[LAU] Subject: Albums under a label recorded and/or mixed with Linux

[fons at kokkinizita.net]

On Tue, Sep 28, 2010 at 05:51:09AM -0700, Patrick Shirkey wrote:

> > My issue is that it has an awfully bloated filter (which is suboptimal
> > according to fons) taking up a lot of cpu-power, while for me it could
> > perfectly to with a parametric eq (either three bands + shelve or four
> > bands).
> >
> 
> Ok, Thanks for the clarification.  I am pretty sure you know already that
> there are two eq modes in jamin? 30 band multi and 3 band parametric with
> shelves. However there is not 4 band. It wouldn't be that hard to add
> though if you are serious about it as the three band code is a good place
> to start.

> Now I am not sure that the 3 band parametric should be considered a *real*
> parametric or not.

Certainly not. The curvers are different and it's linear-phase while
a normal parametric would be minimum-phase. Also in the LF end the
curves don't correspond to what is displayed for the simple reason
that the FFT filter can't generate them. The same is true for the
30-band EQ (since it uses the same code).

> However I have been told that the implementation of the
> linear filter in jamin is fundamentally correct as the FFT/IFFT approach
> is the preferred implementation to obtain a more idealized functionality
> of those forms of EQ without screwing up the phase.

The implementation is fundamentally wrong. Just send a sine wave through
it, measure the result and ask yourself how a *filter* could ever produce
the broadband junk that this one is adding.
A correct implementation of the same filter, still FFT-based, having exactly
the same controls, and being able to produce exactly the same frequency and
phase responses would use much less CPU, and not add this distortion.
 
> Fons has cause for suspicion about the current optimisation. It may turn
> out that it is possible that we could shave off some cpu cycles. Perhaps
> we can get to the bottom of that problem, but as we are using these large
> windows to increase the smoothing across the bands(?) it may be that there
> is no further optimisations that can be achieved.

My concerns are not about the optimisation. For there isn't any. I repeat:
the implementation is fundamentally wrong, the method used does not only
filter but it also adds distortion, and most of the CPU power used by the
filter is used just to reduce the problems that result from this.

Ciao,

-- 
FA

There are three of them, and Alleline.