Support Forums › Forums › FIR Designer M Support › Linear-phase brick-wall crossovers › Reply To: Linear-phase brick-wall crossovers
>> Group delay in this case is maximum around 2-3ms for HF and around 4ms for MF. It
>> seems too high compared to maximum around 1ms for LR4. According to some studies
>> more then 1ms in area of 500-5000 Hz could be audible. My idea is to make very
>> steep crossover around 72db/octave for both crossover points in 3way and Group
>> delay not higher then 1ms in 50-20kHz band. Could you suggest which type of
>> crossover I should choose. Maybe instead brickwall I should use LR12
The potential audibility of group delay relates to the audibility of the variation in group delay across frequency. Linear-phase filtering inherently has no variation in group delay across frequency; i.e. the group delay of a linear-phase filter is pure delay only.
The Brick Wall set to 20ms should get close to what you need. Also, we provide LR up to 8th order, which is 48 dB/oct. In the Target tab and the Mag Adjust tab, you can combine an 8th order LR with a 6th order LR to give ~72db/octave – both set to linear phase. Or even try the Elliptic filter prototype – set to linear phase – and experiment with the filter order and stop band attenuation to achieve the slope you want.
Remember, the steeper crossover filter shapes, implemented in FIR filters, require longer filters.
As to your requirements, if you set up the processing to essentially be linear phase from 50 Hz to 20 kHz, then any variation in group delay across frequency is essentially zero, but the filtering will have a bulk delay. Again, take a look at the wavelength view to see this.
If you want to use minimum-phase filtering to achieve your goals, I can’t recommend any particular approach. You will need to experiment.
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