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

Showing 3 responses by restock

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
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!
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.