VMS80 : Mono for Stereo depth control

[johnoisamanc]

Hi All,

I am a trainee cutting engineer & being taught on a VMS-80. The other day I was introduced to the concept of the 'mono for stereo' switch the pitch computer control panel. My mind is farting all over the place.

Could someone give me a simple nuts and bolts understanding of this? My previous understanding regarding 'stereo mode' is that a varying depth is determined by changes in phase & level. So the depth will increase whenever the groove becomes effectively awkward to track on playback. For example an out of phase, loud signal would require the most groove depth, any depth decision would be made between those two attributes.

(as a side note: can a stereo groove crash between it's left and right signal?)

So assuming i'm ok with my thinking on that, mono for stereo disregards phase (vertical) attributes and increases outside of the minimum depth with lateral level changes alone? Whats the reason behind this and when would you gauge this as an acceptable method? It's my understanding this helps you cut louder? how?

I have a feeling this is more simple then i've made it out in my head. Would really appreciate some clarification from more experienced cutting engineers.

[Phinster]

All this does is give you more depth(which is adjustable) when cutting a mono signal.

Mono doesn't give you much increased depth on an 80. ie if you have a 2 thou basic, it tends to stay around there regardless

of signal level. 'mono depth' will treat the mono preview as a pseudo stereo signal and deepen the groove automatically.

Its a convenience really, I can't say I've ever used it much. I cut lots of mono 7 in and use a 4 to 4.5 thou basic, so thats

deep enough anyway. I hope thats a bit more understandable.

[johnoisamanc]

Cheers Phinster

That does help thanks.

Depth control is maintaining a minium depth as stereo content will naturally widen/narrow the groove. So if the signal is mono the minimum depth wouldn't change only the land as amplitude increases. Would you agree that's an accurate assertion?

The mono switch deepens the mono signal groove by swapping phase for amplitude? meaning you can maintain minimum depth while cutting louder. You'd need more depth with loudness to hold the stylus in during playback? You would also have the ability of maximising space over setting a larger minimum depth? Is this right?

We were actually cutting a stereo track, with a fair amount of difference information (we also had the EE in). So i'm struggling to see why it was used in this situation. If you had content which had a little stereo I could see that this switch might help you cut a bit louder. Can anyone confirm this?

[Phinster]

Your assertions are correct. If you use mono depth while cutting in stereo, the opposite tends to happen.

If you have the module with the land economy, vertical and lateral offset controls on it, you can use this with a stereo signal

to increase or decrease the dynamics of the pitch/depth computer. Sometimes if a signal is heavily compressed, you can

waste land space, so using the lateral offset helps. The land economy control (marked o a b c ) influences the amount

of ' groove snuggling' ( a Neumann term btw!) Position c being max. land economy without over cutting .This is what the VMS

80 is all about!

[johnoisamanc]

The land economy control (marked o a b c ). No don't seem to have this on the 80 i'm using. Isn't packing grooves tight the whole point of a preview comp on any lathe??

I've also noticed another feature i've never used and that's 'secondary depth'. It doesn't move in relation to the 'primary' depth setting. I wonder what that's for?

The mono for stereo has a potentiometer marked 0 to 0-10. I'm guessing that is a maxium depth setting?

[Dub Bull]

Maybe the "Secondary Depth" you have is for "Increased Depth during banding, lead in, and Finish?" This was customary in the past. It is easier to drop the needle manually where the groove width is greater. Of course, by increasing the depth, we are also increasing the width (by twice the depth increase if doing microgrooves and by even more when using a 110-degree included angle for coarse groove cuts). Not that it's germane, but I don't even like the speed of 45 rpm records, and I really don't like the speed of the "78" rpms. Why? Because it increases the friction, wear, and tear while simultaneously stealing available time. Yes, it's all in the interest of better fidelity, but 33 1/3 sounds fine if the tape is good! 16 2/3 for speech and 33 1/3 for music - from now on!

Berliner-spec one-sided 5-in pressings should still be available for toy records, too!

Solidarnos'c',
Father Jose'