Space / Time Control

Pitch Calibration Manual
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Preface

The goal of pitch calibration is to align the pitch signal sent by the software with the actual movement of the carriage lead screw.

Any offset between the pitch signal and the resulting pitch on the disk is too small to measure directly from a groove. The best approach is to drive the carriage at a constant pitch for several hundred revolutions and measure the cumulative error.

This calibration takes some time but is semiautomated, so you don't need to be present throughout the process.

During these tests, no groove is cut and no audio is sent to the head. The procedure is only meant to move the carriage.
Read and follow the instructions below carefully. If unsure about a step, please contact our support team. The signals sent to the system during the calibration procedure can potentially damage your equipment. You will perform all calibration steps at your own risk.

Prerequisites

None.

Abbreviations

SDMS
Sillitoe Disk Mastering System hardware
STC
Space / Time Control software

References

STC Lathe Calibration Dialog
STC Lathe Calibration Dialog
SDMS Master Control and Space / Time Control Hardware Modules
SDMS Master Control and Space / Time Control Hardware Modules
All alphabetical and numerical references in this manual refer to the images above.

Calibration Procedure

Travel Distance Calibration

Prepare STC and SDMS:

  1. Launch STC and open the Lathe Calibration dialog
  2. Confirm your SDMS Master Control and Space / Time Control hardware modules are connected 7
  3. Select PITCH CALIBRATION 1 in the SOURCE section and set REVOLUTIONS 3 to 200 rev
  4. Reset PITCH OFFSET 4 to 0 µm and PITCH FACTOR 5 to 1.00
  5. Disable automation for DEPTH H, CARRIAGE L, and HEAD P (LED buttons OFF)

Repeat the following steps for each pitch value in the table below:

  1. Disable CARRIAGE L automation (LED button OFF)
  2. Use the XISOX N switch to move the carriage to the 300 mm mark on the RIAA DISK DIAMETER scale as precisely as possible
  3. Enable CARRIAGE L automation (LED button ON)
  4. Set the PITCH 2 control to the next pitch value in the table
  5. Press REC 6 to start the calibration procedure
  6. Observe as the carriage moves and the timer counts down from 06:00.000
  7. After the test completes, note the diameter where the carriage stops (or take a picture)
Pitch Calibration Test Results
PITCH # REV START Ø STOP Ø
100 µm 200 300 mm
150 µm 200 300 mm
200 µm 200 300 mm
250 µm 200 300 mm
300 µm 200 300 mm

Once all tests are complete, send the results to calibration@spacetimecontrol.com for evaluation of your PITCH FACTOR and PITCH OFFSET parameters.

If you are already familiar with the pitch calibration procedure, you can also enter your results into the Pitch Calibration Utility and find the optimized values for PITCH FACTOR and PITCH OFFSET yourself.

Pitch Calibration Project

To fine-tune your pitch calibration, use the Pitch Calibration Project, an 18-minute test program containing noise with strong low-frequency modulation. This program generates a variable pitch signal representative of typical music cuts.

You can download the Pitch Calibration groove file here (20 MB).

Ensure the head is muted during this test. The noise contained in this project is not meant for cutting and can damage your head.
The RIAA DISK DIAMETER scale has three marks for each disk diameter: Ø (DIAMETER), START, and PROGRAM. Whenever you cut a full side with STC, make sure to position the carriage at the START mark for the diameter of the disk. This is the correct diameter to begin the lead in groove.
Pitch Calibration Project

Running the Pitch Calibration Project

  1. Launch STC and open the project Pitch Calibration.groove
  2. Adjust the GAIN control in STC until the program uses 83% disk capacity; leave all other settings at their defaults
  3. Disable automation for DEPTH H, CARRIAGE L, and HEAD P (LED buttons OFF)
  4. Ensure the head is muted G
  5. Use the XISOX N switch to move the carriage to the 12" START position at 298 mm
  6. Enable CARRIAGE L automation (LED button ON)
  7. Ensure the carriage direction switch M is set to F(orward)
  8. Open the Cut Project dialog in STC and press REC to start the test run
  9. After the test is complete, the carriage will stop at the lock groove position
  10. If the pitch calibration is correct, the carriage should stop within ±1 mm of the 12" LOCK mark (Ø 106.4 mm) on the RIAA DISK DIAMETER scale

Fine-Tuning the Pitch Offset

If the carriage stop position deviates by more than ±1 mm, adjust the PITCH OFFSET 4 in the Lathe Calibration dialog:

To calculate the adjustment, use the following formula:

Pitch Offset Delta = (Measured Lock Groove Diameter − 106.4 mm) / 1.22

Measured Lock Groove Diameter = 100 mm

Pitch Offset Delta = (100 mm − 106.4 mm) / 1.22 = −5 µm

You can also use this fine-tuning procedure with any of your own groove projects; the lock groove position should always be identical regardless of the audio content of the program.

Troubleshooting

If you experience variations in the stop-groove position in your cuts, double-check these parameters:

Whenever you make changes to the pitch motor hardware (belt, pulleys, etc.), it is recommended to check the pitch calibration again.