TOPIC:

Hi devs,

I started experimenting with HA-DSP on implementing crossfeed. The first thing I've realized is that a lot of classic crossfeed filters (e.g. Linkwitz (not to be confused with his crossover filters), bs2b, Meier) have non-flat group delay to emulate the delay of sound coming to the opposite ear. When crossfeed is implemented using IIR (recursive) filters, this is easily achieved (see bs2b.sourceforge.net for an example).

But FIR filters have linear phase, and thus group delay is uniform. And I'm not yet aware of technics that would allow making a non-recursive filter with non-uniform group delay.

On the contrast, designing an IIR filter with non-uniform group delay is easy. So I would propose to swap the types of filters used for the EQ and crossfeed sections in HA-DSP. I would use one FIR section per channel for implementing headphone compensation curve, and then two IIR sections per channel for implementing crossfeed.

So I would like to hear your reasoning behind the current signal flow in HA-DSP, and whether it makes sense to change it using my proposal.

Thanks!

Hello Naganov

FIR is not limited to linear phase. In fact you can target any kind of transfer function with FIR (granted enough taps are available), and any type of magnitude-phase relation.
Try rePhase or any of the other recommended FIR tools to get a picture of what can be done with FIR.

Thanks! I'm a beginner in DSP, and all the introductory texts on DSP I've seen were explaining basic FIR filters that have linear phase. I'm glad to know that there are more advanced ones. I will keep looking! Thanks for your support!

@ naganov

we indeed used FIR as it's easiest to implement with say some HRTF database (see CIPC or ircam). These are plug&play.
Wiht this said, it's indeed true that basic crossfeed can be done way easier..

We'll put it as good feedback for an upcoming easier plugin.

DevTeam

Cross-feed newbie here...
Are there any good resources on cross-feed algorithms/filter sets/recipes and how efficient/realistic/non-intrusive they are ?

Take a look at this paper which takes on a broader topic of "stereo widening" (Stereo widening system using binaural cues for
headphones): citeseerx.ist.psu.edu/viewdoc/download?d...97&rep=rep1&type=pdf

Also there is a nice writeup by John Conover citing earlier analog implementations: www.johncon.com/john/SSheadphoneAmp/index.html

...and you can also take a look at the discussion of a crossfeed plugin for Foobar audio player: hydrogenaud.io/index.php/topic,90764.0.html

Hope this provides good starting points.