Support Forums › Forums › FIR Designer Support › how would I do this › Reply To: how would I do this
The actual use case would be near zero degrees at 80 hz crossing to almost
180 degrees at 120 Hz, a fairly steep change of phase….. This response is
easy to create by summing a 100 Hz low pass filter with a 100 Hz high pass filter.
2nd order LP and HP filters have a 180 deg phase change but it’s quite wide – over 4 octaves. The phase change you’re after is very steep and will result in a fairly long impulse response.
There’re two ways you could try to achieve this.
– On the FIR Phase Adjust tab, put a minimum phase 1st order all-pass at ~100 Hz and then use multiple 4th order all-passes, either side of 100 Hz, to tighten up phase slope. Or..
– On the “Input” tab, clear the response, make a 3 column TXT file – freq(Hz), mag (dB, all zeros) and phase (deg) – with your desired phase transition, load the file on the “Target->File” tab (and make sure to un-check “Mag only”), use the “FIR Auto Phase” tab to push the impulse (from the “Import” tab) towards your target phase response, then on the “Export” tab, adjust the length and delay until the error is low.
Best regards,
EA Support