AC3 to AAC conversion

[Ghitulescu]

Originally Posted by hello_hello

I think the idea behind the wave file channel ordering was simply to increase the number of channels without making too much of a mess.

The original RIFF/WAV specs allowed for this.

Originally Posted by hello_hello

When the two channels in a stereo wave file are left and right, why when you add a third (ie centre) would it be logical to put it in the middle?

No. When stereo appeared (stereo doesn't mean 2 channels but spatial), people put a number of speakers around the listener. It was the need of a researcher and his paper to demonstrate that stereophonic image can be obtained with only 2 speakers. So 3 speakers were a triangle. Like 4 channels in the '70ies were placed around the listener not all in front of him. Therefore a third channel is more logical to be Center-Back rather than Center-Front.

Originally Posted by hello_hello

The wave file format is THE intermediate PC format used when converting between one format and another. Import a 5.1ch AC3 file into Audacity and then do the same for 5.1ch AAC file. They'll both be imported using the wave file channel order.

It is not. Audacity does not need AFAIK to convert to WAV any file it processes. It converts them however to raw (L)PCM which is not WAV.

I wonder how the engineers at Dolby or in Hollywood converted the audio to Dolby 5.1 when WAV lacked this possibility. Hm, Hm, Hm

Originally Posted by hello_hello

I don't know why that needs explaining to Ghitulescu unless some decoders decode use a different channel order and encoders accept different channel masks to define the input channels.

Half-knowing is dangerous, as I see
Channel mask is the MS invention. Dolby had presets: 4 channels could only mean L,R,Ls,Rs, and this could be combined with LFE to get 4.1.

Originally Posted by hello_hello

So your recent efforts to convert 4.1ch audio to 5.1ch audio? That was all Microsoft's fault and nothing to do with your hardware not decoding 4.1ch correctly?

No, the hardware correctly decoded the files that were not WAV, but I could not get there without passing through WAV due to the tools I am allowed to use. 4.1 it is allowed in Dolby Digital (also in real life, as the video part was dolbidised), see above.

[hello_hello]

Anyway......

After a bit more research it seems the info in the post filler56789 linked to is correct, only maybe it's been interpreted backwards.
The conclusions was:
"As already expected, most encoders and decoders use only the "implicit channel mapping"".
However I think it's exactly the opposite. They'll mostly only use the "explicit" channel mapping, because the "implicit" channel mapping implies 3.1ch AAC encoding is possible. The "explicit" channel mapping however only includes a pre-defined set of channel mappings.

The info in the above link refers to "16 available PCE’s" to define channel mappings. The first seven are listed here:
http://spectralhole.blogspot.com.au/...nel-model.html

Just as I thought I was onto a logical explanation it occurred to me there seems to be only one official PCE for 4ch audio, and that's for a 4ch layout consisting of front stereo, front centre and a rear surround channel (the 4.0ch layout mentioned in my earlier post), yet QAAC will still accept and encode the two 4ch QUAD mappings, but not 3.1ch...... there must be a logical reason for that.

[hello_hello]

Originally Posted by Ghitulescu

No. When stereo appeared (stereo doesn't mean 2 channels but spatial), people put a number of speakers around the listener. It was the need of a researcher and his paper to demonstrate that stereophonic image can be obtained with only 2 speakers. So 3 speakers were a triangle. Like 4 channels in the '70ies were placed around the listener not all in front of him. Therefore a third channel is more logical to be Center-Back rather than Center-Front.

I'm not talking about the position of speakers, I'm talking about the physical wave file itself. You can sit on the third speaker for all it matters, but when you add a third channel to a wave file consisting of two channels that'd normally be decoded as stereo, why would you put it in the middle? Why wouldn't you keep the first two channels as stereo channels and add the third channel as a third channel?

Originally Posted by Ghitulescu

It is not. Audacity does not need AFAIK to convert to WAV any file it processes. It converts them however to raw (L)PCM which is not WAV.

