[vorbis-dev] cascading Ogg Vorbis encoded audio

[Rob Burke]

Monty,

thanks for the quick response....

> > I am planning on doing thesis research on cascading audio encoding
> > chains and how to eliminate or improve audible artifacts in future
> > encoding generations and will potentially be using Ogg for this
> work.
> 
> Define 'cascading' more carefully please.

Sorry, I should have been clearer here.
By 'cascading' I am referring to performing multiple encoding
generations from the original input source.  In other words, taking
your original CD-quality audio and putting it through 20 stages of
coders.

> > My specific question is, Has anyone done any prior work in
> cascading
> > audio encoders?  If so, it would be a great benefit for me to get
> in
> > touch with them or at least read through their work.
> 
> Commenting only from what I can gather through context, 'multiple
> encoding generations is not part of the Vorbis spec'.  If by
> 'cascading' you instead mean progressive encding, the Vorbis encoder
> supports and uses this internally.

Quick question, what do you mean by 'progressive encoding'?  Is that
variable bit rate?  Sorry, I'm not familiar with Ogg Vorbis; I just
found the site yesterday and I haven't looked through it thoroughly yet
so forgive if I'm ignorant with some of the lingo.

By cascading, I meant the following:
16 bit/44.1/PCM -> Vorbis 160 kbps -> Vorbis 128 kbps -> (insert codec
of choice) and so on, perhaps up to 20 different encode stages.  For
right now, I am considering only the Vorbis spec but of course the end
goal is to figure out techniques to reduce audible artifacts in audio
files which have been put through several audio encoding steps,
especially when different codecs are used.  For now, I just want to
look at Ogg since it seems an ideal candidate for an audio encoder. 
But the end goal remains to try and figure out a universal way to make
audio codecs less prone to aural artifacts due to multiple encoding
generations without adding any overhead.

Actually, I am pleased that multiple encoding generations is not part
of the Vorbis spec.  First, I wouldn't expect it too, and secondly,
that is what I would like to look into.  There is a definable meta-data
field in the spec is there not?  Perhaps some information could be
placed in this field which could help future encoding stages keep as
much of the original content as possible.  Possibly putting some
parameters of the psychoacoustic model used in the lossy compression
scheme or something like that.

Anyway, well, I hope to hear any ideas from you all - I will be
actually looking at source code and so forth soon.

Rob

> 
> Monty
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