Sound Transcoding: 6ch into 2ch, LFE, etc.. please elaborate

[Utini 13]

Hello everyone,

I have two ways of connecting my sound system to my TV and wonder which one works best in the combination of how transcoding sound works. So I was hoping for some detailed answers. @cayars

Sound System Option A:

1. Any movie file with all kind of sound details (6ch, DTS, Dolby, AC3, .... what ever I throw at it)
2. 5 GHz ACX WiFi with 1Gbit/s local network and general good signal/speed
3. LG OLED CX TV Emby App
4. SPID/F (Passthrough option in LG OLED CX TV)
5. Sony SDP-EP90ES Sound Processor
6. 2ch Cinch
7. Sony TA-F690ES Stereo Amplifier
8. Speaker Cable
9. 2x Magnat Zero 8

Sound System Option B:

1. Any movie file with all kind of sound details (6ch, DTS, Dolby, AC3, .... what ever I throw at it)
2. 5 GHz ACX WiFi with 1Gbit/s local network and general good signal/speed
3. LG OLED CX Emby App
4. SPID/F (PCM option in LG OLED CX TV)
5. Simple DAC (or basically the Sony SDP-EP90ES with all options disabled to only work as DAC)
6. 2ch Cinch
7. Sony TA-F690ES Stereo Amplifier
8. Speaker Cable
9. 2x Magnat Zero 8

The Sony SDP-EP90ES is supposed to transform the digital signal into the connected output (2.0, 5.0, 5.1,...) without loosing any channels/signals while also enhancing the sound architecture through several options. It also keeps (or adds?) the L.F.E "feature".

It can handle the following inputs:

• Dolby Digital / AC3
• MPEG-2
• Dolby ProLogic
• 24-Bit-DSP

And it will transform/output into 2.0 with  "Virtual Enhanced Surround B" according to the manual on page 13. Page 21 shows the possible outputs.

https://www.sony.com/electronics/support/res/manuals/3862/38628811M.pdf

Now to the actual questions:

Emby transcodes files (and there for sound) automatically depending on which formats are supported by the client.

Since I am using the LG OLED CX TV client, I am guessing this is: AC4, AC3 (Dolby Digital), EAC3, HE-AAC, AAC, MP2, MP3, PCM, WMA, apt-X

In most cases I see it being transcoded into AC3 which is fine because the TV and my Sony SDP-EP90ES support it.

Since I always have SPID/F connected as output of my TV, and since I always use a 2.0 speaker setup, I guess I want to end up with AC3 Dolby Digital 2.0.

1. But what happens with the channels and data from the audio that I can't output due to e.g. missing speakers? e.g. 5.1 TrueHD
2. Are they incorporated into the 2.0 channels?
3. Are they missing because they will be "thrown away"?
4. Are the "info" files in the media which tell the transcoder on how to properly transcode and which data to use and which one to throw away?
5. Does emby transcode audio in "losless" quality?
6. What happens with L.F.E?
7. Does emby already do everything that my Sony SDP-EP90ES would actually do (except the sound enhancing like speaker distance, virtual surround,..)?
8. With "passthrough" on the LG TV I notice that my Sony SDP-EP90ES has L.F.E activated, with "PCM" it is not activated. I guess I should go with passthrough then because some audio part seems to be "thrown out" or missing by the TV? Maybe because 2.0 usually doesn't process L.F.E but my speakers include a sub-woofer. I can tell my Sony SDP-EP90ES which speakers I use so this might be the reason why it includes the L.F.E signal even in 2.0?
9. Is "Sound System Option A" generally the best method I can use with my 2.0 setup or do I then have 2x transcoders/transformers which will completely alter the sound?

Sometimes I feel like using "Sound System Option B" gives me more details and more "3D" compared to "Sound System Option A". But with "B" I am missing L.F.E which sounds really great with "A". So I am unsure if I have set everything correctly or should change something.

Thanks in advance!

 

[Carlo 4330]

Hi,

1. The would normally get audio transcoded to a format the client can use.
2. It will basically always beat least 2 Channels (unless the source is mono).
3. The client doesn't get a choice of formats for things it can't play
4. There are stream types. The container type used (ie MKV, MP4, TS, HLS) dictates the information that will be available, where it will be stored and how to access it.
5. Emby can transcode audio to a number of formats..
6. Depends on format converted to. If the format doesn't recognize it then it will be used to transcode but dropped. (I need to doublecheck this).
7. Honestly do not know as I do not have one or know specifically what it does.
8. The first part sounds correct to me. Try it a couple ways and see what works best.
9. Depends on what you're looking for sound wise. I prefer HDMI connections for audio myself.

How much difference do you see between A & B in use?

