On Tue, 11 Jul 2000, Robert Hegemann wrote:
> I'm a bit worried about LAME's short block detection.
> Consider the following sequence of short block
> energies with a big surge between b3 and b4:
> b1 b2 b3 b4 b5 b6
> <100><100><100><2000><2000><2000>
>
> If the frame boundaries are like
> f1 f2
> [b1,b2,b3][b4,b5,b6]
>
> then LAME will not switch to short blocks, because
> there are no big surges in f1 or f2.
>
Hi Robert,
What you say is true: a surge like that will not be detected
to by the intra-frame energy variation code, but in most
cases it will be detected by a big surge in the PE.
(which is sensitive to frame-to-frame variations)
Surges in PE are the default ISO short block detection scheme,
and LAME uses both PE and this energy variation code.
We added the energy variation stuff to catch pre-echo that
the PE algorithm wound miss.
Mark
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