QUAD-FLACs are not in 4.0 but in 5.1

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razi

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Sep 26, 2019, 10:00:45 AM9/26/19
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Hi friends, since I´m a pensionare I have a bit more time to arrange my music-library. By this I noticed, that a lot of my multichannel-quad-files are not in 4.0 as aspected but mostly in 5.1.
Does anybody have an idea, what was the reason for that in former time? Imade, as an example, with ffmepg a channel-rearrangment in this way:

ffmpeg.exe -i "E:\DATEN\Downloads\Vom HUB\_SHARE\+++ Multi-Ch +++\VA - Surround Master [FLAC 5.1 24-96]\101 Strings - Bacharach Webb.flac" -filter_complex "channelmap=map=FL-FR|FR-FL|SL-SL|SR-SR:channel_layout=quad(side)" new.flac
 -or-
ffmpeg.exe -i "E:\DATEN\Downloads\Vom HUB\_SHARE\+++ Multi-Ch +++\VA - Surround Master [FLAC 5.1 24-96]\101 Strings - Bacharach Webb.flac" -filter_complex "channelmap=map=FL-FR|FR-FL|SL-BL|SR-BR:channel_layout=quad" new.flac

I think, it depends on your speaker configuration, what kind of mapping you will use. I tried both and doesn´t hear differences.
A reason could be, that my AV-receiver switched the BACK-channels to the SIDE-channels. My speaker configuration is as follows: 5.1.4

A further positive result is, the the space you need will reduce: 1.633.762.617 Bytes --> 1.175.328.464 Bytes in my example.

The topic above is about PCM (mostly FLAC), but it seems, the are similar files in DTS, but there would it be a bit more difficlut ...

Who has more background knowledge in this field?

Razi

cepl...@aol.com

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Sep 26, 2019, 10:37:00 AM9/26/19
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Razi, 

    It is possible that some of the programs used to generate these files generate a center channel and an LFE channel, regardless of whether there is any audio present on those channels.  In other cases, someone might have felt the need to generate a center channel from the front L and R, and maybe also generate a sub channel.    whatever the case, I would recommend you keep everything "as is" and not alter any of your files, as they may not play back right in the future (I've made this mistake).  

 - CP


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razi

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Sep 26, 2019, 12:05:12 PM9/26/19
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Thanks CP for your answer.

Of course, I checked before, that there was no CENTER and no LFE in this files. There wasn´t.
Good to know, that this rearrentgement could be a mistake. But I can´t it hardly believe it.
What was wrong, was the "wrong effect"?
Of course,
one of my mediaplayer (MED800X3D) connected with my ARV (AVR-X4400H) shows the rigth channel-format: 4.0
the other mediaplayer (Dune HD SOLO LITE) showswith the same file with the same AVR the yet "wrong" channel-format: 5.1
I was a bit woundering ....
 - CP


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DanielTheGreatAu

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Sep 27, 2019, 1:51:59 AM9/27/19
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Razi,

Not directly answering your question, but some related information that might be of interest...

Because of my streaming hardware (Squeezeboxes), all my surround music must be encoded into two channels – so DTS or DD.  Of course I always use DTS due to its technical superiority.

I receive surround music from many people in many forms, sometimes even as separate WAV files, one per channel.  Sometimes these have been transcribed from CD-4 records, so contain only four channels of audio, but the suppliers sometimes provide six files, with empty (flat-line) centre and LFE files.  I once asked a supplier why they provide these empty channel files, and he said that some DD decoders will not decode rear channels unless a C channel is included (even if silent).  I would consider this a hardware bug, but have never encountered it since I never use DD.

Initially, if I discovered that the C and/or LFE files were silent, I would delete them before encoding with SurCode.  But once I conducted a simple experiment to see if it made any difference...

I first encoded to DTS one music track using all six WAV files, even though C and LFE were silent.  Then I deleted the C and LFE files and encoded to DTS again.  Both DTS resulting files were exactly the same file size.  And of course both sounded the same since the C and LFE channels were silent or absent in both cases.

