What does a vinyl record groove look like?


I have been scouring the internet in an effort to better understand how vinyl is cut and what the groove actually looks like, and therefore tracks like. This is what I think I have learned. A record cutter is a 90 degree V-shaped chisel that undulates back and forth and up and down and in so doing cuts vertical tracks into the sides of the groove it cuts. Bass notes are large undulations (relatively speaking) with midrange and treble undulations riding on top of them and along with them. According to Neil, who might chime in here, the cutter is tilted back 1 degree like a chisel might be, in order to peel up the vinyl that it removes as it cuts. Am I right when I say the cuts in the 90 degree sides of the groove are then 1 degree of vertical (as you look at a groove from the side)? What confuses me is I keep reading articles that talk about 22 degree, or 24 degree, or something like that, cutting angles. What is this all about? My whole purpose here is to completely understand how a groove really looks so I can better understand how a stylus can best track that groove. Not to mention it is flat out amazing to me that all that information can be cut into the groove of a chunk of vinyl in the first place.
240zracer
"Not to mention it is flat out amazing to me that all that information can be cut into the groove of a chunk of vinyl in the first place"
That is an understatement!! It amazes the heck out of me too. Other key question would be which side of the groove is Left channel and which one is Right?
Sorry 240zracer, I don't have answer to your original question.
Am I right when I say the cuts in the 90 degree sides of the groove are then 1 degree of vertical (as you look at a groove from the side)?
Correct, subject to a few refinements:
- different record producers used slightly different angles over the years
- variations from one cutting lathe to the next
- variations from one cutting stylus to the next
- variations from one machine setup person/operator to the next, etc.

What confuses me is I keep reading articles that talk about 22 degree, or 24 degree, or something like that, cutting angles. What is this all about?
The 1 degree angle Neil mentioned and which you have visualized correctly, refers of course to the angle of the edges of the cutting stylus itself (compared to straight vertical). Of course to play a record back most accurately requires that the contact edges of the playback stylus be at the same angle. This ~1 degree angle (cutting or contact edges of styli compared to vertical) is called the Stylus Rake Angle - SRA for short.

That 22/24/etc. degree angle you heard about is the angle of the cantilever when viewed from the side, relative to the horizontal plane of the record. Technically it's the angle between two intersecting lines:
a) the horizontal plane of the record and,
b) a line drawn from the point of the stylus through the pivot point of the cantilever inside the cartridge suspension.

This is called (mysteriously) the Vertical Tracking Angle - VTA for short.

[quote]My whole purpose here is to completely understand how a groove really looks so I can better understand how a stylus can best track that groove.
That is a VERY useful mental exercise. Learning to think like a stylus trying to trace a modulated groove is most helpful. It will save you all kinds of time and trouble when setting up or adjusting your rig (or anyone else's rig for that matter).

The more you listen to vinyl and make adjustments, the more you hear and understand - especially if you work at it. Your ability to hear when something is will improve. Your ability to understand what to adjust, in which direction and by how much is an ear/brain skill. You can develop and improve this skill with practice and reflection.

Go to Vinyl Asylum and read the FAQ's. Most of what's there is correct and all of it is interesting. Jon Risch's article, "VTA once and for all" is especially helpful for understanding the questions you've posed here.

[quote]Not to mention it is flat out amazing to me that all that information can be cut into the groove of a chunk of vinyl in the first place.
Me too!

Don't forget to enjoy the music. That's what it's all about!
Doug
Inner groovewall = L channel
Outer groovewall = R channel

Very important to know for fine-tuning antiskate, for example.
Just a point of clarification:
Only the metal master is 'cut', the actual vinyl lp's are stamped from the metal masters.
This is pretty cool

Go to my system and you can see what a record groove looks like with a needle in it.

Mark
Mark! That is an amazing picture! Probably the best example of a picture being worth a thousand words I have ever seen. Thanks, Doug, I knew I was missing something. I am having a big problem with a defective cartridge right now but I am one of those guys who is right on the verge of some really good analog sound.
Mark02131,
I agree that's an incredible picture. Do you know what magnification was used? What cartridge/stylus?

240zracer,
Sorry for not previewing my post before hitting "submit". Your words and mine got a bit tangled up. I'm waiting for a TT motor repair myself. Between the two of us we almost have a working rig!

