Hi Sunil,
I’ve looked over the project and measurement files. The measurement is a 3 column freq/mag/phase TXT file with very high phase slope. In other words the impulse response of this measurement wasn’t near time=0 in the measurement system, before the TXT file was exported. (In the excerpt below, the phase starts at -76 degrees and ends up < -40,000 degrees.) The file import process in FIR Designer does it’s best to interpolate this TXT file up to the internal FFT size, but very high phase slope causes errors in this interpolation. And both the interpolation errors and high phase slope are causing the Auto Mag problems that you are seeing.
Two suggestions. Either remove any bulk time offset from the measurement before exporting the freq/mag/phase TXT file, or export the impulse response itself as a time signal – TXT or WAV. With time signals, FIR Designer can remove bulk delay without any response error.
Note that freq/mag/phase files are great for plotting, but inherently loose information*, when compared to the time waveform IR.
* unless they are a linear frequency spaced FFT data.
Frequency Magnitude Phase
20 74.9498 -76.0055
20.3 75.0916 -78.8764
20.6 75.2281 -81.1653
20.9 75.2503 -82.5894
21.2 75.3959 -82.2123
…
18500 88.7457 -40505.1289
18750 88.765 -41041.2812
19000 88.7698 -41577.7695
19250 88.7277 -42114.3984
19500 88.6458 -42650.1914
19750 88.6929 -43186.1406
20000 88.7875 -43758.5703
Best,
EA Support