Technical Question about faint “ghost” audio..

A technical question but related to broadcast TV, so I consider this the best place to ask. Obviously, mods, move it if you wish to.

Not so much these days, but in the past, I often noticed an audio “effect” on TV which I’m sure has a simple explanation - hearing a faint “ghost” of the audio soundtrack a few seconds before we were supposed to.

For example, over a silent Granada frontcap, you often faintly heard the opening bars of the Coronation Street theme a couple of seconds or so before it began playing “for real”. The same effect often happened throughout TV programmes themselves with a faint “early” audio track running, and particularly noticeable during quiet scenes.

This often occurred on pre-recorded and home-recorded audio and video cassette tapes too - but it didn’t seem to be restricted to TV shows being played off tape. Adverts or interval music, seemingly played off a disc or cart, often “suffered” from this early “ghost audio” too.

I haven’t explained it very well, but I’m sure older forumers know exactly what I’m referring to. What’s it all about?

Sounds like magnetic transfer between layers of tape as it sits on the roller inside the cassette. If you heard it on other material, chances are it was originated from tape and so the effect was captured during the ingest process. Was always subtle and only noticeable if the imprint was made onto a section of tape with silence or very low level audio.

https://en.wikipedia.org/wiki/Print-through

You get it on a lot of older audio recordings as well.

Thank you. That seems to mostly explain it.

A related question of sorts - what was the reason for (or function of) a faint partial-second of “tone” at the start of an audio recording? Noticeable again on pre-recorded ads read by a announcer/voiceover over a slide (played from a cart machine, I assume), and sometimes heard at the start of music tracks played by presentation.

I have no evidence to back this up, but my guess is it has something to do with a countdown, in the same way a VT clock flashes and beeps at a certain point before the programme starts. I'm welcome to be proven wrong, however.

Cart machines certainly used tones for cueing, on a different track. It's not impossible that there is some cross-talk between the channels?

Audio 'Print-through' on 2 inch Quad tape was an issue. It was indeed a 'pre echo', and on some drama programmes could sometimes almost be spoilers !

Funnily enough i actually first noticed that kind of pre-echo on 'Garth Marengi's Darkplace' where you actually heard a few beats of the theme tune on the Channel 4 logo before the theme actually started. it was actually most likely done deliberately digitally to recreate the effect for people like us to notice It was only after hearing it that i looked up the effect to see why it happened.

This was also a problem on vinyl LPs, not sure if it was called ‘pre-echo’ for that either as Wikipedia suggests it’s a digital-only phrase.

I believe this is the reason why it is recommended to store 1/4" reels with their tails out. This means the print-through will be after rather than before the recording and thus less noticeable.

Many of these slide commercials had their soundtrack recorded on continuous loop NAB cartridges. These had two tracks - one for audio, and a cue track using audio tones to tell the cart when it had come back to the beginning, when it would stop and the audio was thus automatically cued to play again from the start. The same track was also used (with different audio tone frequencies) to provide an autimatic cue to change the slide (if the commercial used several slides) and a final tone to denote the end and put (some) machines into fast forward. These machines weren't perfect and there was often a little bleed from tones on the audio track.

Southern’s “Yeovil Sheepskin shop’ and ‘Bolloms’ the dry cleaners being classic examples of prerecorded slides controlled by the secondary audio tone with voice over on the accompanying main audio track.