Re: How to build a flat-phase DSP preset?
Perhaps some one can shed some light on pre-ringing. I'm aware there are various methods of minimizing rining but never bothered to investigate them in detail. I was stuck with what my Lake Contours could do…. so there wasn’t much point investigating further. (They offered brick wall and 24 / 48 dB FIR linear phase options as well as the standard IIR filters.)
Most of the stuff I can find, is about filters used in DAC’s
http://www.wolfsonmicro.com/documents/uploads/misc/en/Ultra_High_Performance_DAC_whitepaper.pdf
I may be wrong, but I also understand that pre-ringing in adjacent pass bands is equal and opposite, so it should be possible to cancel it acoustically.
These guys (below) seem to suggest you can … (Q9)
http://webcache.googleusercontent.com/search?q=cache:gvTYh2VKX88J:http://www.deqx.com/techquest.php+linear+phase+crossover+pre-ringing&hl=en&gbv=2&gs_l=serp.12...8469.10344.0.12328.10.10.0.0.0.1.266.1280.0j1j5.6.0...0.0.Ce8no6dW7B4&ct=clnk
The plots I posted above used FIR filters, although everything hung together on and off axis very well, the polar response was not so good, and it had a total latency of about 17.7ms . The "production version" of the settings used IIR filters for the sub crossover and 24 & 48 dB linear phase filters for the mid and HF crossover. The FIR time was only 2.5ms.
It’s relatively easy to produce a “flat” frequency and phase response at one point, the hard bit is getting it all to work on and off axis as well maintaining good pattern control through the crossover region. As Bennett, mention you can overlap bands to control directivity … here is one method …
http://www.four-audio.com/data/AES32/html/img15.html
