[LAU] Question about plugin 1970 (EQ)

[S. Massy]

On Wed, Jul 06, 2011 at 09:02:46AM +0000, Fons Adriaensen wrote:
> On Wed, Jul 06, 2011 at 10:24:02AM +0200, Cedric Roux wrote:
> 
> > > I'm using a four band parametric EQ (ladspa 1970) and am wondering
> > > what
> > > manner of units the bandwidth parameter employs. The range is
> > > 0.125-8.
> > > Octaves?
> > 
> > you're sure about the number? I can't see that plugin at:
> > http://plugin.org.uk/faq.php
> 
> It's one of mine, and none of them (1941..1980) is on that list.
> Don't ask me why.
> 
> To answer the original question: the number 1/8...8 is the
> relative (to the center frequency) bandwidth, it is a pure
> ratio and has no physical dimension.
> 
> It is roughly equal to the difference (in Hz) between the
> -3dB points at full positive gain, divided by the center
> frequency. 
> 
> A filter such as this one has actually two damping factors
> in its transfer function, and both can change in function
> of the actual gain setting. So there is no single 'obvious'
> way to define its bandwidth, you need something pragmatic
> such as the definition used here.
What would some good starting point be to experiment with this
parameter? The plugin states 1 as its default, but nama's mastering
chain EQ uses 1/8.

Cheers,
S.M.