>> Many time I stumble on the issue that the exported frequency response from a clio
>> measurement do not import properly in FIR Designer, so I have been using the time
>> response instead. But now someone sent me some data and I get the same issue. Can
>> you explain if there is a work around to import the measurement properly? It looks
>> like an issue in the phase, see attached .txt. I am running FIR Designer M 2.6.0
>> Thank you so much
Transferring measurements as Freq|Mag|Phase for subsequent filter design is generally bad practice, especially when there is very high phase slope (as in this measurement). Unless the Freq|Mag|Phase format represents the exact output of a DFT or FFT of the IR, there is always a loss of information (relative to the IR). For this reason we strongly recommend transferring the time IR.
In FIR Designer, since Freq|Mag|Phase TXT files come from many different sources, each with different frequency ranges and spacings (including linear/log), we have a frequency interpolator/resampler that does its best to remap the file’s Freq|Mag|Phase onto the underlying FFT size used in the software – typically length 32768. The problems your are seeing are the limitations of this interpolator/resampler when dealing with high phase slope. (Note: When very high phase slope is present, the phase difference between adjacent input data points could be multiples of 360 deg, and we have no way of knowing the ground truth.)
With this file on FIR Designer’s Import tab, if you turn “Oct smoothing” to 12th octave, the magnitude response gets very close to the raw data. (The measurement’s phase is quite odd; I’ve seen something similar caused by realtime sample rate converters on macOS.)
Regarding VACS (which I also have here), I suspect it’s just plotting the raw values from the file (since it doesn’t need to remap the data).
I hope this helps,
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