[vorbis-dev] Specification documents

Monty xiphmont at xiph.org
Tue Sep 10 00:54:18 PDT 2002

On Tue, Aug 13, 2002 at 05:09:07PM +0200, Henning Jensen wrote:

> #1:
> in vorbis-spec-floor1.html, packet decode:
> Between 14) and 15) a crucial step is missing. Please insert:
> 14a) [cval] >>= [cbits]


> #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].

I opted for the latter strategy as I dislike the idea of vector
mutation in the spec (as opposed to generating values into new working

> #3:
> in helper.html, function render_line:
> Replace 11) with
> 11) [ady] = [ady] - abs ( [base] ) * [adx]

Also corrected.

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

There's not much to add.  Your concerns and solutions were all precise
and correct.  I'll commit the fixes to CVS and web as soon as I'm
online again (this email will probably flush shortly before the
changes are visible).

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