24-bit output

You sure?

I thought I read a post from wesk05 on the Kodi forum, that all AMlogic devices are limited to 16bit audio when not bitstreamed :disappointed_relieved:

Although that would still be alot better then the static we get now :+1:

The Vero 4K is not limited to 16bit, but supports all HDMI compliant LPCM formats. :wink:

Don’t want to come over as sarcastic, but is there any proof?

Haven’t seen any comments from Sam claiming otherwise on the Kodi forum: OSMC announced new Vero4k, opinions?

It doesn’t really matter, since a very “quiet” room (or headphones) has about a 30dB noise floor, so you don’t really get much useful from the extra 8 bits, even assuming that the audio actually uses the full dynamic range available to the format. More typical rooms have a 50dB noise floor, making the extra 8 bits completely useless, since anything encoded by the lower 8 bits will be below the room noise floor.

To make the full dynamic range from 24 bits audible even with headphones would require peaks of 178dB, which will likely rupture your eardrums even with only a few seconds of exposure (it’s about the same noise level as a flash-bang grenade).

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HD audio passthrough formats require the full bandwidth that is equal to 24bit 192kHz 7.1 LPCM. Why would it therefore not support up to 24bit 192kHz 7.1 LPCM via HDMI?

It seems that bitstream supports the full range, but lpcm is limited to 16bit it seems from what I understand from the post wesk05 made in the topic I linked.
This would be a limitation to all current AMlogic chipsets.

8 channels of 192KHz, 24-bit is 37Mbps. The max bit rate for TrueHD/Atmos is 18Mbps, and DTS:X is 24Mbps. So, technically, a link could support all HD audio formats and still not support that high of LPCM.

But, if a link can support HD audio, it can support 8 channels at 48KHz, 24-bit, since that’s only 9Mbps.

IEC 61937 non-linear PCM encoded audio bitstream (aka compressed audio) is transmitted as 16-bit in IEC 60958 frame.

All Amlogic SoCs that I have checked are limited to 16-bit output for LPCM.

Have you checked the same you’ve described on the Kodi forum (recording and comparing the 24bit raw audio signal and the actual HDMI ouput) with the Vero’s output as well?

We’ve diverted from AMLogic audio drivers quite a bit (especially to accomodate most possible LPCM output formats) and it would be interesting to know whether this diversion might give a different output than other AML devices (especially concerning 24bit/16bit)…

Yes, I have looked at Vero 4K, but can’t remember when exactly. I will check again sometime soon.

This DTS HRA issue has to do with the AEBitstreamPacker used by Kodi, VLC, FFmpeg etc. Amlogic also has other IEC 61937 bitstream related issues. Frequently, it drops the Pc bits in the IEC 61937 burst preamble. This can be a problem on the lower end AVRs that rely on this information for decoding.

What evidence do you have for this? IIRC it’s kodi that constructs the IEC 61937 preamble, not the AML drivers. I’m away from home atm so can’t check. I may be wrong.

Check it on a HDMI analyzer that reports on IEC 61937 burst preamble. This was brought to the attention of Minix when they released U9H. Minix contacted Kodi developer (fritsch). Fritsch was of the opinion that it was a Amlogic problem and not Kodi problem. The issue is not reproducible on nVIDIA Shield or on Intel LE system. I have seen this on both S905X and S912. It mostlys happens with HBR bitstreams.


Sorry for slow replies, we have a lot going on at OSMC.

It’s been some time since I looked at this, but I know that we fixed some things here. I would appreciate if you can test again. I’ll also analyse the HDMITX side when I get a bit of free time.

Do you also believe this causes HRA issues as well? I don’t think this is the case myself based on some preliminary testing and some liaising with some more cooperative vendors. The last time I spoke to Peter (fritsch), I believe a consensus was reached that some AVRs are simply shitty.

If there’s an issue that you can help us reproduce, we can definitely take a stab at fixing it.


After a couple of weeks away, I’ve started to look at this. I can play a 32-bit WAV made from a 24-bit flac (so 8 LSBs zeroed) with aplay through S/PDIF, capture it, and the capture is bit-perfect. So the S905X spdif device is working as expected.

Playing the same file from kodi, it gets scaled but it still comes through as 24-bit.

I don’t have the equipment to do something similar with HDMI but there shouldn’t be any hardware limitations to 24-bit.


That is not what I find in my tests. It is only 16-bit via HDMI and S/PDIF. How are you capturing the SPDIF output?

What version of OSMC are you using?
Can you post a debug log via grab-logs -A or My OSMC?

It has the June update. I will see whether I can get the logs tonight.

Here are the logs:
Audio output: AML-M8AUDIO, HDMI

Audio output: AML-M8AUDIO Analog, PCM

HDMI output is only 16-bit in both the cases. I only tested in Kodi.

With Analog, PCM output, I do see in the log that the output is PCM32. The audio analyzer that I was using today only supports up to 24-bit 192kHz on S/PDIF input. For whatever reason, the analyzer detected no signal and I couldn’t verify what the actual bit depth was. Will have to recheck on a R&S UPV analyzer. It did play on my Denon AVR.

I had only looked at AML-M8AUDIO, HDMI output before.

I have a USB soundcard with Toslink input. It has to be set manually to the appropriate bitrate and bit-depth. It is possible that the vero is sending all 24 bits but signalling 16-bit in the metadata.

Kodi converts audio internally to 32-bit float. If that is not supported directly by the sound sink, it will try other formats with decreasing bitrate/depth until it finds one the sink supports. The SoC supports 32-bitLE. So from then on in the drivers, the signal is treated as 32-bit.

It would be interesting to try sending a 24-bit signal direct to the SoC, eg with aplay to see what comes out.

UPDATE: The way things are at the moment, if I set the Kodi audio output to PCM, I get 24 bits sent to S/PDIF for both stereo and multi-channel (FL/FR only, of course). If I set output to HDMI, I get 16 bits for stereo, 24 bits for multi-channel on S/PDIF.

If someone (like @wesk05) has the time and equipment, I would love to know what comes through on HDMI for these four conditions.

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