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15.6kHz interference tone

 
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h_taylor
audio school


Joined: 12 Sep 2016
Posts: 1

PostPosted: Mon Sep 12, 2016 11:30 am    Post subject: 15.6kHz interference tone Reply with quote

Hello all,

Not sure if this is in the right place, so sorry if not.

I am studying for a Masters in Acoustics and I am currently researching the presence of a 15625Hz tone (15750Hz in the USA) that I have observed in many mid-90s / early-2000s recordings. It is undocumented in academic literature and I am trying to find out why this is.

I have observed a spike of as much as 16dB above the average 1/3 octave-band level (14130Hz to 17780Hz being the band in question). Following a sample of various recordings from the 90s/00s, I found that the interference tone was more prevalent in music recorded or mixed in certain studios. Albums recorded in Abbey Road in particular seemed susceptible to this interference.

The most likely source of this interference is the flyback transformer in CRT screens being picked up by microphones. I believe this is where recordings have been made in a control room where CRTs are present, or using a desk that had a CRT built in. Indeed, sometimes I can hear it fading in or out with vocal takes, probably where a performance has been punched in next to the desk.

It appears that recordings can also pick up this interference during mixing. To take "The Bends" by Radiohead as an example, the album was recorded in the UK; however, a lot of the album displays the frequency corresponding to the NTSC standard (15750Hz). Sure enough, the album was (re)mixed in the USA.

My question is whether anyone has encountered this interference (in listening or as an engineer). For me as a listener, this sound is very off-putting; there are a few albums I am unable to listen to due to it. If nothing else, I feel like the presence of this tone should be paid attention to when carrying out the inevitable next round of "remasters"...

Thanks,

Harry
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Scodiddly
ghost haunting audio students


Joined: 10 Dec 2003
Posts: 3374
Location: Mundelein, IL, USA

PostPosted: Sun Sep 18, 2016 7:35 pm    Post subject: Re: 15.6kHz interference tone Reply with quote

I can't speak from recording experience, but you're almost certainly right about it being a CRT flyback. I can remember being able to hear that nasty whine while most people couldn't, and I got some very confused looks when I'd start smacking somebody else's CRT in the computer lab.
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Nick Sevilla
speech impediment


Joined: 03 Mar 2008
Posts: 4453
Location: Los Angeles California USA

PostPosted: Mon Sep 19, 2016 2:00 pm    Post subject: Re: 15.6kHz interference tone Reply with quote

I've encountered it only a few times, years ago.

During the time, we would do retakes, and not use whatever monitor as close to the recording equipment as it was.

Permanently solved it by going to LCD displays.
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vvv
zen recordist


Joined: 13 May 2003
Posts: 7977
Location: Chi

PostPosted: Mon Sep 19, 2016 2:52 pm    Post subject: Re: 15.6kHz interference tone Reply with quote

I'm thinking of calling my next band, "15750Hz Hum".

Altho' it's not really a "hum", izzit?

Ah well, confusion to the punters!

Twisted Evil
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digitaldrummer
deaf.


Joined: 24 Nov 2005
Posts: 1972
Location: Austin, Texas

PostPosted: Mon Sep 19, 2016 3:19 pm    Post subject: Re: 15.6kHz interference tone Reply with quote

you know why it hums?

because it doesn't know the words!
Embarassed
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