John Atkinson

The standalone digital/analog converter emerged as a product category in 1987 with the appearance of the Arcam Black Box and the Marantz CDA-94, closely followed by the PS Audio Link. The idea was that putting the sensitive D/A-conversion and analog stages in a separate enclosure with its own power supply would maximize the sound quality when compared with packing these circuits in the same box as the transport. However, it turned out that the routing of the digital data between transport and processor in the form of an S/PDIF- or AES/EBU-encoded bitstream could introduce word-clock jitterwhich undid much of the sonic advantages. (See "Bits is Bits" by Malcolm Hawksford and Chris Dunn, Stereophile, March 1996.)

"Test We Must," cried High Fidelity's erstwhile editor, Michael Riggs, in a January 1989 leader article condemning the growth of subjective testing. (See the sidebar for Peter Mitchell's obituary of HF magazine, now effectively merged with Stereo Review.) With the exception of loudspeakers, where it is still necessary to listen, he wrote, "laboratory testing (properly done) can tell us pretty much everything we need to know about the performance of a typical piece of electronics...We know what the important characteristics are, how to measure them, and how to interpret the results."

Mytek Digital's Michal Jurewicz (facing camera) was busy all weekend, demonstrating both his company's new Stereo 192-DSD DAC FireWire D/A converter (see "Music in the Round," July 2013) and his 8-channel DSD A/D converter. The latter was being used with an Ampex open-reel recorder just out of shot.

A decade ago, many predicted that amplifiers with switching or class-D output stages would come to dominate high-end audio. In a post–Peak Oil world in which the price of energy would always continue to rise, a class-D amplifier's very high efficiency in converting AC from the wall outlet into speaker-driving power would be a killer benefit. Although a conventional push-pull class-B amplifier has a theoretical efficiency of 78.5%, which would seem usefully high, this efficiency is obtained only at the onset of clipping; the need for the output devices to carry a standing bias current reduces that efficiency considerably, typically to around 50%. Class-A amplifiers are even less efficient, with a maximum of 25%; ie, three times as much power is dissipated by the amplifier as waste heat as is used to drive the loudspeaker (see "Sam's Space" in this issue).