In about 1993 Philips, in a joint venture with Bosch (BTS), produced a "BRR" (or Bit Rate Reduction) recording system to enable the full HD signal to be recorded onto a single D1 (or D5 HD) recorder. A low-resolution version of the image could be viewed in the centre of the screen if the tape was replayed on a conventional D1 recorder, and was surrounded by what appeared to be noise, but was in fact simply coded/compressed data, in a similar way to later MPEG digital compression techniques, with a compression rate of 5:1, starting with 72 MHz sampling. Some BRR equipment also contained Quadriga interfaces, for ease of conversion between recording formats, also being switchable between BBC and Philips versions of the Quadriga format. By this time, Quadriga signals were being carried on four SDI cables.