Doug
That pic of the stylus in the groove mentioned above is from an Electron Microcsope. Still very cool.
Also, it should be mentioned that the audio signal that is used to 'cut' the tracks on the master is first 'equalized' (the RIAA standard curve) to lower the level of the Bass frequencies, as to not to cut too wide of grooves in the record. When you playback the record, your phono preamp reverses that frequency response curve to restore the low frequencies. This is one reason why you cannot hook your turntables' output jacks to a line-level input on your preamp like you can with a tuner/CD/tape player.
Truly a wonderful picture! Is there any way to get just as good of an orthogonal picture so we can see an example of importance of SRA?
Most of the contributors to this thread will find this info elementary but the sites are good resources and the vinyl groove photos are unique

Micrographia

Westrex Cutting Head & Scully Lathe
Dougdeacon, I thought that the lateral movement of the stylus produced only the mono signal, and the vertical movement gave the signal the stereo balancing. Am I wrong about this?
.bookmark.
.

I thought that the lateral movement of the stylus produced only the mono signal, and the vertical movement gave the signal the stereo balancing. Am I wrong about this?

The first few pages of the Michael Fremer Setup DVD includes a .PDF file that gives an informative accounting of how it works with some nice diagrams.

Rgds,
Tim
Fatparrot,
You're right, but vertical stylus movements are not a result of the groove itself moving up and down. It doesn't. Vertical stylus motions result when a different undulation is cut on one groove wall vs. the other. This differential between the resultant L wall and R wall vertical motion creates L-only or R-only signals.

From the information sheet included with my HFN&RR test record:
On a stereo disc the two groove walls carry related but nevertheless independent signals, each wall undulating at 45 degrees to the record surface. ...

With modulations on one groove wall only... a stylus perched firmly in the groove must move both laterally and vertically.

In stereo recording and reproduction those sounds emanating from the center of the picture are represented by exactly equal signals in the left and right channels, and in accordance with an agreed convention such signals operate the disc cutter so that as one wall goes up the other comes down, resulting in purely lateral groove movement. This of course, is the same as on mono discs, which can be regarded from this point of view as stereo recordings of central sound sources only.

Doug
Great thread and nice responses!

A quick clarification of the stylus motion in a grove: The left/right signal is encoded in +-45 angle plane. Vertical or horizontal motion are additions/subtractions of L and R signal. A good picture of cutting motion is found here:

Stereo disc recording

Therefore vertical or horizontal motion alone do not contain any "stereo" information. Only the combination does. Stated correctly the +45 degree plane contains one channel and -45 degree plane contains the other. Also, check out wikipedia's description:

In the Westrex system, each channel drives the cutting head at a 45 degree angle to the vertical. During playback the combined signal is sensed by a left channel coil mounted diagonally opposite the inner side of the groove, and a right channel coil mounted diagonally opposite the outer side of the groove.

It is helpful to think of the combined stylus motion in terms of the vector sum and difference of the two stereo channels. Effectively, all horizontal stylus motion conveys the L+R sum signal, and vertical stylus motion carries the L-R difference.

Also, its a good exercise to look at a cartridge. The cartridge coils reflect the encoding in the 45 degree plane as well

Sketch of stereo cartridge

I hope this helps picturing vinyl cutting and playback somewhat.

Enjoy!

Rene
To add a bit more accurate information about how grooves get there, it is a lacquer that the cutter head cuts the groove in. Not vinyl or metal as previously mentioned. Then the lacquer (mother) disk is electroplated with silver and nickel to create the basis for a (father) plate stamper that becomes one of the molds for making our records. What I find most amazing is that after all these transfers we still get an amount of information that gives digital a run for its money and IMHO is still sonically superior! Happy Listening
Good comments about the making of vinyl records. A small movie I found helpful that explaings the cutting and pressing process can be found here:

How Vinyl Records Are Made PART 1 OF 2

Enjoy!
Very nice Restock! This should be part of a mandatory audiophile education courses 101 & 102.
Happy Listening(watching)!
Bookmarking this but interesting that Mark's photo of a groove and the one from Micrographia.com are so different (Mark's being jagged, and the Micrographia groove looking so smooth...
One of the best threads EVER!

THANK YOU!!!
I would second your comment T_Bone. Mark's photo looks rather bizzare compared to the micrographia photos. Do you (Mark) have any details on who produced it and how?
I don't remember where I found it. Sorry! It was on a vinyl website somewhere.

Mark
Here is a thought: The difference between the two grooves could be just the difference in the recorded signal in these grooves. The microphonia look like close to only a sine signal while Mark's picture could be featuring a pink noise or dense classical orchestra passage.

Just imagine a graph of your woofer displacement in your loudspeaker vs. time - it would look very jagged in the second case. Also, note higher frequencies are recorded with more amplitude than lower ones on vinyl which will make it look stranger.
Proving once again that a picture's worth a thousand words. Thanks to Mark02131 and Restock for posting those great resources.
What's the difference in pictures... How about the fact that the magnification is miles apart between photographs? Mark's is a close-up with a Electron Microscope and shows the detail within the groove and the stylus and the other is not as close-up, so it just shows the groove?
Happy Listening!