- Optical Tracks
- Mono
- variable density vs. variable area
 
- SR
- Dolby A
- magenta vs. cyan vs. black/silver/gray
 
- Mono
- Digital
- SRD / Dolby Digital
- DTS
- SDDS
 
- Magnetic
- Sound on disc
- Silent films
- optical vs. digital vs. mag
- Amplifiers?
- Sound processors
- Speakers