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Sound leakages before the track starts playing

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Sound leakages before the track starts playing

Postby tuttifruti » 12 Oct 2017 01:00

On some records, when the cartridge drops to the lead-in groove, I can hear the 'phantom' split second opening sounds, which are quiet but still audible. After that, the music starts in full volume. I'm not sure what's causing this 'sneak preview' playback? Is it the worn out grooves? Or is it some pressing anomaly?
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Re: Sound leakages before the track starts playing

Postby audiopile » 12 Oct 2017 03:54

This is one of the issues that a disc cutting engineer has to deal with - if the material "between " grooves isn't thick enough - you'll hear the groove on the other side of the hill as pre-echo. What's sorta weird about this is that this becomes more audible and obvious as you improve your arm and cart. Most modern pressings have the cutter head controlled digitally and avoid this isssue -along with a number of other issues related to human error in runnin the lathe . Interesting question - so why do so many of those classic LP's wholly controlled by a human still sound better than anything the machine has done ?
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Re: Sound leakages before the track starts playing

Postby RockerFrank » 12 Oct 2017 12:15

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Re: Sound leakages before the track starts playing

Postby Slavikcc » 12 Oct 2017 14:01

This generally happens on records that was lacquer cut. Albums cut via DMM (Direct Metal Master) are not affected by pre-echo.
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Re: Sound leakages before the track starts playing

Postby audiopile » 12 Oct 2017 16:16

Not diputing this - but what about DMM's would avoid this problem or is this simply because all DMM are cut using digital margin control and avoid this minor issue ? BTW- on classical music with extremely wide dynamic range - this can happen when you have a very quiet solo moment right ahead of a crescendo -annoying.
Last edited by audiopile on 12 Oct 2017 16:28, edited 1 time in total.
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Re: Sound leakages before the track starts playing

Postby Slavikcc » 12 Oct 2017 16:22

I'm guessing this depends on the music itself (for example, music with a lot of bass works best on lacquer) and the label's preference to lacquer versus DMM, which the former costs more there are additional steps involved in making a record cut.
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Re: Sound leakages before the track starts playing

Postby billshurv » 12 Oct 2017 16:39

One of the causes is that the lacquer can deform as it's soft, whereas Copper, being of somewhat stiffer stuff (although soft for a metal). In theory you can cut DMM grooves closer without pre-echo, but in practice things are never that simple!

Of course the pre-echo might have been on the original tape. Did happen.
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Re: Sound leakages before the track starts playing

Postby analogaudio » 12 Oct 2017 19:18

There are two causes for this, one of them is mechanical in nature, as has been described above, the modulation of the cutting stylus is able to slightly distort the wall of the adjacent groove, this can produce a faint audible signal that is synchronized to the revolutions of the disc.

However the more common cause of this "pre-echo" arises from the use of analogue tape in the preparation of the master recording for the cutting lathe. There is a phenomenon peculiar to analogue magnetic tape known as "print-through" whereby the magnetic signal impresses itself through the thin backing layer of the tape into the magnetic material of the adjacent layer. The print-through is very faint however it is audible when silence is followed by a loud section, as at the beginning of the disc, and at the start of each track. This print-through is synchronized to the revolutions of the reels of magnetic tape and usually not synchronized to the revolutions of the LP disc.

Print-through can become stronger over time, and at elevated temperatures, it is present all the way through the music, however is only noticed when there is silence followed by music. This can be prevented by the careful use of non-magnetic leader tape in the preparation of the master recording.

Print-through does not occur with the use of digital tape recording.
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Re: Sound leakages before the track starts playing

Postby analogaudio » 13 Oct 2017 18:37

PS the last part, about print-through increasing, applies to the original analogue magnetic tape recording and does not apply to the LP.
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Re: Sound leakages before the track starts playing

Postby philbrown » 21 Oct 2017 21:58

OK, folks, here goes.
This is called pre and post echo. It's caused by adjacent grooves imprinting on each other. The reason is that lacquer is a plastic medium. It's prevented by opening the pitch up at the beginning and end of the track. It is not electronic so analog or digital program doesn't matter and digital control of the lathe doesn't matter either. We have had digital control of lathes since the mid 70s, first with the Zuma system and then Capps VP and the CBS Compudisc.
If you look at a disc you will see-at least on everything I cut and everything I've ever seen cut-that two or three grooves on either side of a spread are further apart. This is to prevent or minimize pre echo. Pre echo can also occur during program when a loud passage follows a soft one, like the cannon in the 1812 Overture.
Print through is an entirely different matter and was largely eliminated by back coating on the tape.
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Re: Sound leakages before the track starts playing

Postby eddie edirol » 22 Oct 2017 00:02

I know for sure I have an original issue 45 if Hush by Deep Purple which was done all analog. In the lead in groove you can hear the “pre echo” because of what I thought was print through. But maybe now I have to worry about this groove thing? Now I have to play the record again and see if the spot that the label lines up with on the echo is the same spot when the first hit comes in. Haven’t heard this on any of my other records though.
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Re: Sound leakages before the track starts playing

Postby philbrown » 22 Oct 2017 01:58

eddie edirol wrote:I know for sure I have an original issue 45 if Hush by Deep Purple which was done all analog. In the lead in groove you can hear the “pre echo” because of what I thought was print through. But maybe now I have to worry about this groove thing? Now I have to play the record again and see if the spot that the label lines up with on the echo is the same spot when the first hit comes in. Haven’t heard this on any of my other records though.


I can state with 99.9% accuracy that is's pre echo-45s were cut at a higher level than LPs-and it's nothing to worry about.
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