get an accurate view of the system under test and have bought a costly handset to use it.

Let us talk about each of these areas;

"Flash" detection

By definition, video cameras operate on only whole frames. So the minimum time between any two readings is based on the physical frame rate that the camera can sustain during the measurement period. Frame rates vary between 30fps to 240fps, depending on the hardware. So based on the frame rate alone, the potential accuracy is limited before starting.

Underlying Operating System

Apps do not directly talk to the hardware. Instead, the underlying OS has to process the audio and video and pass it to the App. Of course, the OS is also doing all the other things it needs to do, such as updating the display, checking your e-mail or handshaking with a cell tower.

Modern handsets process the video and audio they capture. They are, after all, trying to give the best image and sound they can.  Some of this processing happens in the firmware inside dedicated hardware, and some in the operating system.

All of these things can introduce non-deterministic errors.  So for every handset model and OS combination, you must determine a fudge (or correction) factor to offset the errors introduced by taking the measurements.  The App provider may provide this correction factor, or you have to do that before you can take measurements.

Manually assisted snapshot detection

Or, more simply put, you have to do all the work.  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 video of the system under test, stop and manually align the video to the flash and lock it, then scrub the audio along to align it to the video frame showing the flash.  Once you've done that, you have obtained a single approximate measurement, which isn't an accurate view of the system, just the one reading.  To get a precise picture of the performance of a system, you need to take many readings and then calculate the statistics.

Summary

To sum up, you can use an App if you want. However, if you're going to be accurate, have a real indication of how any system is performing, and not spend the time doing the measurements manually, do what the professionals do and use a Sync-One2.

PS. Don't forget to look up or obtain the correction factor and have to do it all over again.

Please note that some playback solutions may show an audio latency of 2112 samples because of the nature of AAC encoding.  This is equal to an audio delay of 44ms for 48 kHz audio (this translates to an audio stream that can be late by around 1 frame in 24/25 fps and around 2 frames in 50/60fps ).  While some decoders compensate for this latency, not all solutions do. Therefore, it is recommended to use the PCM files to measure the latency of your system with the best possible accuracy.

To check your system's audio/video synchronization, make sure to check with either PCM or AAC files depending on the audio format you use primarily on the system to calibrate.

You can read more about this delay caused by AAC encodings here: https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFAppenG/QTFFAppenG.html

Credit to DXOMARK for some in-depth technical analysis to identify this issue.