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Author Topic: SCREECH when switching between PCM & Bitstreaming Atmos  (Read 1066 times)

murray

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SCREECH when switching between PCM & Bitstreaming Atmos
« on: March 10, 2023, 05:38:33 pm »

Sorry folks but I have asked this before but still never got to the bottom of the problem. All I remember was it wasnt due to JR but maybe someone good on audio might be able to help me....

I have a McIntosh MX160 with two of their 7 channel amps. I use a HTPC with JRiver. I have a 7.1.4 Atmos setup.

My problem is, I cant use bitstreaming as whenever the mkv files on my Nas change from any HD audio and back to pcm I get a horrible scream through the sound system.
Which means I donít get my Atmos speakers firing as I have to use PCM. On PCM everything is perfect, as soon as I switch back to bitstreaming in JRiver I go back to the horrible screech when a file changes from PCM to HD audio.

Ive put up with this for years and years and donít know who to turn to. Can someone please help me please as Ive tried everything possible. There are no settings in JRiver that Ive found to prevent this that Ive tested. Delay at startup etc etcÖ

I want to run in bitreaming so get the full effect of my Atmos setup.

What can I try or test please to stop this, SCREECH?

I hope someone can help me!
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jmone

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #1 on: March 10, 2023, 06:05:45 pm »

Hi Murray,

It sounds like the MX160 is not changing from PCM to bitstreaming (and you are hearing the raw undecoded bitstream). 

I just tested with Bitstreaming on then played two separate clips, one with HD Audio (that bitstreaming) and one without (and it was decoded).  I tried in both orders.  No issues. 

Couple of things:
- I take it these are multiple separate files (not one merged file)?
- Is there anything between the HTPC and the MX160 like a HDMI/DVI Doctor etc that could be keeping it in PCM mode?
- It may be worth trying the latest version of MC as there was an update to LAV Audio that fixed some bitsreaming issues for me (but that was on an Intel NUC).

Thanks
Nathan
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murray

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #2 on: March 10, 2023, 06:36:34 pm »

Hi Nathan, thanks for the reply.
Im using a mix of files from a playlist, some just pcm 2 channel (trailers) then a feature in HD audio, maybe sometimes Atmos.
The MX160 does switch from PCM to bitstream between files as its verified on the front pannel of the MX160, however I get the screech between every single file for 2 secs. Its so loud I just have never been able to run in bitstream for years, so my Atmos is unusable.

MC set to Bitstream
pcm file to pcm file = screech
pcm file to HD audio file = screech

MC set to PCM (recommended but no Atmos)
pcm file to pcm file = NO screech
pcm file to HD audio file = NO screech
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jmone

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #3 on: March 10, 2023, 06:56:29 pm »

So to be clear, when MC is set to Bitstream it screeches for 2 seconds between tracks but then it is fine?

The things I would try would be:
- Upgrade to the latest version of MC (to see if the HDMI Bitstream change makes any difference)
- MC  Options --> Audio --> Audio Device --> Device Settings --> Toggle "Disable event style"
- MC  Options --> Audio --> Settings --> Play silence at startup for hardware synchronization (try say 10 sec then work backwards)
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murray

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #4 on: March 10, 2023, 07:17:09 pm »

So to be clear, when MC is set to Bitstream it screeches for 2 seconds between tracks but then it is fine?

The things I would try would be:
- Upgrade to the latest version of MC (to see if the HDMI Bitstream change makes any difference)
- MC  Options --> Audio --> Audio Device --> Device Settings --> Toggle "Disable event style"
- MC  Options --> Audio --> Settings --> Play silence at startup for hardware synchronization (try say 10 sec then work backwards)

Just updated to the latest version of MC and still have the screech between files. (Not sure if you have to restart PC after an update?)
"Disable event style" doesnt fix the screech between files.
Play silence doesnt fix screech, tried all the way up to 20 secs.
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jmone

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #5 on: March 10, 2023, 07:30:15 pm »

Another thought, are the clips all the same or different FPS?  as there can be audio issue when changing frame rates as the HDMI link can be reset for a short period.  If so you could also try Options--> Video--> Display Settings --> Wait after change (try 2 sec).

