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  • #715
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Issue created Dec 25, 2019 by Peter Körner@MaZderMind

fft: State shared between different instances: creates "crosstalk" when using multiple spectrum elements

I thin I found an Issue with the data separation in the spectrum Element. It can be reproduced with this gst-launch-Line:

gst-launch-1.0 -vm \
	audiotestsrc freq=400 is-live=true ! \
		audio/x-raw,format=S16LE,rate=48000,channels=1 ! \
		identity sync=true ! \
		spectrum bands=600 ! \
		wavenc ! filesink location=/tmp/1.wav \
	\
	audiotestsrc freq=5000 is-live=true ! \
		audio/x-raw,format=S16LE,rate=48000,channels=1 ! \
		identity sync=true ! \
		spectrum bands=600 ! \
		wavenc ! filesink location=/tmp/2.wav

One would expect to see two spectrum-Messages, each showing one peak at the expected frequency. Instead, both Elements report a spectrum with two peaks at the two frequencies:

Got message #192 from element "spectrum1" (element): spectrum, endtime=(guint64)3100140206, timestamp=(guint64)3000140206, stream-time=(guint64)3000140206, running-time=(guint64)3000140206, duration=(guint64)100000000, magnitude=(float){ -60, -60, -60, -60, -60, -60, -60, -60, -60, -40.216724395751953, -36.669300079345703, -40.481967926025391, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -52.428794860839844, -38.907684326171875, -36.817657470703125, -42.258983612060547, -58.275657653808594, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60 };
Got message #193 from element "spectrum0" (element): spectrum, endtime=(guint64)3100138587, timestamp=(guint64)3000138587, stream-time=(guint64)3000138587, running-time=(guint64)3000138587, duration=(guint64)100000000, magnitude=(float){ -60, -60, -60, -60, -60, -60, -60, -60, -60, -31.935056686401367, -26.626094818115234, -32.356891632080078, -58.08837890625, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -52.428794860839844, -38.907684326171875, -36.817657470703125, -42.258983612060547, -58.275657653808594, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60, -60 };

Both peaks in both messages can be spotted by eye, but it becomes even more clear when visualized in a charting tool: Screenshot_from_2019-12-26_00-10-06

Analyzing the written .wav-Files shows, that the crosstalk only exists in the spectral analysis data, not in the streams themselves. I therefore guess that this might be an issue in the allocation of parts of the FFT library.

Edited Dec 27, 2019 by Tim-Philipp Müller
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