Comments on: What's the phone-like sound at the end of my video tapes?

Question: What's the phone-like sound at the end of my video tapes?

freddymungo — Mon, 10 Jul 2006 22:11:58 -0800

So I've been watching a bunch of older movies on VHS like Wait Until Dark (1963) and Sword in the Stone (1967). At the end when everything's black, right before it turns to the black and white noise, there's a sound of a phone dialing very quickly, or something similar. Anybody else ever noticed it? Out of curiosity, any ideas on what that is, how it happens, why it's there, or anything at all about it?

By: AllesKlar

AllesKlar — Mon, 10 Jul 2006 22:18:39 -0800

I think what you are referring to is macrovision, an attempt to thwart duplication.

By: cortex

cortex — Mon, 10 Jul 2006 22:20:50 -0800

Is this a quick little series of rising tones? I've noticed the same thing on some cassettes. I presume it's a sort of test-pattern—frequency response of your audio channel can be measured by what portion of the pattern is audible, or such.

By: flabdablet

flabdablet — Mon, 10 Jul 2006 22:50:00 -0800

If it's the same thing I've heard, it's a sequence of tones, about four tones per second, with each tone an octave above the one before. I'm guessing that this is the cue tone referred to about half way down this page.

By: delmoi

delmoi — Tue, 11 Jul 2006 00:01:34 -0800

I have heard it on VHS tapes. It can't be macrovision because it only plays for a few seconds. You could just fast forward past it.

Remember, DTMF tones are very easy for electronic devices to detect, that's why they were used in the phone system (way before computers).

By: delmoi

delmoi — Tue, 11 Jul 2006 01:20:40 -0800

Oh, from here (googling "VHS DTMF")

It's called DTMF signaling. Its information that is put on the master video that tells the automated duplication equipment essential information about what is being recorded. Information ranging from audio levels to the overall time length of the video is encoded into those tones. When the individual recorders receive the tones, it will automatically make the necessary adjustments to ensure the highest quality video possible.

By: neckro23

neckro23 — Tue, 11 Jul 2006 01:50:58 -0800

I've heard similar DTMF tones on mass-produced audio cassette tapes, as well.

By: sohcahtoa

sohcahtoa — Tue, 11 Jul 2006 04:22:17 -0800

When we first got a VCR those tones fascinated me. Thanks for asking.

By: Tuwa

Tuwa — Tue, 11 Jul 2006 05:31:54 -0800

Yes, thanks for asking. I've heard that countless times, kept forgetting to research what it was, and somewhere along the line started taking the tones for granted.

By: freddymungo

freddymungo — Tue, 11 Jul 2006 07:01:52 -0800

It looks like it actually is the sound of a phone dialing; I guess videos apply the same principle to provide different information. Cool how that works; thanks for the answers.

By: Wild_Eep

Wild_Eep — Tue, 11 Jul 2006 07:13:02 -0800

I remember hearing it during cable TV in the 80's. Especially on the Nickelodeon network.

I still hear it on OLN. In fact, I heard it last week.

I suspect it's some kind of signaling tones, but I don't know what they'd be signaling.

By: baylink

baylink — Tue, 11 Jul 2006 08:15:58 -0800

If you're hearing in on a *broadcast*, then it usually *is* DTMF tones, and it's an in-band signal to an early broadcast commercial insertion system to insert local advertising in a break -- we had such an encoder in the rack when I worked at MOR Music TV in the early nineties.

These days, I think they do that in a fashion which isn't audible.

It wasn't *supposed* to be audible *then* -- there was a delay long enough for the DTMF decoder to lock up that was supposed to be put in the audio path, but not all systems were lined up properly.

If the VHS tape was *not* made off-air, I'm not sure what it would be, and if the tones were *not* DTMF tones (which "4 notes each rising an octave" does *not* sound like), they might well be audio line-up tones for checking frequency response on the dubbing rack.

By: ajpresto

ajpresto — Tue, 11 Jul 2006 08:46:21 -0800

I hear DTMF signals (I guess) all the time on CourtTV. Drives me friggin' nuts. Between the show and commercials, it sounds like a phone call, between commercials it's in there sometimes, and then from the commercial to the show. Beep-boop-bop-beep. Ugh.

By: Flashman

Flashman — Tue, 11 Jul 2006 10:51:19 -0800

If it is this:
It's called DTMF signaling. Its information that is put on the master video that tells the automated duplication equipment essential information about what is being recorded. Information ranging from audio levels to the overall time length of the video is encoded into those tones. When the individual recorders receive the tones, it will automatically make the necessary adjustments to ensure the highest quality video possible.

shouldn't it be at the beginning rather than the end of the program being recorded?

By: lockle

lockle — Tue, 11 Jul 2006 11:55:08 -0800

shouldn't it be at the beginning rather than the end of the program being recorded?

Perhaps it's a signal to the recording equipment that tells it that there is no more tape to copy.

By: Steven C. Den Beste

Steven C. Den Beste — Tue, 11 Jul 2006 13:48:20 -0800

I agree that it's an "end" signal. The reason for using a multiple-step DTMF is to minimize the chance of false-positives from the film soundtrack.

By: daisyace

daisyace — Tue, 11 Jul 2006 18:23:08 -0800

One of my very favorite musical artists (ok, he's my brother, but still...) made an instrumental song out of the ones that are on audiotapes. You can listen to it here if you want to see if that's the same thing as a DTMF. (I guess now that people don't grow up hearing these sounds on their tapes, the song's basis is becoming obscure -- makes me feel old!)

By: flabdablet

flabdablet — Wed, 12 Jul 2006 16:49:55 -0800

The tones I was talking about earlier are the ones that daisyace's brother used for his main riff. There seems to be a bit of DTMF back there in the rhythm track too.