Table of Contents
Introduction
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| Disc | Description |
|---|---|
| Playing time | 74 minutes, 33 seconds maximum |
| Rotation | Counter-clockwise when viewed from readout surface |
| Rotational speed | 1.2-1.4 m/sec. |
| Track pitch | 1.6 µm |
| Diameter | 120 mm |
| Thickness | 1.2 mm |
| Center hole diameter | 15 mm |
| Recording area | 46 - 117 mm |
| Signal area | 50 - 116 mm |
| Material | Any transparent material with 1.55 refraction index. Usually polycarbonate |
| Minimum pit length | 0.833 µm (1.2 m/sec.) to 0.972 µm (1.4 m/sec.) |
| Maximum pit length | 3.05 µm (1.2 m/sec.) to 3.56 µm (1.4 m/sec.) |
| Pit depth | Approximately 0.11 µm |
| Pit width | Approximately 0.5 µm |
| Number of channels | 2 channels (four channel recording possible) |
| Quantization | 16-bit linear quantization |
| Quantizing timing | Concurrent for all channels |
| Sampling frequency | 44.1 kHz |
| Channel bit rate | 4.3218 Mbps |
| Data bit rate | 2.0338 Mbps |
| Data-to-channel bit ratio | 8:17 |
| Error correction code | Cross Interleave Reed-Solomon Code (CIRC) (with 25% redundancy) |
| Modulation system: | EFM |
| Info | ||
|---|---|---|
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Ken C. Pohlmann, The Compact Disc: A Handbook of Theory and Use. Madison, Wisconsin: A-R Editions (1989): 49. |
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| Info | ||
|---|---|---|
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Replication of CDs. Image source: J.M. Eargle. The Compact Disc (CD). In Handbook of Recording Engineering. Boston: Springer (1996): 465. |
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Technical specifications
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| Specification | Description |
|---|---|
| Channels | 2 channel (stereo) |
| Bit-depth | 16-bit |
| Data encoding | Linear PCM |
| Sample rate | 44.1 kHz |
The sample rate of 44.1 kHz was inherited from the widespread practice of using a PCM adaptor to convert digital audio into an analogue video signal for storage on a U-matic videocassette. This was the most economical way of transferring audio from the recording studio to CD manufacturers.CD-DA audio has a bit rate of 1.4 Mbit/s.
Technical specifications for CD-DA are defined in the "Red Book" (IEC standard 60908:1999).
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CD-DA data is addressed on the compact disc using a timecode system of minutes, seconds, and frames, expressed in mm:ss:ff. Timecode frames (i.e., sectors) are the smallest addressable time intervals on a CD-DA and correspond to 1/75th of a second of audio. Timecode frames are distinct from the data frames described above. Each sector can hold 98 data frames, or 2,352 bytes of audio data. The CD is played at 75 timecode frames per second, or 176,400 bytes per second (1,411,200 bit/s). In other words, CD-DA data transfers at a bit rate of 1.4 Mbit/s.
CD-DAs hold more data per sector than CD-ROMs, but the increased storage capacity also introduces a higher error rate. As a result, traditional forensic imaging techniques that involve a single pass over the disc are not suitable for CD-DAs. Instead, software designed for CD-DA extraction is used to convert tracks into standard computer.
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