Minimum phase vice versa minimum phase

uli.brueggemann@freenet.de (Uli Brueggemann) wrote in message news:<c77c52c1.0411030617.50bef889@posting.google.com>...
> Hello Rune,
> 
> > I am not completely sure what you mean here, I think you mean what I 
> > would term "mixed phase". Minimum phase has nothing to do with causality, 
> > since this aspect of the phase response is giverned by zeros in the 
> > transfer function. Causality is caused by the poles of the transfer 
> > function being located inside the unit circle. A completely different 
> > thing.
> 
> Linear phase filters with the symmetric structure are described e.g.
> in dspguide as non-causal. If you consider the center as zero then the
> left sided taps are negative. This cannot happen in nature of course. 

Nope. What you describe is a zero phase filter. Causal linear phase 
filters can easily be implemented.

> > > I read that the
> > > minimum phase extraction can also be done by some kind of Hilbert
> > > transform. After applying a FFT to the result I expect to be able to
> > > calculate again magnitude and minimum phase response.
> > 
> > Where did you read that? The "easy" way of finding a minimum phase 
> > response to your system, is to use an AR method to model your system.
> > This will produce a system filter that is minimum pase. The problem 
> > is that many physical systems are mixed phase, so that these naive 
> > ideas don't always work. There was a couple of guys who investigated 
> > mixed/phase parameters a few years ago, try to search for authors
> > Milton and Ursin in the seismics literature. 
> > 
> 
> in a book about loudspeaker measurements of d'Appolito.
> In comparison to the filter design here we get the impulse response
> from a measurement. The room response contains now a minimum phase and
> an excessive phase, maybe we can say in total a mixed phase. I want to
> extract the minimum phase. Several audio measurement software packages
> can do it, but I don't know how.
> 
> What is an AR method?

It's a somewhat advanced method for representing measured data in terms 
of minimum phase filters. Learning these types of methods usually requires 
an at least one semester long intro course on DSP. I haven't heard of 
anyone without a degree in statistics or maths who have read up on 
these things outside a course.

Rune