Meridian 518 Digital Audio Processor
The 518 is housed in a smart black enclosure identical to that of Meridian's other 500-series components. The circuitry is based on a Motorola DSP-56002 24-bit digital signal processing chip running at 40 or 60MHz (the specs. are unclear here). The selected input signal—there are five inputs and, in Meridian fashion, these have to be assigned to a display alias to become operational—is dejittered using a dual Phase-Locked Loop circuit and a crystal oscillator similar to those in the well-regarded Meridian D/A processors. The reclocked data are then fed to the DSP engine, which performs three main functions, all under the control of front-panel buttons, of other Meridian components via a Comms. socket on the rear, or of a computer via a rear RS-232 port.
I was mostly interested in the 518's resolution enhancement abilities. So, Sherlock, does the 518 do what is claimed for it? Can it give more than 20-bit precision from a datastream limited to 16-bit word lengths?
|Noise Advantage (44.1kHz)|
|(White-spectrum TPDF dither)|
|(Additive, high-pass TPDF dither)|
|(Flat dither, 2nd-order MAF*)|
|(Flat dither, 9th-order MAPÝ)|
|(Flat dither, 9th-order MAF)|
|(High-pass dither, 9th-order MAF)|
|Shape E||Not specified|
|(High-pass dither, 2nd-order MAF)|
Ý MAP = Minimum Audible Pressure, the threshold curve for human listeners using stereo headphones.
All my auditioning of the 518 was done in my usual reference system: Mark Levinson No.31 CD transport feeding a No.30.5 D/A processor via a 1.5m length of Illuminati's excellent new Orchid AES/EBU datalink ($750 [choke, cough, splutter!]). With the Meridian in the chain, a 1.5m length of Madrigal AES/EBU cable took the output of the transport to the 518. The D/A processor was connected to a Levinson No.38S preamplifier via 0.5m lengths of AudioTruth Diamond x2, with then 5m lengths of AudioTruth Lapis or XLO Signature 3.1 feeding a Levinson No.333 power amplifier (review underway) or a Cary CAD-300SEI single-ended amplifier. Loudspeakers were B&W Silver Signatures (mainly), the four pairs of speakers I am currently reviewing—JMlab Micron Carats, Totem MANI-2s, Joseph RM7sis, and PSB Stratus Mini Mk.IIs—or the Epos ES25s that JE reviews in the next issue. The B&Ws were used with their dedicated silver speaker cables, the other speakers with an 8' bi-wired set of Cardas Cross.
Footnote 1: Putting Pioneer's $25/disc price for the blank 60-minute "consumer" CD-R media into perspective—see SS's review of the new PDR-99 elsewhere in this issue—the latest price we paid for 74-minute "professional" blanks was just $7.50! No doubt this is a consequence of RIAA pressure not just on Pioneer, but on all companies offering consumer-oriented digital recorders.