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Comment by lsmarigo | Hacker News Reader

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lsmarigo·

minor gripe the apt-x website under "Key Facts"

"Your brain can’t tell the difference between a delay of 0 and 100ms"*

Reminds me of the old "brain can't process more than 30fps" Marketing folks running wild over there.

* https://www.aptx.com/aptx-low-latency*

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It's flat untrue, too. You can hear audio latency nearly down to single-digit milliseconds. In fact, there's a fun recording trick where you duplicate a track, pan it hard left and the original hard right, and then delay one by 10ms. (They get heard as two separate parts even though they're completely identical.)

The most common thing is video-audio sync, and regular user would barely recognize 40-60 ms delay between video and audio track.

Yeah that's probably fine. Humans have some sync tolerance because speed of sound is so low. Something 15m away will have 44ms delay of the sound compared to the vision.

But there are other areas where tolerance matters more I think. Say you press a key and sound comes either after 5ms or after 50 ms. I think that would be noticeably different.

Interestingly, I use Bluetooth headphones with my TV and I have never noticed issues with audio/video sync. Have modern Bluetooth stacks reduced the problem or is the TV compensating for the latency by delaying the video?

"100ms" probably comes from the long distance telephony investigations into round-trip time. If I remember correctly, 100-ish ms RTT was when people would start to notice the delay, and conversations became very difficult above ~200 ms. As a result, a lot of telephony hardware tries to keep latencies under that limit.

The brain obviously notices far smaller latencies.

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