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Hi All

My customer has a digitized audio copy from an old video tape.
I haven't faced this kind of a problem before and cannot find a solution 
to it.

There is a fading in the high frequencies at a rate of about 1,5 to 2 Hz,
the rate is not steady, it varies and it appears only in parts of the 
recording.

The high frequencies have been repeatedly attenuated and attenuation
affects down to 6 kHz at places. There is high frequency content in the
recording up to about 15 kHz.

This sounds very similar to a fading interference that I heard a lot on 
the shortwave
when I was listening to SW bands as a radio amateur. Similar fading 
occurs on
medium and long waves as well. But this recording was not recorded from 
a radio,
it has been copied from a video tape. I don't know if the audio tracks 
have been linear
analog tracks on the tape.

Another way I can try to describe the fading is that you would turn your 
amplifier
gain knob up and down, but the damping would only affect high frequencies.

It is a bit like a longish "dropout" or a fade-out, but the shape of the 
frequencies
in the fade is different to a fade-out in a quarter inch tape.

Does anyone know a way to fix this? I have tried using the Spectral Repair
tool in RX with no success. It is difficult to define such an area, around
which the tool could interpolate stuff into the variably shifting damped 
area.
Also, doing it in smaller pieces doesn't work too well.

There is a screenshot of a four second sample of the spectrogram in my 
dropbox.
https://www.dropbox.com/s/c0n4aojd2w3ou5w/Fading%20screenshot.jpg?dl=0

If anyone is interested to hear a sample of the recording, please email 
me off-list.

Eero
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http://www.tonfiks.fi