[vorbis-dev] Specification documents

[Henning Jensen]

Hi everyone,

after having an extensive look at the reference decoder as well as the
specification documents, I'd like to point out what I think to be some
minor omissions/flaws in the latter, and suggestions for correcting them.


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#1:
in vorbis-spec-floor1.html, packet decode:

Between 14) and 15) a crucial step is missing. Please insert:
14a) [cval] >>= [cbits]

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#2:
in vorbis-spec-floor1.html, curve computation step #1:

The distinction between [floor1_Y] and [floor1_final_Y] looks invalid.
IIRC the prediction loop works as follows:
At the beginning Y[0] and Y[1] contain the absolute amplitudes (log scale)
at the lower resp. upper X boundaries, and the Y[i] for i>=2 are the
wrapped difference values, which are then progressively replaced by the
predicted absolute amplitudes at X[i]. In the current spec docs
render_point always takes its input from [floor1_Y] (which mostly contains
differences) and [predicted] then is output into [floor1_final_Y], without
any feedback. IMHO this doesn't work out.
Either the distinction between [floor1_Y] and [floor1_final_Y] has to go
away, otherwise the following may do the trick:

move steps 25) .. 28) to the top, e.g. behind step 1)

in step 5) (but not in step 6) replace the two occurrences of
[floor1_Y] with [floor1_final_Y].

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#3:
in helper.html, function render_line:

Replace 11) with
11) [ady] = [ady] - abs ( [base] ) * [adx]

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That's all I can think of at the moment. Any comments?

Henning

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