Loud 15.7 kHz tone in movie audio... what is it?

[StickHorsie]

When I run movie audio through a spectrum analyzer (SoundForge), I often see a narrow peak around 15.7 kHz... sometimes it's barely visible, other times it peaks up to 30 dB above the surrounding frequencies - at that point even *I* can hear it, and I know the cat can. (Ears go up, looks disturbed, leaves the room.)

Does anyone know if this is an encoding artefact, something essential for Dolby Surround (like the 19 kHz FM stereo decoder signal) that doesn't get filtered out when you play it at ordinary 2 channel stereo, or something else entirely?

I see it too often for it to be a coincidence, so why is it there?

[Zwitterion]

The line frequency of NTSC is 15750 Hz. You can hear it from your TV, too.
Someone left a TV monitor on during recording.

[StickHorsie]

Ah, so it's nothing essential. :D

I was afraid that if I'd filter it out, friends with fancier PC audio systems than me would suddenly lose signal on 2 of their 7 speakers or something like that.

Thank you! :D

[carlyse_09]

I actually dont know that.Thanks for the information...