#46 About floating point VBR settings...

open
nobody
None
5
2012-02-24
2012-02-24
Elio Blanca
No

I see recent lame releases added support for floating point values for the vbr switch `-V', and the floating point part is used to fine tune the lowpass frequency.
About this feature, is some detail added into the lame tag? I mean, since a modification in the floating point part affects the lowpass freq (which is already stored into the lame tag) is there a particular way for checking if a floating point vbr value was used?

Discussion

  • Elio Blanca
    Elio Blanca
    2013-01-19

    Well, I just found into libmp3lame/psymodel.c how the frac part of the `-V' option gets used by lame-3.99.5.
    I'm having a look at statement 2128 and subsequent ones, trying to understand the code. Now, I see why the sk[] array is made of 11 entries and not 10 as one would expect (it is accessed one position more in statement 2135), what I really can't get is: why the value `-9.5' @ pos 3 ? I expected this array to be monotonic in ascending values, but it is not.
    Further, in statement 2128 you declare two floats `sk_s' and `sk_l'. ( BTW, what do their names stand for? do `s' and `l' stand for short and long (granules)? ) Why do you set start values for them, knowing they will be set a couple of statements below? And why two floats are used if they always get set to the same values (statement 2132 and 2135)?