Floor1 doubts...
Eldhelrim <[email protected]>
| Newsgroups | gmane.comp.multimedia.ogg.vorbis.general |
|---|---|
| Message-ID | <[email protected]> |
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. Supposing p0 is a fixed value, both 10log(p1/p0) => p1/p0 and 10log(p1/p0) => p1 are dB to linear conversions, so, my doubt is: which one of the conversions is done, p1/p0 or p1? Besides, given that the maximum value of FLOOR_fromdB_LOOKUP table is 1, my deduction is that the conversion which is made is 10log(p1/p0) => p1/p0. The alternative would be converting to p1, chosing arbitrarily 1 as the maximum value (in which units?). As I haven't been able to find any reference to this, I tend to believe that the conversion is made to p1/p0... In the other hand, in "Improved Noise Weighting in CELP Coding of Speech - Applying the Vorbis Psychoacoustic Model To Speex", it is said that the floor is a superposition of the tonal and noise masks. So, given my previous supposition of converting to p1/p0, and given that the maximum value in FLOOR1_fromdB_LOOKUP is 1... then, which is the reference value used? I first thought of the ATH (2e-05 Pascals), but, if so, the maximum value for the floor would be the ATH itself, and it seems to me a bit unlikely for the masks to be always lesser than the ATH... So if my supposition of converting to p1/p0 is right, then the alternative must be that p0 is not a fixed value in FLOOR1_fromdB_LOOKUP and it varies somehow. So, I see here two options: that all my suppositions are right, and then p0 varies, in which case, how does it vary? Or, which I think will be the most probable option, I've made some wrong deduction or supposition, but, as much I think of it, or as much I look for any kind of info in the spec, the web, articles... I'm not able to find any answer... I really need to understand this, so, any kind of help will be much appreciated. Thank you very much. _______________________________________________ Vorbis mailing list [email protected] http://lists.xiph.org/mailman/listinfo/vorbis