Blue line at 8K, but 8KNotch EQ doesn't remove it

[DL Voice]

I can't hear anything when I'm listening to this particular audio, but I noticed a light blue bar/line in the Spectrogram view around the 8K area. I tried the 8KNotch setting in EQ, but that didn't remove it. Strange.

[Trebor]

I can't hear anything when I'm listening to this particular audio, but I noticed a light blue bar/line in the Spectrogram...

The intensity colour-key is blue-red-white , with blue being quiet , white being loud.

I tried the 8KNotch setting in EQ, but that didn't remove it. Strange.

Have you tried an actual notch filter , rather than creating a notch using the EQualizer ?

The frequency of the constant-tone [blue line] may not be exactly 8000Hz.
Frequency analysis will show the exact frequency , ( you may have to increase "size" from 512 [default] to 2048 to see the spike ~8KHz ).

[DL Voice]

Thanks for the explanation about the colors. No, I haven't tried a notch filter; I'm not familiar with how to use that yet. I just looked at a recent recording - done under the same conditions as before from what I can tell - and there's no blue line at 8K.

[Trebor]

... I just looked at a recent recording - done under the same conditions as before from what I can tell - and there's no blue line at 8K.

Harmonics of 1kHz, (i.e. 2kHz,3kHz,4kHz ...) , is the characteristic interference emitted by computers (EMI).
Changing the position of the equipment , ( e.g. moving position of mic & power cables ), can make the EMI better or worse, ( like adjusting the antenna on a radio ).

[steve]

No, I haven't tried a notch filter; I'm not familiar with how to use that yet

It's very simple. You just set the notch frequency to the frequency that you want to remove. The "Q" setting is the width of the notch - higher numbers produce a narrower notch (try it with frequency = 8000 and Q = 2)
http://manual.audacityteam.org/man/notch_filter.html