Why is it so hard for you to understand a simple point? I never said they're imported as wave files. I said they're imported using the wave file channel order.
Import a 5.1ch file into Audacity and look at the physical order. ie the order the channels appear in the GUI. It's the wave file channel order. It doesn't matter what format you import or the channel order that format uses, they're imported using THE common channel order. The channel order for wave files.
And no, I didn't say they were imported as wave files, in case you're still confused.

Originally Posted by Ghitulescu

I wonder how the engineers at Dolby or in Hollywood converted the audio to Dolby 5.1 when WAV lacked this possibility. Hm, Hm, Hm

I don't know, but you're telling the story and it's not going to be satisfying until we learn how it ends. How did they do it?

Originally Posted by Ghitulescu

Half-knowing is dangerous, as I see
Channel mask is the MS invention. Dolby had presets: 4 channels could only mean L,R,Ls,Rs, and this could be combined with LFE to get 4.1.

Nobody said it wasn't a Microsoft invention, but HHEELLOO!!!!! We're referring to using a PC and for a PC when decoding different formats and/or encoding using different codecs it's standard to use the wave file channel ordering and wave file channel mask as an intermediate format. I've never said anything different.

Originally Posted by Ghitulescu

No, the hardware correctly decoded the files that were not WAV, but I could not get there without passing through WAV due to the tools I am allowed to use. 4.1 it is allowed in Dolby Digital (also in real life, as the video part was dolbidised), see above.

Did you need to convert your 4.1ch files to 5.1ch for you AVR to decode them correctly as per your thread, or was there really some other reason for it you're now only just revealing?

[filler56789]

Originally Posted by hello_hello

........
......
..........

there must be a logical reason for that.

There must be a reason? Surely.
But does that reason have to be *logical*? Not at all.

Human beings are notorious for being illogical and irrational. And unfortunately, becoming a (self-declared) "champion of (PSEUDO-)skepticism and (Illuminist) rationality" invariably only makes the disease worse

[hello_hello]

Well I tried, but so far nothing as simple as "the freeware AAC encoders don't support 3.1ch audio because....." on any web page I've looked at. I still think there must be a logical explanation, if for no other reason than they're all the same. It's not like one encoder encodes it while another won't, but no matter how rational or irrational that reason may be, I'm yet to find it.

[Ghitulescu]

Originally Posted by hello_hello

Did you need to convert your 4.1ch files to 5.1ch for you AVR to decode them correctly as per your thread, or was there really some other reason for it you're now only just revealing?

My AVR works just fine. But I was in need to convert a 4.1 (no centre) audio to something I can use. And ran into WAV peculiarities and software shortcoming.

In case you overthink instead of reading, I changed the player and not double checking some information.

The AAC standard 13818-7 allows for whatever channel combination and order. If one particular encoder does not like a particular configuration it's entirely its (encoder) fault.

In the case of 3.1 the standard does not allow it if the configuration is Left, Right, Centre and LFE the can only be one single channel, and this is the LFE. All others must be paired. The trick would be to allocate two channels (center left and cenjter right) to represent C (dual mono).

[hello_hello]

Originally Posted by Ghitulescu

My AVR works just fine. But I was in need to convert a 4.1 (no centre) audio to something I can use. And ran into WAV peculiarities and software shortcoming.

In case you overthink instead of reading, I changed the player and not double checking some information.

I'm not over-thinking anything. I'm trying hard not to think about your logic behind having to convert formats that you claimed were being decoded correctly.

Originally Posted by Ghitulescu

The AAC standard 13818-7 allows for whatever channel combination and order. If one particular encoder does not like a particular configuration it's entirely its (encoder) fault.

There must be an AAC encoder conspiracy taking place then.

Originally Posted by Ghitulescu

In the case of 3.1 the standard does not allow it if the configuration is Left, Right, Centre and LFE the can only be one single channel, and this is the LFE. All others must be paired. The trick would be to allocate two channels (center left and cenjter right) to represent C (dual mono).

