DAC research

• Published: 2024-10-22 16:49
• Updated: 2024-10-22 17:05

E-mu SP-1200

• Resources
  • Service Manual
  • http://synthark.org/Archive/EmulatorArchive/SP1200.html
• CPU: Z80A, 3.3mHz
• DAC: Sampling and Playback
  • Sampling rate: 26.040hz
  • 12bit, linear encoding
  • Input Anti-aliasing filter:
    • 42dB/Oct (7^th order?)
    • At around 0.85 nyquist?
      • eta: fcutoff​ ≈ 0.85×13.02 Hz ≈ 11.07 Hz
  • Sampling:
    • “Successive approximation” ?
• DAC: Control signals
  • 8 bit, multiplying DAC
    • Triggers the fixed attack/decay envelope
      • Linear, exponential: unknown
      • Attack: ~5ms
      • Controlling the analog SSM2044 filters on channels 1&2
• Zero order hold reconstruction (instead of eg linear interpolation)

Service Manual, p44, figure 7:

Service Manual, p50, figure 8—”Successive approximation:”