>
> :: As a value of 200 for BLACKSIZE showed an improvement in resampling, why
> :: does is still got a value as low as 25?
> ::
> Low pass, high pass and resampling code should be replaced by artefact-less
> program code.
>
Which filters have artifacts?
low pass code is implemented with a very high quality polyphase
filterbank. It is a near-lossless filterbank with a 256 point
window and is claimed to have very good frequency resolution.
high pass filtering: At frequencies above a few hundred Hz,
this can also be implemented with the polyphase filterbank.
Below that, any such filter would require a large window size
and lots more buffering. I think this should be a seperate
utility outside of lame? Most people encode from CDs, which
usually are already correctly filtered for stuff below 20hz.
Resampling: The resampling code does had some minor problems
due to a hack I put in to save CPU time, but this has now
been fixed. There are no more artifacts, but it is unclear
what type of low pass filtering should be done for the
resampling routine: sharp cuttoff or smooth transition band?
Can you explain what you mean by LTI? All the filters in lame are
of course translation (in time) invariant.
> All three are currently done by code not being a LTI system, which results
> in unnecessary distortions. You can see this in the spectral view of
> CoolEdit Pro.
>
> LTI stands for Linear Time Invariant. Non LTI systems are generating
> additional frequencies instead of only emphasing and deemphasing
> frequencies.
>
> --
> Mit freundlichen Grüßen
> Frank Klemm
>
Mark
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