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Early born-digital audio formats

Early born-digital audio formats. Compiled by George Blood George Blood Audio, LP Safe Sound Archive. First Commercially Available Formats. PCM-1 PCM-10 PCM-F1 PCM1600/1610/1630 DAT. “The Dawn of Commerical Digital Recording” Thomas Fine, ARSC Journal (Spring, 2008): 1-17.

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Early born-digital audio formats

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  1. Early born-digital audio formats Compiled by George Blood • George Blood Audio, LP • Safe Sound Archive

  2. First Commercially Available Formats • PCM-1 • PCM-10 • PCM-F1 • PCM1600/1610/1630 • DAT

  3. “The Dawn of Commerical Digital Recording” Thomas Fine, ARSC Journal (Spring, 2008): 1-17. Resources Principles of Digital Audio, Ken Pohlman

  4. Quantization • “The process of converting analog signals to digital.” syn: digitization • Pulse Code Modulation: PCM

  5. Sine Wave

  6. Sine Wave Quantized

  7. PCM≈TIFF • TIFF congruent to PCM • DPI congruent to kHZ • Range of color congruent to range of volume

  8. Other quantization methods • PWM: Pulse wide modulation • Delta-Sigma: sum of change • Delta-Modulation: change in value (used in SACD’s “direct stream digital”)

  9. 1’s & 0’s • light on light off • positive voltage negative voltage • positive magnetic flux negative magnetic flux • lands (light reflects) pits (light doesn’t reflect)

  10. Nyquist formula • the highest frequency that can be captured in PCM is exactly one half the sample rate fN = (fs/2) where fN is they Nyquist frequency and fsis the sampling frequency

  11. Nyquist in Action

  12. 44kHz 16 bits • 20kHZ target upper limit *2 = 40kHz 10% margin = 44kHz • 16bits * 6dB/bit = 96dB of dynamic range

  13. 44,000 samples per second 16 bits per sample 2 channels (stereo) 44,000*16*2 = 1,411,200Hz (1.4MHz)

  14. Tape Head - Side View

  15. Tape Head - Side View

  16. “How can we increase the size/length of the signal relative to the head gap?” - We could move the tape faster. - Or we could move the head in relation to the tape!

  17. Helical Scan

  18. How 44,000 became 44,100 • First video recorders used were PAL (European) format • Frame rate is 25 (instead of 30 for NTSC) • Lines per frame is 625 (instead of 525 for NTSC) • 37 lines reserved for sync, overhead, headers • 588 active lines for audio data • 3 samples per line 25*588*3 = 44,100 NTSC: 30*490*3 = 44,100

  19. 1’s & 0’s • light on light off • positive voltage negative voltage • positive magnetic flux negative magnetic flux • lands (light reflects) pits (light doesn’t reflect • white black

  20. Video monitor showing digital audio being played

  21. Color video doesn’t run exactly 30 frames/sec. • 29.97 frames/sec • NSTC Color: 29.97*490*3 = 44,056 • 44,100 comes out of the A to D converter • Video is locked to the incoming signal • Video is played back by the internal crystal running at 29.97 • Audio is clocked at 44,056

  22. CHAPTER 2: Organizing the data

  23. .wav • Header • data block • Header/control track (metadata)

  24. binary • 1 1 0 0 1 0 0 1 1 1 0 0 1 0 0

  25. 1 1 • 0 0 1 0 0 • 1 1 0 0 0 1 0

  26. 11001100 10101010

  27. LRLRLR or • LLLRRR

  28. Chapter 3:Error Correction

  29. 1 0

  30. LRLRLR or • LLLRRR

  31. Cyclic Redundancy Check Code (CRCC) • x6+y3+z+1 • assume two values are correct, solve for third: 1+2+3+x=10 1+2+x+6=10 and so on..

  32. Further reading “Google Search Terms” • Dual Reed-Solomon [error correction] • Cyclic redundancy check codes [CRCC]

  33. Block structure • Control Track (Metadata) • Interleaving • Error correction • ETF (eight to fourteen transform) • Sync pulses • etc • etc • etc

  34. Playback challenges 1. Hardware obsolescence - finding a machine is many times more difficult than playing any given tape • Fragile Carriers - very old and/or very fragile video formats (typically U-Matic, consumer Beta or VHS) • Experienced operators - many apparently catastrophic playback problems are due to simple, easily corrected causes 4. Marriage to video carriers mean you get all of video’s problems too - drop outs (drop out compensation makes matters worse) - time base errors (slow tape speed vs. high frequency) - tracking errors (fuzzy 1s and 0s, including error correction data) - media deterioration (such as Sticky Shed Syndrome)

  35. George Blood Safe Sound Archive georgeblood@safesoundarchive.com (215) 248-2100 www.safesoundarchive.com

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