So the standard allows for any channel combination, and if an encoder doesn't like a configuration it's the encoder's fault, except for 3.1ch because the standard that allows for any configuration doesn't allow for 3.1ch. Is that how it works?

That definitely sounds like something you just made up again. How do you explain 5.1ch? Doesn't it consist of 2 pairs of channels and two single channels? What about 4ch? Doesn't it have two single channels? Front left and right (paired channel) plus front centre and rear surround, both being single channels? According to Table 42 on page 61 of this pdf, the 4.0ch configuration definitely contains two single channel elements.

[Ghitulescu]

Originally Posted by hello_hello

I'm not over-thinking anything. I'm trying hard not to think about your logic behind having to convert formats that you claimed were being decoded correctly.

It is a behaviour at you NOT TO understand what is written. I mean to try to twist what has been said in order to make you like having right when you're obviously wrong. I changed the player and the DVD-A was not supported in the new one (although some reviewers mentioned it). DVD-A and SACD are rather dead and toys implementing both are rare. It is my fault for not double checking this. Since I own olny a few DVD-A discs I decided to convert them to a format my new player accepts, either a DVD-V with lossless audio, or a collection of FLACs, rather than to buy a new, universal player, matching my existing rig.
But when the pieces of gear work - they work. They can't afford to wait for a firmware upgrade or to ask for downloading of a new codec or codec-pack as on a computer. They have to work right out-of-the-box. Besides, a 4.1 DVD-A disc would not be sold if this combination of channels would be unsupported by the players it is designed for.

Originally Posted by hello_hello

According to Table 42 on page 61, the 4.0ch configuration definitely contains two single channel elements.

Table 42 reads, for 4 channels, the following and only configuration
4 ¦ 4 ¦ single_channel_element(center front speaker), channel_pair_element(left, right center front speakers), single_channel_element(rear surround).

So it's a 3 center front-speakers and a single rear one configuration. Hardly a real-life configuration (unless one implements true L and R to be stored as LFC and RFC). This is how I read them. I am not sure this configuration has anything to do with your expectations of a 3.1 configuration (most probably L, R, C and LFE).
But this are the implicit/default matrixes. In other words, if you send a 4-substreams file to any AAC-encoder that encoder has to use the default matrix (table 42) to assign the channels.
If you don't want this stupid 4-chn matrix you have to use a custom assignment, as per clause 8.5.3.2. Wherein

Any SCE’s except the last SCE must be paired, and the presence of exactly two SCE’s (alone or preceeded by a CPE) indicates that the two SCE’s are Left and Right Rear center, respectively.

So, you may have: CPEs (already paired) and paired SCEs but only the last SCE in the list may be a "bachelor" (usually LFE).

Because LFE always was a single channel (since Dolby implemented it in 1991).

Why this strange pairing? For encoding economy - in short, pair channels may be encoded as MS (Mid+Side), known as joint stereo in MP3.
Single channels are reserved for channels carrying important information, like L and R, although they can also be present as a pair (probably to allow an even lower bitrate).

[hello_hello]

Originally Posted by Ghitulescu

It is a behaviour at you NOT TO understand what is written. I mean to try to twist what has been said in order to make you like having right when you're obviously wrong.

I understand exactly what's written and I don't need to try to twist anything.
I'm fully aware you had to convert the 4.1ch audio to 5.1ch. I never said you didn't. I just don't know why it requires references to Microsoft when you're using a hardware player and it's got nothing to do with the topic. It's just you once again dragging a thread off on a tangent because you like to pretend you know what you're talking about and you thought my references to the wave file format was an opportunity to display how clever you think you are, only once again you didn't understand what was being said and the result was another of your tangents.
Stating I'm obviously wrong is hilarious coming from you when you've ignored almost entire posts in this thread because they've proved you wrong.

Originally Posted by Ghitulescu

Table 42 reads, for 4 channels, the following and only configuration
4 ¦ 4 ¦ single_channel_element(center front speaker), channel_pair_element(left, right center front speakers), single_channel_element(rear surround).

