Linear-phase brick-wall crossovers

[EA Support]

EA Support

3 November 2024 at 9:02 pm #936

Thank you for your example. I would like to have also brickwall at 300Hz. I see in your FIR Magnitude Adjust you set Bwall, but it doesn’t seem as brick wall in your Auto Mag Filtered response. For 2k it looks as brickwall.

The brick-wall filters have a length parameter, in milliseconds. In my example, both the 300 Hz and 2 kHz crossovers were set for 10ms. 10ms at lower frequencies results in a broad filter than 10ms at higher frequencies, as you’ve found.

I changed FIR Magnitude Adjust Bwall order to 40ms in MF and LF and I got brickwall shape at 300Hz. Is it OK or that 40ms is too high for some reason?

Yes, longer FIR filters enabled steeper crossovers and higher Q filtering at lower frequencies. Please read

FIR Filter Guide

and in particular, sections 4 and 5.

How long is completely up to you, your design goals and the capabilities of the processor you are using. Note that even if your processor supports longer filters, longer linear-phase filters inherently have higher delay (or latency).

Now with that 40ms I see some ripple in Export/Total Error graph around 50-80 Hz. Is possible to flatten that ripple or it is not important?

Yes, by making the filter longer and adjusting the delay.

Is there possible to see group delay of crossover project in your software, I can’t find it ? As I know Group delay is more important for sound fidelity then phase response.

The group delay of the filtering, in each channel, can be view in “Second View” on the “Export” tab “Group Delay” sub tab. Note that it shows the group delay of the filtering, not the group delay of the filtered measurements – which is more important.

However in “Second View”, the “Export” tab “Wavelet Transform” view shows the combined response of the measurements with filtering. An ideal linear-phase filtered response is symetric; wider at low frequencies and narrow at high frequencies. The closer the wavelet view is to symetric, the closer to the ideal, constant, group delay. Note also that the bulk delay shown in the wavelet view matches the delay of the channel whose FIR filter has the longest delay. All other channels are time aligned so that their filter delays all match.