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Nvidia Shield PCM over HDMI quality

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Jun 27, 2020
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#1
In older versions of the Nvidia Shield OS, if you went to the HDMI status page, it would only list PCM 16-bit as the maximum audio mode setting. This page on Nvidia's help site still shows a picture of the setting: https://nvidia.custhelp.com/app/ans...o-is-not-working-with-certain-video-streaming . More recent builds of the OS not longer show this information or provide any audio mode settings mentioning PCM.

How I read this info back when it was visible was that the Shield outputs all PCM audio as 16-bit over HDMI. So any 24-bit content decoded to PCM, or originating as PCM, gets downsampled to 16-bit on it's way to the AVR or processor over HDMI. All PCM audio may have been resampled to 16/48 in older builders as well. The only way to keep 24-bit content as 24-bit would be to bitstream it (as TrueHD or DTS-HD MA) to the AVR or processor (bad if you have a lot of Blu-ray TrueHD and DTS-MA converted to 24-bit FLAC 5.1/7.1).

It's not clear if the audio mode options were removed at some point the because the Shield Experience OS or the underlying Android OS improved their uncompressed audio output handling, or Nvidia just wanted to hide it because it highlights a major downside of the product.

In my current tests the sample rate is kept at it's original rate. For example playing Akira's 24/192 5.1 track stored as FLAC shows as PCM 5.1 192 khz source on my Denon receiver. But I have no way to test the bit-depth.

So does any know if this is true, or how to test for it? I'd guess one way to check would be to have equipment that can check the incoming audio bitrate, 16-bit 5.1 would be 4608 kbps and 24-bit would be 6912 kbps. And it should match source's properties of course, not be all 24-bit or all 16-bit, indicating resampling. The playback software (Kodi, Plex, Emby, etc) could also be a factor complicating testing I believe.

Thanks if anyone can shed some light on this!
 
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