[Utini 13]

Good morning @cayars and thanks for you reply,

so I am trying to summarize it all:

In each file is usually a stream type / meta info which dictates how a file should be transcoded (in case it even gets transcoded).
E.g. the file will tell the transcoder how exactly a 5.1 stream should be transcoded into 2.0 stream.
Emby can transcode in several formats but will transcode depending on what the client can use. It will follow the rules of the stream type / media info in the file.
If I select "Passthrough Audio" in my LG OLED CX TV, then emby will transcode in the best possible audio that the LG TV with its connected audio component can work with.
In my case that is "passthrough audio" via SPDI/F which should results in Dolby Digital 2.0 / AC3 at highest possible bitrate and with support up to 5.1.
My Sony SDP-EP90ES would then receive that 5.1 / Dolby Digital stream and transcodes it into a 2.0 channel stream including all the sound processing settings I select on the Sony device.
I think I can verify this because the Sony device shows how many channels the input stream has and how many of those channels actually are being output.
Also there is nothing in that transcoding/conversation that emby could do better than my Sony device or vice versa because there is a meta info / stream type in the file that tells how to transcode anyway. So both are just basically following a "rule".

Is that correct?

Also I believe the bitrate of the audio is getting way lower after transcoding.
E.g. it seems like the 5.1 TrueHD Stream has 5300kbit/s but after transcoding it's only 600kbit/s.
Is that because I am only have 2.0 channels, so less channels means less kbit/s in total but the amount of kbit/s per channel stays the same?

 

Regarding the differences between "A" and "B": I will have to do some detailed tests. It might be that due to the L.F.E frequency I might miss details because they are not so noticeable due to the more present low frequencies. Maybe it also is because of the sound processing settings I select on my Sony SDP-EP90ES (e.g. speaker distance, virtual surround enhancement,...).

[Luke 37012]

21 hours ago, Utini said:

Good morning @cayars and thanks for you reply,

so I am trying to summarize it all:

In each file is usually a stream type / meta info which dictates how a file should be transcoded (in case it even gets transcoded).
E.g. the file will tell the transcoder how exactly a 5.1 stream should be transcoded into 2.0 stream.
Emby can transcode in several formats but will transcode depending on what the client can use. It will follow the rules of the stream type / media info in the file.
If I select "Passthrough Audio" in my LG OLED CX TV, then emby will transcode in the best possible audio that the LG TV with its connected audio component can work with.
In my case that is "passthrough audio" via SPDI/F which should results in Dolby Digital 2.0 / AC3 at highest possible bitrate and with support up to 5.1.
My Sony SDP-EP90ES would then receive that 5.1 / Dolby Digital stream and transcodes it into a 2.0 channel stream including all the sound processing settings I select on the Sony device.
I think I can verify this because the Sony device shows how many channels the input stream has and how many of those channels actually are being output.
Also there is nothing in that transcoding/conversation that emby could do better than my Sony device or vice versa because there is a meta info / stream type in the file that tells how to transcode anyway. So both are just basically following a "rule".

Is that correct?

Also I believe the bitrate of the audio is getting way lower after transcoding.
E.g. it seems like the 5.1 TrueHD Stream has 5300kbit/s but after transcoding it's only 600kbit/s.
Is that because I am only have 2.0 channels, so less channels means less kbit/s in total but the amount of kbit/s per channel stays the same?

 

Regarding the differences between "A" and "B": I will have to do some detailed tests. It might be that due to the L.F.E frequency I might miss details because they are not so noticeable due to the more present low frequencies. Maybe it also is because of the sound processing settings I select on my Sony SDP-EP90ES (e.g. speaker distance, virtual surround enhancement,...).

Hi, yes it's a combination of a lot of different things:

• What the client device supports
• The media info of the source file
• Any possible client-side or server-side settings that might impact the direct play/transcoding decision making.

[Utini 13]

Sorry to come back to this.

I learned that DD/DD+/Anything Dolby has information built in that is to be used when downmixing multi-channel (e.g. 5.1) to stereo (2.0).

See: https://en.wikipedia.org/wiki/Dolby_Digital#Channel_configurations

Does the transcoding & downmixing of emby take this into account and properly decodes DD multi-channel?

 

I am asking because I want to upgrade/replace my current sound processor (which is meant as a DD Decoder) with a DSpeaker X2 Anti-Mode (which can only process 2.0 PCM).

So I would need emby (or my LG TV) to do the proper transcoding/dowmixing.

 

[Luke 37012]

On 2/4/2023 at 4:38 AM, Utini said:

Sorry to come back to this.

I learned that DD/DD+/Anything Dolby has information built in that is to be used when downmixing multi-channel (e.g. 5.1) to stereo (2.0).

See: https://en.wikipedia.org/wiki/Dolby_Digital#Channel_configurations

Does the transcoding & downmixing of emby take this into account and properly decodes DD multi-channel?

 

I am asking because I want to upgrade/replace my current sound processor (which is meant as a DD Decoder) with a DSpeaker X2 Anti-Mode (which can only process 2.0 PCM).

So I would need emby (or my LG TV) to do the proper transcoding/dowmixing.

 

HI, for server transcoding, yes, although you'd probably want the TV to direct play it if you can.

[Utini 13]

2 hours ago, Luke said:

HI, for server transcoding, yes, although you'd probably want the TV to direct play it if you can.

Yes I usually choose the audio track that can be direct played. Is there an option to tell emby to always prefer that over transcoding? Because it wouldn't make sense anyway to transcode?

[Luke 37012]

@Utini audio track decisions are based on your emby user audio language preferences and not based on whether or not it will transcode. But the idea of doing this has come up before and it is likely that we'll look at improving this in future updates. Thanks.