Ed's AV Handbook.com
Home Theater & High Fidelity Stereo Audio
Batting practice for the audio/video pro and a primer for the novice
Ed's AV Blog & NEWS
Chap 1 AV Terminology
Chap 2 Physics
Chap 4 Video
Chap 5 AV System Sequence
Chap 6 The Room, Speaker, & TV
Chap 7 Acoustical Strategy
Chap 8 Home Theater by Design
Chap 9 Sales Training
Chap 10 Business & Marketing
- 2 - 3 - 4
The Compact Disc and Digital StorageThe compact disc launced the digital audio revolution in 1982.
CD fabrication begins with the voltage from a microphone or recorded source - analog tape or computer hard disc. The amplitude of the voltage is sampled (looked at and measured) 44,100 times per second by an analog to digital converter. This is referred to as a sampling rate of 44.1KHz.
The sampled voltage is compared to and assigned a value from a predetermined table of 65,536 values. The assigned values are a close approximation of the original voltages. Each value is represented by a 16-bit binary word derived from a numeric 'alphabet' of two numbers (0 & 1) called bits.
The binary word is simply a string of 16 zeros or ones with a total of 65,536 possible permutations. Each bit location in the string represents a percentage of the total possible voltage. Each bit in the string has its particular voltage turned on or off per its instructions: 0 = OFF and 1= ON.
All 16 bits in the ON position equals the total possible voltage.
The 1st bit in the string equals half of the total possible voltage.
The 2nd bit equals half of the 1st.
The 3rd bit equals half of the 2nd.
The 4th bit equals half of the 3rd bitThis pattern continues to the 16th bit.
As an example:
1111111111111111 = total possible voltage
0000000000000000 = 0 volts
1000000000000000 = ½ of the total voltage
0100000000000000 = ¼ of the total voltage
1100000000000000 = ¾ of the total voltage
A micron or micrometer = onemillionth of a meter
The 16 bit data is etched as microscopic pits onto the surface of a compact disc. The pits are impressed onto an injected molded piece of polycarbonate in a 0.5-micron wide spiral track that begins at the center of the disc. The pits are covered in a reflective aluminum layer which is protected by a top acrylic layer.
At playback the disc spins as a laser focuses on the spiral track of pits and the land between the pits which change the reflection of the laser light. An opto-electrical pickup converts the reflected light into an electric current.
A digital to analog converter samples the converted voltage 44.1 thousand time per second and translates the 16-bit code. A sampled change created by a land-to-pit or pit-to-land equals a digital 1 - an ON command. No change per sampled look equals a digital 0 - an OFF command.
The converter reconstructs the 16-bit words and then reproduces their voltages. The converted voltage is finally amplified and delivered to a speaker.
CD is 16-bit code sampled at 44.1K times per second
DVD is 24-bit code at sampled at 96K times per second
DVD-A is 24-bit code sampled at 192K times per second
HD DVD is 24-bit code sampled at 192K stereo or 96K eight channel audio
Blu-Ray is 24-bit code sampled at 192K up to 6 channels, 92K up to 8 channel
|Ed's AV Handbook.com
Batting Practice for the AV Pro and a Primer for the Novice.
Copyright 2007 Txu1-598-288 Revised 2018