[Vorbis] Floor1 doubts...

[xiphmont at xiph.org]

On Tue, Nov 10, 2009 at 9:44 PM, Eldhelrim <eldhelrim at gmail.com> wrote:
> Hello,
>
> I've read in a thread from this mailing list
> (http://lists.xiph.org/pipermail/vorbis-dev/2009-September/020019.html) that
> the usage of FLOOR1_fromdB_LOOKUP table is to convert Floor1 values from a
> dB scale to a linear scale. In a dB scale, given a reference value, the
> other dB values are obtained from it, normally dB_value = 10log(p1/p0),
> where p0 is the reference value.
[...]

This mostly restates the same idea several different ways that are
equivalent and I'm not sure where you're confused.  So let's step back
a second...

The floor encodes a continuous function and the values of that
function are meant to be used as multipliers/ratios.  Linear floor
multiplied by residue gives you a spectrum.

The floor is encoded on a logarithmic scale (not actually decibels in
fact, but decibels are easy to understand, so the spec discusses this
in terms of decoding the encoded floor to decibels, then doing a
decibel->linear conversion).  Unitless decibels are just ratios.  1 ==
0db, 2 == 6dB, 4 = 12dB. The coversion is a simple 20log10(linear).

Is that helpful?

Monty