Hi Eero,

It looks like some sort of hi frequency inter-modulation that probably 
happened during the video transfer. I would suggest posting your 
question on the AMIA listserv ([log in to unmask]) where there are alot 
of experts at transferring and archiving content from videotape.

Cheers!

Corey

Corey Bailey Audio Engineering
www.baileyzone.net

On 4/25/2019 9:14 AM, Eero Aro wrote:
> 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
> ----------------------------
> http://www.tonfiks.fi