[vorbis] some more Spec questions

[Sebastian Gesemann]

Hi !

<p>I previously posted a mail in the vorbis-dev mailing list because I'm 
trying to implement a vorbis decoder in java from scratch in my
sparetime and have some questions about the bitstream spec.
As I did not get any replies, I got kinda dissapointed and 
demotivated - But now.... I'm trying to take my chances here.
:-)

I'm NOT a newbie to source coding (I successfully coded an MPEG1
Layer II decoder from scratch by the ISO spec draft).
Therefore, the following questions might be quite reasonable.
(...and might be useful for improving the spec?)

<p>Decode setup - Identification header
------------------------------------
- AFAIK Vorbis uses MDCT transforms which will result in 'spectral-
  vectors' of the length 1024 (for long blocks) and 128 (for short
  blocks) at 44kHz, so I expected the two 4-bit exponents in the
  identification header to be 7 and 10, but I found 8 and 11 in
  my Oggs. So the "blocksize" values correspond to the nominal
  window-length instead of the length of the 'spectral-vector' ??
  I find it a bit confusing and inconsistent. (Compare to 'vorbis-
  spec-intro.html': 64...8192 samples/frame)
  I suggest adding a note for clarification.

<p>Floor 0 format - header decode
------------------------------
- Step 7: how could any of those values be less than zero
  if i read them as unsigned integers ?

<p>Floor 0 format - curve computation
----------------------------------
- What is [n] in context of the 'map_i = minimum { ...'-
  iteration ? I tend to think [n] is still the length
  of the final floor vector to be computed and the [map]
  vector is used to map an element of the final-floor
  vector to a bark-scale frequency, is this correct ? 
- The formulas for p and q make use of omega, but there's
  nothing in the spec about omega... How is omega related
  to [i] or to ([map] element [i]) ? 
  I can only assume.... omega = map[i]/bark_map_size ?

<p>thanks in advance,
Sebastian

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