early born-digital audio formats
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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Early born-digital audio formats
Compiled by George Blood
• George Blood Audio, LP• Safe Sound Archive
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First Commercially Available Formats
• PCM-1
• PCM-10
• PCM-F1
• PCM1600/1610/1630
• DAT
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“The Dawn of Commerical Digital Recording” Thomas Fine, ARSC Journal (Spring, 2008): 1-17.
Principles of Digital Audio, Ken Pohlman
Resources
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Quantization
• “The process of converting analog signals to digital.” syn: digitization
•Pulse Code Modulation: PCM
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Sine Wave
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Sine Wave Quantized
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PCM≈TIFF
• TIFF congruent to PCM
• DPI congruent to kHZ
• Range of color congruent to range of volume
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Other quantization methods
• PWM: Pulse wide modulation
• Delta-Sigma: sum of change
• Delta-Modulation: change in value (used in SACD’s “direct stream digital”)
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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)
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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 fs is the sampling
frequency
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Nyquist in Action
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44kHz 16 bits
• 20kHZ target upper limit *2 = 40kHz10% margin = 44kHz
• 16bits * 6dB/bit = 96dB of dynamic range
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• 44,000 samples per second16 bits per sample2 channels (stereo)
44,000*16*2 = 1,411,200Hz (1.4MHz)
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Tape Head - Side View
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Tape Head - Side View
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• “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!
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Helical Scan
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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 line25*588*3 = 44,100
NTSC: 30*490*3 = 44,100
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• 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
• white black
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Video monitor showing digital audio being played
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QuickTime™ and aH.264 decompressor
are needed to see this picture.
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• 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
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CHAPTER 2: Organizing the data
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• .wav
• Header
• data block
• Header/control track (metadata)
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binary
1 11 00 10 01 11 00 10 0
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1 11 00 10 01 1 1 0 0 0 1 0
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11001100 10101010
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• LRLRLR or
• LLLRRR
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Chapter 3:Error Correction
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1 0
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• LRLRLR or
• LLLRRR
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Cyclic Redundancy Check Code (CRCC)
• x6+y3+z+1
• assume two values are correct, solve for third: 1+2+3+x=101+2+x+6=10and so on..
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Further reading“Google Search Terms”
• Dual Reed-Solomon [error correction]
• Cyclic redundancy check codes [CRCC]
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• Block structure• Control Track (Metadata)• Interleaving• Error correction• ETF (eight to fourteen transform)• Sync pulses• etc• etc• etc
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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)
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George BloodSafe Sound [email protected](215) 248-2100www.safesoundarchive.com