Hector Martin on Twitter: "I have a suspicion as to what causes this and Linux might already have a quirk to deal with it. I think this happens when the USB transfer size is not a multiple of the number of channels."

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Hector Martin‏ @marcan42 9 Jun 2020

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And yes it eats up HDCP streams no problem.

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Hector Martin‏ @marcan42 9 Jun 2020

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Looks like you don't get all 1920 pixels horizontally, though. It seems to be more like half the horizontal res, due to some kind of filtering. You do get 1080 lines though. So 960x1080 effectively? First image is the cheap thing, second is an AverMedia LGP2 (crop of 1080p frame)pic.twitter.com/kwANLY2wWZ

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Hector Martin‏ @marcan42 9 Jun 2020

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At 1280x720 you do get all the pixels you paid for, though, but there is some kind of horizontal sharpening being applied. Again, compared against the LGP2.pic.twitter.com/NREwPMiR0o

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Hector Martin‏ @marcan42 9 Jun 2020

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(Right click and open those images at original resolution to get the proper idea; Twitter always scales by default)

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Hector Martin‏ @marcan42 9 Jun 2020

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I would rate the artifacts at 720p as a bit worse than the LGP2, but not terrible (chinese left, LGP2 right). This is after adjusting the brightness/contrast/saturation/hue on both to attempt to match the original image (neither has good defaults).pic.twitter.com/sVYN4OVp5t

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Hector Martin‏ @marcan42 9 Jun 2020

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So I would call this a fairly capable 720p capture card overall, and only slightly lower performance at that resolution than devices that cost 10 times as much. At 1080p things are a bit messier, but it does work.

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Hector Martin‏ @marcan42 18 Jun 2020

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So it turns out they report audio at 1ch 96kHz, but it's actually 2ch 48kHz. Currently testing a quirk patch for Linux, assuming it works as intended expect it in a stable series near you once it percolates through the pipeline.

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Hector Martin‏ @marcan42 18 Jun 2020

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FWIW, interpreting 48k stereo as 96k mono (and downsampling to 48k, because you are, right?) is mathematically equivalent to a clean mono mixdown except one channel is delayed by 0.5 samples, which is negligible. So it's safe to use the card on Win/Mac and pretend it's mono.

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Hector Martin‏ @marcan42 18 Jun 2020

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Basically for mono (center panned) content you'll get a slight high frequency rolloff (4dB or so at Nyquist = 24kHz), and hard panned content will sound fine with no distortion.

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Hector Martin‏ @marcan42 18 Jun 2020

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OMG. I think this is why they claim 96kHz mono. Assuming this isn't a bug in my USB config... these things have a hardware bug which briefly swaps the channels intermittently. Every second or so. So they probably set it to 96k mono as a hack so you won't notice!pic.twitter.com/XGnJ9OQogJ

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Hector Martin‏ @marcan42 18 Jun 2020

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I have a suspicion as to what causes this and Linux might already have a quirk to deal with it. I think this happens when the USB transfer size is not a multiple of the number of channels.

8:09 PM - 18 Jun 2020