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): Principles of Digital Audio, Ken Pohlman Resources

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

Sine Wave

Sine Wave Quantized

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

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

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)

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

Nyquist in Action

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

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

Tape Head - Side View

“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!

Helical Scan

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

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

Video monitor showing digital audio being played

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 Audio is clocked at 44,056

CHAPTER 2: Organizing the data

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

binary

LRLRLR or LLLRRR

Chapter 3: Error Correction

1 0

LRLRLR or LLLRRR

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

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

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

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)

George Blood Safe Sound Archive (215)