Raspberry Pi 4 can finally boot directly from USB

Re:Raspberry Pi 4 can finally boot directly from USB by loxias on Saturday September 19, 2020 @12:34PM (#24528616)

I beg to differ: a good rule of thumb is that an (audio) sample takes about 8mm (44.1k). By the time you're a full 1ms late, that's a 44 sample difference between the two (or that's as though the speakers were about a third a meter apart.

And that distance, you're gonna hear some uncomfortable comb filtering. A third of a meter corresponds to a frequency of about 1khz, which is right smack dab in the middle of a critical band, so you WILL hear the constructive and destructive interference around ~1khz.

(and _5ms_? That means the speakers are now ~220 samples out of sync, so I'd expect any lows around 200hz to have some destructive interference, making the music sound hollow.)

1ms of sync is FAR less than adequate. It took effort, but I was able to get a distributed set of raspis to within about 5 samples at 44.1k, and I think I can do better.

Why do I know this or care? :) I've done (and still do) a lot of research (and inventions) in the field of microphone array processing and audio source localization -- tracking objects purely by their sound. With cheap commodity equipment I can generally get a resolution of 5cm, and with lots of fine tuning I was able to do sub-cm tracking.

[ Parent | on HN ]

Re:Raspberry Pi 4 can finally boot directly from USB by Dylan16807 on Saturday September 19, 2020 @02:48PM (#24529614)

All those problems happen even if your speakers are perfectly in sync. These aren't headphones. If you have a couch for listening, the difference between sitting on the left and sitting on the right is just as big or bigger. You get the same interference, yet it isn't a problem.

[ Parent | on HN ]

Re:Raspberry Pi 4 can finally boot directly from USB by m463 on Saturday September 19, 2020 @04:53PM (#24530252)

I think his thinking is still valid.

If you sit on the left or right the sound should still come from "center stage" or (x,y,z)=(0,0,0) without being shifted or drift.

[ Parent | on HN ]

Re:Raspberry Pi 4 can finally boot directly from USB by Dylan16807 on Saturday September 19, 2020 @05:40PM (#24530490)

Depends on whether you have a stage. If you're playing audio to go with a TV you don't want it drifting much. But when the scenario is playing music over an area you end up with a bunch of mutually-contradictory centers and it doesn't matter if they shift over a little. And music over an area is what sparked this talk.

[ Parent | on HN ]