So now I don't worry about checking for empty channels, since it takes no more space on my HDD, and makes no difference to the sound! :-)

DanielTheGreat

OkAtanAdam

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Sep 27, 2019, 4:26:05 AM9/27/19
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Razi,

I used to encode 4.0 streams into into 4 channels FLACS until I noticed that some AVRs or Audio Cards would decode the 2 surround channels as Center and LFE instead of SL and SR,
Mapping usually goes as: Channel 1=FL, Ch 2=FR, Ch 3=Center, Ch 4=LFE, Ch 5=SL and Ch 6=SR,
Some decoders would see 4.0 stream as Channels 1-2-3-4, instead of 1-2-5-6,
So in order to insure compatibility with most (Older?) audio decoding systems, I resorted to forcing the 5.1 channel layout when encoding 4.0 streams in FLAC format,
That's the historical idea behind the 4.0 in a 5.1 container, 
Now, how does that affect the newer 5.1.x audio systems, I don't know, I'm not there yet ! :-)

Regards.

gmail

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Sep 27, 2019, 5:20:20 AM9/27/19
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Hi OkAtanAdam,
thank you for this information,  now I know the reason for that phenomen.
It's a shame as I noticed, some (even newer!) devices (my mediaplayer Dune HD SOLO LITE)
akts even today in a wrong way. Maybe is the build-in chip responsible for that.
But I don't know ....

Razi

gmail

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Sep 27, 2019, 5:57:04 AM9/27/19
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Hey Daniel,

maybe you are right, but I ment PCM (lossless FLAC) and not DTS/DD (AC3).
But the reason could be similar (a former FLAC-Decoder? ).
In my cases thee is no CENTER & LFE afterwards reencoding with ffmpeg.
But it's a shame to waste space on HDDs/NAS because of not properly working software.
Today I would say: "Greetings from Microsoft" ... it's always the same....

Regards,
Razi
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manxminx

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Oct 1, 2019, 10:58:00 PM10/1/19
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I have a different explanation . . .  I'm presently listening to The Chicago Quadio set. If I look at the properties of a track in Foobar I get . .

Duration : 4:00.824 (23 119 104 samples)
Sample rate : 96000 Hz
Channels : 4: FL FR SL SR
Bits per sample : 24
Bitrate : 5370 kbps
Codec : FLAC
Encoding : lossless
Tool : reference libFLAC 1.3.1 20141125
Embedded cuesheet : no
Audio MD5 : C5005F9C6A15A3429B0C007AC401BA2B

I've highlighted the relevant part.  It would appear that the channel layout is encoded into the actual track properties (metadata). It took me ages at first to figure out why rear channels were sometimes playing on the side channels instead of the rear. I've since created a button in Foobar which changes the channel layout Side > Rear. All the multi-track albums I've got which play rear on the side channels have this set in the file properties, those albums which play correctly state "4: FL FR BL BR" in the file properties. Out of interest, 5 channel files state : "Channels : 5: FL FR LFE BL BR" or "Channels : 5: FL FR FC BL BR" with 6 channel files stating: Channels : 6: FL FR FC LFE BL BR

This is with both Flac and wav files -  the channel allocation metadata in the file properties is part of the flac standard. See https://xiph.org/flac/format.html#metadata_block
I can't find any proper documentation on wav metadata, but channel allocation looks to be definitely part of the metadata.

So, what I'm thinking is that when someone encodes a multichannel track into FLAC or rips it to wav, whatever, the channel mapping isn't working properly or is set wrong in the encoder, it may even have been the original software coder who screwed up in the code somewhere.. I've had a good look at the FLAC documentation but can't see where or how to encode channel allocations. There is a setting " --channels=# Specify the number of channels in the raw file. " but nothing about mapping channels. Goodness knows how one sets channel allocation in .wav

Ali.

I don't understand how

gmail

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Oct 2, 2019, 3:45:21 AM10/2/19
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Hi Ali,

I'm not sure,  what the right configuration is, BR-BL or SR-SL. I think, the last one is right.
As I found in older documentation, in QUAD the front-speaker have to stay at 30° and rear-speaker at 120° from middle-line.
So I would prefer this configuration.

In my opinion,  the ripping-software is mainly responsible for set up the right channel-configuration.
Anywhere I've read, that WAV has mata-date too, don't know if it true or not.

Razi


Viele Grüße,
Rainer

JP

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Jul 19, 2020, 10:54:19 AM7/19/20
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Sorry to resurrect this old thread... How did you do the following in Foobar2000 to reassign the side and rear channels?

"I've since created a button in Foobar which changes the channel layout Side > Rear."

How did you do this? I would love to be able to easily reassign the metadata to determine where the channels in 4.0 FLAC are played back. Thank you for any info.

-Jp  
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