Dolby Noise Reduction

Professional Dolby Noise Reduction

Dolby A noise reduction (NR) was used on millions of 16- and 24-track 2″ multitracks and 2-track masters. It’s a 4-band compander which boosts levels on recording, and compensates on playback, thereby reducing noise

Dolby SR, the successor to Dolby A, offered around 10 dB more noise reduction. Tapes encoded with SR require an SR card for decoding

Domestic Dolby Noise Reduction

Dolby B was a domestic NR commonly used on cassette recorders. In many ways a simplified version of Dolby A, B was s single-band NR system, boosting high frequencies on record and reducing them on playback. As with Dolby A, B required accurate level & frequency response matching for best results. It had the happy by-product of making B-encoded tapes sound brighter on non Dolby-equipped playback systems

Dolby C and Dolby S were later domestic systems

Professional Dolby hardware

Dolby hardware separates the host and NR card. The host typically provides audio input / outputs (via transformers on the 361), power supplies and remote switching whilst the NR card performs audio functions only

Dolby produced hundreds of card types for audio, film, broadcast & etc. In single- and dual-channel models these fell into two main categories, first- & second-generation models.The noise reduction specification (A, SR, etc) remained constant across hardware generations but cards & hosts are not interchangeable between generations as Dolby changed connector standards

First-generation hardware (supports Cat 22 (A) and Cat 280 (SR) cards)

  • 360 – single-channel interface in 1U
  • 361 – single-channel, updated version of the 360
  • 362 – dual-channel in 1U, electronically balanced, front-panel trims
  • 365 – dual channel in 2U, electronically balanced, front-panel trims

Second-generation hardware (supports Cat 350 (SR), Cat 450 (A) and Cat 300 (SR / A) cards

  • 363 – dual-channel in 1U, supports SR & A

For multitrack systems Dolby produced the ubiquitous M16 (16-channel) rack and the later 8-channel expansion. The M16 used standard Cat 22 cards with separate Cat 44H i/o interface cards. The M16 was superceded by the 24-channel XP24 SR rack

 

More info from Sound on Sound

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