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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
dougdeacon
3,338 posts
 
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
restock
831 posts
 
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
r_f_sayles's avatar
r_f_sayles
872 posts
 
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
restock
831 posts
 
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!
r_f_sayles's avatar
r_f_sayles
872 posts
 
Very nice Restock! This should be part of a mandatory audiophile education courses 101 & 102.
Happy Listening(watching)!
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