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BuzzzFuzzz

The Needle in the Groove

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Hey Guys.

 

Rather than googling an audio question, I tend to post here first 'cos I love this forum.

 

I always thought that the left and right channel of phono output came from the two sides of the record groove.  Seems to be logical.

 

My brother was visiting recently and he's a bit of an information and technical guru who has built his own computers and valve, guitar amps, among many other goodies.

He told me that the one channel comes from the sides of the groove, and the other comes from the bottom of the groove.

 

Any insights here?

 

Ant.

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I just had a 'quick' look on Vinyl Engine.  Seems my bro is wrong.  A stylus will only touch the bottom of the groove when it is worn or damaged.

Will look into it further.

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The groove walls are cut in a 90 degree 'V' shape. One side of the V contains the left channel and the other side the right channel.

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A quote from Vinyl Engine...

 

  "kuan: Well, I guess you could easily imagine an arrangement with one channel inscribed laterally and the other vertically and one needle reading both at the same time, but feeding two sensors for the two planes (up/down, left/right). Problem with that would be mono to stereo compatibility. Hence the clever trick was to rotate the whole affair by 45 °, so that the two planes are now left&down/right&up and vice versa right&down/left&up. Now you just need to change the sensor arrangement accordingly, the rest remains the same - and thus you get a solution that is stereo capable and mono compatible at the same time."

 

My bro is sort of correct, there are lateral and vertical readings.

 

I'm still a little confused, can anyone explain it simply and comprehensively???
 

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Stereo records have a 45/45 degree configured groove (kinda like a V), so stereo playback requires lateral, rather than vertical, movement. Each side of the V groove corresponding to one channel - left and right of the stereo content.

 

78rpm records use a mono stylus/needle that reads the mono information vertically.

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17 minutes ago, BuzzzFuzzz said:

My bro is sort of correct, there are lateral and vertical readings.

Yes, but they are old mono recordings.  All modern records are 45/45, one channel per groove side..

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15 minutes ago, BuzzzFuzzz said:

I'm still a little confused, can anyone explain it simply and comprehensively???
 

 

@davm already has!  The groove walls are cut in a 90 degree 'V' shape. One side of the V (the inner side) contains the left channel and the other side (the outer side), the right channel.

 

15 minutes ago, BuzzzFuzzz said:

My bro is sort of correct, there are lateral and vertical readings.

 

 

Not really!  The music comes from the horizontal wiggles in the sides of the grooves.

 

Andy

 

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Copied from a link provided on Vinyl Engine...

 

http://www.vinylrecorder.com/stereo.html

 

There are two possibilities to modulate a groove:
Simplified presentation

 


Vertical
Modulation

vert.gif vertli.gifvertical modulationvertre.gif

 
Stereo Groove
 
vertli1.gif verticale modulation vertre1.gif
vertical modulation

 

Horizontal Modulation
 
hor.gifhorizontal modulationhorre.gif
Mono Groove
 
vertli1.gif horizontale modulation vertre1.gif
horizontal modulation


Both modulations together:
 

 
Two
Channels

 
vert.gif
hor.gif stereo modulation
Stereo Groove
 
vertli1.gif both channels vertre1.gif
2 channels


But:
Horizontal modulation is better than vertical !

Vertical modulation:

More distortion !
Large amplitudes, not possible !


One channel always would be better !

 

The compromise:    

 


All gets turned 45°
 
stereoch2.gif vert.gif
hor.gif 2 channels, 1 groove




Each channel half vertical, half horizontal !
A compromise

 

Right ChannelCutterhead topCutterhead left channelright channalCutterhead right channel
Right Channel Groove
 
vertli1.gif right channel vertre1.gif
right channel

 

 

Left ChannelCutterhead topCutterhead left channelleft channelCutterhead right channel
Left Channel Groove
 
vertli1.gif left channel vertre1.gif
left channel





 

MonoCutterhead topCutterhead left channelMonoCutterhead right channel
Mono Groove
 
vertli1.gif mono vertre1.gif
mono





 

StereoCutterhead topCutterhead left channelStereoCutterhead right channel
Stereo Groove
 
vertli1.gif stereo vertre1.gif
stereo





 

Maximum Stereo or
Mono and 1 channel 180° phased

Cutterhead topCutterhead left channelExtremest Stereo: Mono 180° phasedCutterhead right channel
Stereo Groove
 
vertli1.gif mono 180 phased vertre1.gif
mono 180 phased

 

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No-one has really done vertical modulation since the old mono Edison gramophone  discs.

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