So it's a 3 center front-speakers and a single rear one configuration. Hardly a real-life configuration (unless one implements true L and R to be stored as LFC and RFC). This is how I read them.
I am not sure this configuration has anything to do with your expectations of a 3.1 configuration (most probably L, R, C and LFE).

Foobar2000 displays 4.0ch audio consisting of a front centre channel, front left and right channels, and a rear centre channel.
Whether it's labelled as rear centre or rear surround I don't see how it's any different to 3.1ch except there's a rear centre channel instead of a LFE channel. It's specified as two single channel elements and one channel pair element, a configuration you said wasn't allowed because only one unpaired SCE was allowed.

Originally Posted by Ghitulescu

But this are the implicit/default matrixes. In other words, if you send a 4-substreams file to any AAC-encoder that encoder has to use the default matrix (table 42) to assign the channels.
If you don't want this stupid 4-chn matrix you have to use a custom assignment, as per clause 8.5.3.2.

So it can use the stupid 4ch matrix despite your claim there can only be one unpaired single channel, or is that somehow still true even while we talk about the 4ch configuration with two unpaired SCEs?

Originally Posted by Ghitulescu

Any SCE’s except the last SCE must be paired, and the presence of exactly two SCE’s (alone or preceeded by a CPE) indicates that the two SCE’s are Left and Right Rear center, respectively.

Let's include the part of 8.5.3.2 you ignored because it didn't suit you.

Included in the PCE are “list of front channels”, using the rule center outwards, left before right. In this list, a center channel SCE, if any, must come first, and any other SCE’s must appear in pairs, constituting an LR pair.

After the list of front channels, there is a list of “side channels” consisting of CPE’s, or of pairs of SCE’s. These are listed in the order of front to back. Again, in the case of a pair of SCE’s, the first is a left channel, the second a right channel.

After the list of side channels, a list of back channels is available, listed from outside in. Any SCE’s except the last SCE must be paired, and the presence of exactly two SCE’s (alone or preceeded by a CPE) indicates that the two SCE’s are Left and Right Rear center, respectively.

Obviously you can start with a non-paired SCE and end with a non-paired SCE and every time I add one single SCE to another single SCE I get two single SCEs. Didn't you say there could only be one?
The default 4ch matrix follows the rule exactly as described. Unpaired SCE (centre), paired SCE(L&R), unpaired SCE (rear).

Originally Posted by Ghitulescu

So, you may have: CPEs (already paired) and paired SCEs but only the last SCE in the list may be a "bachelor" (usually LFE).
Because LFE always was a single channel (since Dolby implemented it in 1991).

The AAC spec clearly distinguishes between a LFE and a SCE so the last SCE in the chain is not assumed to be an LFE channel. That's just something new you've made up. Only a LFE channel is assumed to be an LFE channel.
You only have to think about 5.1ch audio for ten seconds to see your claim makes no sense. Front LR is a pair, rear LR is a pair, the LFE channel is unpaired, so where does that leave the centre channel when there can't be another unpaired SCE? Obviously 3.1ch is the same as 5.1ch with a pair of SCEs removed. How then can 3.1ch not be allowed??

Other elements are also specified. A list of one or more LFE’s is specified for application to this program.

Originally Posted by Ghitulescu

Why this strange pairing? For encoding economy - in short, pair channels may be encoded as MS (Mid+Side), known as joint stereo in MP3.
Single channels are reserved for channels carrying important information, like L and R, although they can also be present as a pair (probably to allow an even lower bitrate).

You sure you're not making it up as you go again? Why have SCEs if they're going to be encoded as joint stereo? It seems more likely that the definition of a pair of SCEs encoded using joint stereo would be a CPE.
And why can't you encode important channels like L and R using joint stereo? Wouldn't that kind of be the point of it?

[tebasuna51]

Please guys let's go.

Last posts are useless for others users.