Analog versus digital: video and sound
The same shift from a continuous analog signal to a stream of bits that turned CRT television digital also reshaped home video and sound. Below are two comparisons, run the same way as CRT versus digital television.
The VCR versus the DVD player
A VHS VCR records the picture as a continuous, modulated signal on magnetic tape; a spinning head drum writes slanted tracks across it. A DVD player reads pits and lands from a spiral track with a laser beam and rebuilds a digital MPEG-2 stream from them.
| Aspect | Analog | Digital |
|---|---|---|
| Medium | Magnetic tape in a cassette | Polycarbonate optical disc |
| Recording | Continuous magnetisation of tracks | Pits and lands read as bits |
| Pickup | Head drum, slanted (helical) tracks | Laser beam and photodiode |
| Signal | Analog, FM-modulated luminance | Digital MPEG-2 stream |
| Copying | Each copy is worse (generation loss) | Bit-for-bit copy, no loss |
| Access | Sequential, you have to wind | Random, chapters and instant skip |
| Degradation | Gradual: snow, smearing, loss of lock | Abrupt: blocking and stutter, then nothing |
| Resolution | ≈ 240 lines (VHS) | 720 x 576 (PAL) / 720 x 480 (NTSC) |
The turntable versus the CD player
A turntable plays sound mechanically: a stylus vibrates in a vinyl groove whose walls carry a continuous sound wave. A CD player reads optically: a laser reflects off pits, and the bits read back rebuild PCM samples, 16 bits at 44.1 kHz.
| Aspect | Analog | Digital |
|---|---|---|
| Medium | Vinyl record with a groove | CD with pits in a reflective layer |
| Recording | Mechanical groove, walls carry the wave | Pits and lands encoding PCM samples |
| Pickup | A stylus (cartridge) vibrates in the groove | A laser beam reflected to a photodiode |
| Signal | Continuous, analog | Digital: 16 bit, 44.1 kHz |
| Contact | The stylus touches and wears the groove | Contactless optical reading |
| Noise | Clicks, surface hiss, rumble | Silent background, no clicks |
| Access | Sequential along the groove | Random, jump to any track |
| Dynamic range | ≈ 60-70 dB | ≈ 96 dB (16 bit) |
These are conceptual comparisons. Details (formats, codecs, parameters) depend on the specific device and region.