Hypex DSP module(s)

[Bruno Putzeys]

It's indeed what I would expect. Kudos for writing this software.

[phase_accurate]

Hi Bruno

First of all I'd like to wish you a Happy New Year.

Second:
One transient-perfect opology that wouldn't be too hard to implement is the subtractive-delay one. That would be much easier for the users and the programmer compared to FIR or other pseudo-noncausal methods.

Regards

Charles

[Bruno Putzeys]

Hi Charles, vir jou dieselfde!

So far the subtractive topologies I've seen all trade in phase matching for improved transient behaviour on-axis. I wouldn't know what Psi are doing though, they seem to have figured it out quite well.

[phase_accurate]

Dankie !

PSI is using conventional crossovers and a classic phase-equaliser (built from 2nd order allpass sections) in front of them.

What I meant by subtractive-delay is something like that (second picture of 2nd post):

Problem with subtractor block | EngineerZone

If you use a higher-order Bessel for the lowpass you will end up with quite good phase-matching between the different ways. But the Highpass wouldn't be very steep.

Regards

Charles

[Bruno Putzeys]

Could the same responses not be approximated using the filter/delay functionality in the existing Hypex software?

[phase_accurate]

There is just a tiny little bit that is missing: You would need to subtract an IIR lowpass function from a delayed (but otherwise unaltered) version of the input signal. The delay must be set to the same value as the group-delay of the lowpass at zero Hz.

Filtering and delaying alone wouldn't work.

Regards

Charles

[Bruno Putzeys]

That's why I said "approximate"...

[phase_accurate]

OK, sorry ...

One way to correct such things would be the use of a chain of allpasses but they wouldn't be easy to dimension. I for instance do this with an Excel sheet and some trial and error. But there are of course filter design programs that can do phase-linearisation but they are quite costly, especially if you don't need them too often.

Regards

Charles

[phase_accurate]

This paper here was presented at an AES meeting and shows a method that is a good compromise regarding transient accuracy and frequency response. Unfortunately it also suffers from some lobing issues but less so than the classic constant voltage subtractive crossovers:

http://www.harschacoustic.ch/Crossov...20response.pdf

Regards

Charles

[ds23man]

I also think linear phase is overrated....

We have to see everything in it's perspective. Only a loudspeaker with 1 driver hase a linear phase, if you ad a driver it aint anymore. Phasing will be dependent of listening position and can't be corrected with a filter ( or you should put a sensor on your head attached with your dsp) The only thing you can do is correcting the phase on one position ( aka the sweet spot) and is done with delay. If you change your listening position in the vertical plane, the delay time for the drivers to reach your ears change and so will the phase..... The most important thing in filtering is to get the phase right at the crossover point related to the intended listening position.

The attached picture is from the earlier mentioned linear phase xover, but demonstrates this phase "problem" clearly ( and does not solve it!).