Re: [Sursound] an exploratory mail
On 21/01/2013 23:51, Gabriel Wolf wrote: ... Ambisonic's problem was that people were happy, a posteriori, to agree that AMB was inadequate, but were unable to agree on what a proper HOA format should comprise, except inasmuch as plain old 3rd order 3D (the maximum AMB supports) was not good enough. Not good enough in terms of ...? It only supports up to 3rd order periphonic (16 channels), as it relies on the number of channels (avoiding the need to store empty channels) being unambiguous, for each combination of horizontal and height orders, as they are up to that limit. It also presumes the conventional 3dB scaling of the W channel as per the original B-Format spec, and that is now regarded as both inconvenient and obsolete. A proper file format for HOA needs metadata in the header detailing the nature of the encoding, agreed channel orderings and idents (especially where unused channels are omitted). The AMB format has no metadata, just a WAVEX GUID identifying the format. Put most simply, the file header needs to supply all the information required to enable an appropriate decoding to be used. The file is fully self-describing, robust and unambiguous, so that any program can confirm purely by reading the header that the file is properly constructed, and can selectively extract whatever metadata is provided. Ideally it also needs to be efficient in storage, by excluding any unused B-Format channels. One solution that has been defined is to rely on lossless compression to do this, i.e. incorporate the compression into the file format definition itself. Also, AMB is based on the standard WAVE format with 32bit chunk sizes, so is only able to handles file sizes up to 4GB, which is seriously limiting for HOA with high-resolution samples (all the more so if empty channels are included). This was reasonable enough back in 2000, when the WAVEFORMATEXTESNIBLE format itself was very new, but is a serious limitation today. So, defining such a format is non-trivial, even if the core issues are clear. There are so many options, and nobody working in HOA (which as this list demonstrates continues to be a heavily research-active topic) really wants to have to deal with file format limitations. I would guess that MPEG will want a much narrower specification, and maybe base it on some patentable compression scheme, not least as their target speaker arrangement is ostensibly fixed. Whereas a defining characteristic of Ambisonics (HO or otherwise) is that while there are more or less optimum layouts, speaker arrangements are not fixed. In practice, those defining such a format need not only to define the file format itself, but also define and publish basic tools to create/encode and decode, to a suitably wide range of representative speaker arrangements; and of course to be able to confirm the whole thing with listening tests. As well as expertise, that requires considerable physical resources, to say nothing of the generation of source material for test purposes. One way and another, it is an expensive business! Richard Dobson ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] an exploratory mail
Gabriel Wolf wrote: In practice, those defining such a format need not only to define the file format itself, but also define and publish basic tools to create/encode and decode, to a suitably wide range of representative speaker arrangements; and of course to be able to confirm the whole thing with listening tests. As well as expertise, that requires considerable physical resources, to say nothing of the generation of source material for test purposes. One way and another, it is an expensive business! The beautiful double blind listening-test proof (very) HOA format maybe never will make it. An old WAVEEX based thing is also out of discussion. How about a thing in between? A quick and dirty we can do it 'till april-ambisonics that covers already made .amb recordings up to third order and some additional screen and LFE channels? What about ambiX? Franz Zotter reading? :) I think it doesn't work like this . The basic discussion would be if a soundfield approach should be included. After, you would define the details: Order, included direct front channels /LFE channels, file format etc. Why are you actually not reading what I was posting? One of the requirements is arbitrary speaker layouts. Full stop. (There will be some fixed layouts, I guess. But still.) MPEG-H 3D Audio is envisaged to provide a highly immersive audio experience to accompany the highly immersive experience provided by MPEG-H HEVC. Such an immersive listening experience will be realized by the rendering of a realistic and compelling 3D audio scene either by using a large number of loudspeakers, such as for 22.2 channel audio programs, or by using headphones supporting binauralization. Key issues to be addressed are a compact and bit-efficient representation of multi-channel audio programs and the ability to flexibly render an audio program to an arbitrary number of loudspeakers with arbitrary configurations. 3D Audio support via headphones is also a key capability in order to deliver an immersive experience for users of mobile devices. A final CfP will be issued at the 103rd meeting in January 2012, Don't speculate too much around, just do read . Best, Stefan Schreiber P.S.: I know why I copy and paste such things. Dolby Atmos also covers arbitrary speaker layouts, BTW. We are talking about the reality, which is already being implemented. ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] A proposal for an Ambisonics based 3D audio codec, MPEG/ITU style...
Marc Lavallée wrote: Stefan, I was not stating that MPEG and ISO are evil. As a hobbyist, my question is: how Ambisonics might be included in a standard format made by the industry for the industry, that everybody would then have to use if there are no viable (and simple) alternative appart from the AMB format. I can only wait and see. -- Marc You don't have to use any standard. But I see that especially MPEG has defined standards which are used pretty everywhere, included in the freeish Android OS based on Linux and Java. Clients wouldn't buy phones which don't support MP3 or AAC or AVC codecs, every single one is a MPEG standard. You could replace these maybe with Vorbis/Opus/ or Daala video codec (to be defined), but sometimes the first solutions will stay because people don't bother. But at least you see that I am informed about the free competition, if citing topics like Daala etc. :-) At first you need a real standard for 3D audio, I would say. (Dolby Atmos won't do it for home use, UHD TV etc.) Best, Stefan P.S.: FLAC was the first widely used codec for lossless compression, so here the commercial competition has a problem. ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
