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

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

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

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

10. Sine Wave

11. Sine Wave Quantized

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

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

14. 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)

15. Nyquist formula the highest frequency that can be captured in PCM is exactly one half the sample rate f N = (f s /2) where f N is they Nyquist frequency and f s is the sampling frequency

16. Nyquist in Action

17. 44kHz 16 bits 20kHZ target upper limit *2 = 40kHz 10% margin = 44kHz 16bits * 6dB/bit = 96dB of dynamic range

18. 44,000 samples per second 16 bits per sample 2 channels (stereo) 44,000*16*2 = 1,411,200Hz (1.4MHz)

19. Tape Head - Side View

21. “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!

22. Helical Scan

23. 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

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

26. Video monitor showing digital audio being played

28. 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

29. CHAPTER 2: Organizing the data

30. .wav Header data block Header/control track (metadata)

32. binary 1 1 0 0 1 0 1 1 0 0 1 0

33. 1 1 0 0 1 0 1 1 0 0 0 1 0

34. 11001100 10101010

35. LRLRLR or LLLRRR

36. Chapter 3: Error Correction

37. 1 0

38. LRLRLR or LLLRRR

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

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

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

42. Playback challenges 1.Hardware obsolescence - finding a machine is many times more difficult than playing any given tape 2.Fragile Carriers - very old and/or very fragile video formats (typically U-Matic, consumer Beta or VHS) 3.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)

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