Originally Posted by KC-Technerd
I'm attempting to use the A/V Sync pattern to attempt to set an audio delay on my new A/V receiver. My new receiver is apparently much faster than my old one as the audio is very apparently ahead of the video now, where it did not used to be. The receiver has a delay setting in 5ms increments. I'm trying to adjust this by the recommendations in the Pattern Help Text, but even when blocking out everything except the individual numbers, the longer I look at it the less certain I become about whether the flash is before, during, or after the beep.
Yes, this can definitely be a problem. I find it easier with the "block out everything but a single number" approach, but not everyone seems to find it useful. It can also be illuminating to deliberately set your delay way too high and way too low so you have a feel for what too soon and too late look like. One line of thinking is that if you really can't tell if the sound is ahead or behind, it's probably close to correct.
Googling this I found that there is some very expensive equipment available (SynCheck) to aid in adjusting AV sync, and I found an iPhone App called "Catchin' Sync" for $13.99. Anyone have any experience with that App, or any other suggestions on a way I can get a more objective and accurate synchronization?
We designed our sync checking pattern to work with audio sync checking hardware, so it should work well with the SynCheck device. There are other tools, but I don't know if any of them are any cheaper than the SynCheck. Some people check sync with a scope, by feeding the video and audio signals in and watching for the matching spikes. This gets hard with HDMI, since you need an HDMI analyzer that can display a specific scan line and the audio on the same scope trace, or have a dedicated audio/video sync test. There are several fancy waveform monitors from Tektronix and others that will do this, but they're incredibly expensive pro gear. The other problem is that you're measuring the delay at the input to the display, but are not measuring the delay introduced by the delay itself. For that reason, it's generally better to either use your ears/eyes or use a photodiode pointed at the top of the screen and a microphone sitting in your viewing location.
If you had a decent two-channel oscilloscope just lying around, you could wire in a microphone and a photocell and you'd be cooking with gas. There are older analog oscilloscopes selling for less than $100 on eBay, but you'd need to be reasonably handy with electronics to get it working. I would bet someone could make an arduino project for sync checking for less than $100. Check out this page about reading a photocell and reading sound levels via arduino for more:
The iOS app seems reasonable in theory, but I really don't know how good the sync is between audio and video capture on the iPhone. I certainly can't see any way you could get the sync closer than 1 frame period of whatever the video capture rate on the iPhone is. If the capture rate is 30 fps, that's not good enough. If it's 60 fps and the audio sync is very good, you could perhaps get reasonably close. The SynCheck folks tested an iPhone and found it lacking, but they're hardly unbiased. Still, I'd read their analysis just as a counter-argument.