Also I'm not sure about how "Play silence at start for hardware sync" ment to work, as I just tried it and did not really notice any "silence" regardless of the setting (well maybe a sub second difference even when set to 45 Sec).
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jmone

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #6 on: March 10, 2023, 07:33:06 pm »

If that does not work then Turn On logging (Help --> Logging) play the offending clips, stop playback, post the Log here, then turn off logging again.
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murray

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #7 on: March 10, 2023, 07:34:12 pm »

Another thought, are the clips all the same or different FPS?  as there can be audio issue when changing frame rates as the HDMI link can be reset for a short period.  If so you could also try Options--> Video--> Display Settings --> Wait after change (try 2 sec).

Also I'm not sure about how "Play silence at start for hardware sync" ment to work, as I just tried it and did not really notice any "silence" regardless of the setting (well maybe a sub second difference even when set to 45 Sec).

The files are always 24fps. Tried at 45 secs does nothing.
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jmone

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #8 on: March 10, 2023, 07:46:20 pm »

Looks like it is time to post a log for the JR'ers to look at!
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murray

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #9 on: March 10, 2023, 07:49:15 pm »

If that does not work then Turn On logging (Help --> Logging) play the offending clips, stop playback, post the Log here, then turn off logging again.

Just done the log. There are three short files mkv all 2 channel 24fps. There are two very loud 2sec screeches between two of the files but it happens between any file when bitstreaming. Set JR to PCM and no screeches between files, but then I have no Atmos.
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jmone

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #10 on: March 10, 2023, 08:26:34 pm »

....just for testing I'd suggest taking the Vertex out of the loop.
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murray

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #11 on: March 10, 2023, 08:29:23 pm »

....just for testing I'd suggest taking the Vertex out of the loop.

I had exactly the same issue when there was no Vertex :(
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jmone

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #12 on: March 10, 2023, 08:37:17 pm »

OK - lets wait and see if there are any hints from the Logs that the JR'ers can see.
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Hendrik

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #13 on: March 11, 2023, 01:25:16 am »

There is nothing suspicious on our side. Video doesn't even have gapless playback that might somehow screw up. Between files we literally close and re-open the device in the new mode. If the AV receiver does not handle that quickly enough, sounds like you should inquire with them.
Its also not an issue I have heard of before.

Silence on startup is not something I would generally recommend with bitstreaming, as we can't play silence in a bitstream, since we can't generate bitstreams. I'm not sure if we entirely disable that function, or it just plays PCM, either way it would not help to actually give the device time to switch to bitstreaming, as there is no bitstream data yet.
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jmone

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #14 on: March 11, 2023, 03:19:40 pm »

Murry, out of interest.... It seems that you only get the screech in a playlist in between tracks and not at the beginning?  If so, how long does the gap need to be to prevent the screech.  Eg if you play a track stop leave it for X seconds and play the second track at what point is it all OK?

Edit - I also see in the manual for the MX160 it has a "Fade In" option that "Prevents abrupt changes in volume at the start or end of a sound track" that may be worth toggling to see if that helps or not.
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jmone

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #15 on: March 14, 2023, 06:33:16 pm »

Update from Murray after trying different sources, inputs, applications and taking things out of the playback chain.... it's the Vertex (a splitter) - it was configured to drive 2 screens and as a HDMI Audio Extractor to the amp.  No probs at all with it pulled out.  He is going to try a different splitter.

Thanks all for looking at logs etc.  One for JimH's weird and wonderful thread.
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JimH

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #16 on: March 14, 2023, 07:18:09 pm »

Good news!  Thanks!  Added it.

Well done, jmone.
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murray

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Re: SCREECH when switching between PCM & Bitstreaming Atmos
« Reply #17 on: March 15, 2023, 01:27:59 am »

Good news!  Thanks!  Added it.

Well done, jmone.

Amazing, and expensive Vertex was the problem causing the horrible Screech when starting any file when bitstreaming. What fixed it was replacing it with a Blustream 1x2 splitter, amazing! Nathan kept me on this with many different tests, his hunch was right!
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