[Bug 794411] gstaudioresample: insufficient anti-aliasing

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=794411

--- Comment #3 from Aaron Viets <adviets at uwm.edu> ---
Created attachment 369920
  --> https://bugzilla.gnome.org/attachment.cgi?id=369920&action=edit
Transfer Function for audioresample

I used a command line similar to this to generate the data for the attached
plot:

gst-launch-1.0 audiotestsrc num-buffers=100 samplesperbuffer=16384 wave=5 !
audio/x-raw,format=F64LE,rate=16384 ! tee name="teeAB" silent=false !
audioresample quality=9 name="B1" ! audio/x-raw,format=F64LE,rate=2048 !
audioresample quality=9 name="B2" ! audio/x-raw,format=F64LE,rate=16384 !
identity name="B3" teeAB. ! identity name="A1" A1. ! lal_nxydump ! filesink
location=data.txt async=false B3. ! lal_nxydump ! filesink
location=resampled_data.txt async=false

The plot is a transfer function (magnitude and phase) between white noise
produced by audiotestsrc and the same data after it has been downsampled from
16 kHz to 2 kHz and then upsampled back to 16 kHz. The magnitude plot shows
that the signal is significantly attenuated below the Nyquist frequency of 1
kHz. (So perhaps I should clarify that the systematic errors I observed were
not likely due to aliasing, but rather to this extra attenuation.) Is this
attenuation intentional, and if so, is there a setting that will not attenuate
the signal much below the Nyquist rate?

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