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

                                  
+-----------------------------------------------------------------------------------+
|                               Stereo disc recording                               |
+-----------------------------------------------------------------------------------+



          There are two possibilities to modulate a groove:
                       Simplified presentation

+--------------------------------------------------------------------+
|                                                     |              |
|                                         [vert] [ve] |              |
|                Vertical                   vertical  |              |
|               Modulation                 modulation |Stereo Groove |
|                                             [ve]    |              |
|                                                     |              |
|                                                     |              |
|-----------------------------------------------------+--------------|
|                                                     |              |
|    [vertli1]        verticale         [vertre1]     |   vertical   |
|                     modulation                      |  modulation  |
|                                                     |              |
+--------------------------------------------------------------------+

                                  &

+--------------------------------------------------------------------+
|              Horizontal Modulation               |                 |
|                                                  |   Mono Groove   |
|       [hor]horizontal modulation[ho]             |                 |
|                                                  |                 |
|--------------------------------------------------+-----------------|
|                                                  |                 |
|   [vertli1]       horizontale        [vertre1]   |   horizontal    |
|                    modulation                    |   modulation    |
|                                                  |                 |
+--------------------------------------------------------------------+



                     Both modulations together:


+--------------------------------------------------------------------+
|                                                     |              |
|             Two                                     |              |
|           Channels  [vert]                          |Stereo Groove |
|                                                     |              |
|          [hor]      stereo modulation               |              |
|                                                     |              |
|-----------------------------------------------------+--------------|
|                                                     |              |
|    [vertli1]      both channels       [vertre1]     |  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 45deg                  |
      |                                                       |
      |           [stereoch2] [vert]                          |
      |           [hor]       2 channels, 1 groove            |
      |                                                       |
      +-------------------------------------------------------+



            Each channel half vertical, half horizontal !
                            A compromise


+--------------------------------------------------------------------+
|      Right ChannelCutterhead topCutterhead left      |Right Channel|
|     channelright channalCutterhead right channel     |   Groove    |
|------------------------------------------------------+-------------|
|                                                      |             |
|     [vertli1]      right channel       [vertre1]     |right channel|
|                                                      |             |
+--------------------------------------------------------------------+





+--------------------------------------------------------------------+
|      Left ChannelCutterhead topCutterhead left        |Left Channel|
|     channelleft channelCutterhead right channel       |   Groove   |
|-------------------------------------------------------+------------|
|                                                       |            |
|     [vertli1]       left channel       [vertre1]      |left channel|
|                                                       |            |
+--------------------------------------------------------------------+





+--------------------------------------------------------------------+
|      MonoCutterhead topCutterhead left channelMono       |  Mono   |
|                 Cutterhead right channel                 | Groove  |
|----------------------------------------------------------+---------|
|                                                          |         |
|       [vertli1]           mono           [vertre1]       |  mono   |
|                                                          |         |
+--------------------------------------------------------------------+





+--------------------------------------------------------------------+
|      StereoCutterhead topCutterhead left channel        |  Stereo  |
|             StereoCutterhead right channel              |  Groove  |
|---------------------------------------------------------+----------|
|                                                         |          |
|      [vertli1]          stereo          [vertre1]       |  stereo  |
|                                                         |          |
+--------------------------------------------------------------------+





+--------------------------------------------------------------------+
|                    Maximum Stereo or                     |         |
|              Mono and 1 channel 180deg phased              | Stereo  |
|      Cutterhead topCutterhead left channelExtremest      | Groove  |
|     Stereo: Mono 180  phasedCutterhead right channel     |         |
|----------------------------------------------------------+---------|
|                                                          |mono 180 |
|       [vertli1]     mono 180 phased      [vertre1]       | phased  |
|                                                          |         |
+--------------------------------------------------------------------+



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