[linux-audio-dev] jamin and FFT filtering

[Steve Harris]

On Tue, Aug 10, 2004 at 11:25:15AM +0200, Alfons Adriaensen wrote:
> ISTR (from Karlsruhe) the FFT method was chosen because it was
> convenient for two reasons:
> 
> - the bandsplitting and EQ can be combined,
> - the filter response curves can be 'interpolated' easily
>   during scene changes.

Yup, thats pretty much it.
 
> But I'd like to raise another point. Why should these filters
> be 'linear phase' ? The widespread belief that LP filters
> always sound 'better' has been questioned long ago (by Michael
> Gerzon and others).

At the time I started working on jamin, LP filters were the fashionable
thing in mastering software. It didn't seem like a totally bad idea, and I
allready had the code, so I went that way. I had a plan to also offer
parametric IIR's as an alternative, but the EQ UI has grown to the point
were users would loose a lot of functionality if they chose IIRs.
 
> The reason seems to be their symmetry in the time domain,
> giving a long 'pre-ringing zone' before the central main peak,
> It seems human hearing is very sensitive to this 'pre-ringing',
> in particular on transient and percussive sounds.

Yep, we have heard this on some material where you have sharp diconnects
in the gain of adjacent bins, particularly in the low frequencies, it can
be moderated by increasing the overlap, but I dont really understand why.
The effect is not often very noticable though.

- Steve