Some of the blame has to be laid at the execution of the digital output at the CD transport side. The spec calls for an output impedance of 75 ohms and a pulse amplitude of 0.5V p–p. Why anyone would choose an amplitude that low is a sweet mystery of standards committees; a higher amplitude would be far more capable of…
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Digital processing is based on the presence or absence of digital pulses. If we see a pulse, it's a "1"; if we don't, it's a "0." In all our discussions we assume perfect pulses all over the place. Well, the pulses happen not to be that perfect, and with good reason.
The Wadia 2000 Decoding Computer executes over 72 million instructions a second in order to get the required accuracy for the output signal. Resampling at 64x, at a sampling frequency of 44.1kHz, results in 2,820,000 calculated points every second (3,072,000/s for DAT). The Wadia 2000 solves a 12th-order polynomial 44,100 times a second.
Please bear with me as I attempt to simplify some of the more basic concepts. For now, you can take their word for it: when Wadia calls their processor a Decoding Computer, they are not resorting to hype.
I owe many thanks to Donald Wadia Moses…
Wadia chooses to filter the output minimally by slipping a ferrite bead over the DAC output leads for each channel. They feel that the frequency of the residual component is so high that it will be filtered further and eliminated as soon as it reaches the first preamp stage. Don Moses indicated that the effects of more comprehensive filtering could be worse sonically, and chose this minimalistic approach.
The DACs in the Wadia are proprietary 18-bit units, a "transversal, summed-multiport delay-line" design said to have a perfectly rectangular impulse response. The DACs are connected to…
All the connections for the processor appear on the rear panel. Here we find the connector for the fiber-optic cable, the three XLR-type connectors for the power-supply cables—to avoid confusion, these are one each of three-, four-, and five-pin types—and the audio output connectors for the two channels. Tiffany RCA jacks are provided for the single-ended outputs, while three-pin XLRs, wired conventionally with pin 2 "hot," are available for the balanced audio outputs.
The front panel provides display LEDs for indicating the selected sampling frequency, the CPU status—"Standby," "…
The recording that highlighted all of the above was a Philips CD of the Misa Criola with José Carreras. Right from the beginning I could hear the panning of the console gain as the soundspace slowly swelled with ambient residuals. The music commences with introductory drum impacts alternating with stick hits. In the next moment, the whole stage turns into one huge breath intake and the choir starts in with a soft droning hum. At that point the whole stage sprang to life and sang out gloriously. Right in the middle of this setting the voice of José Carreras appeared, anointed with delicacy.…
I was in for more treats when the music started. The organ projected with more power and purity now. The low-frequency growls were just that much more mighty and dynamic; the reedy quality of the upper registers came across with great coherence and freedom.
Let's not forget the space. Now that music was exciting the hall, it was even more obvious we were in a large space, very wide and very deep. My guess at the time pegged it as something larger than a church. Well, lo and behold, Craig Dory confirmed this. The organ happens to be located in a concert hall.
Another direct…
Sidebar 1: Specifications
Description: Stereo digital processor intended to take a standard SPDIF multiplexed L/R, serial digital datastream. Sampling frequencies: 32kHz, 44.1kHz, 48kHz. DigiLink 30 unit converts coaxial digital signal to optical format for feeding the decoding computer. Maximum analog output level: 5V RMS (balanced), 2.5V RMS (unbalanced). Analog output impedance: 3.5 ohms.
Dimensions: 17" W by 2.5" H by 12" D (main unit), 8" by 4.5" by 13.75" (main unit power supply), 8.5" W by 2.5" H by 10" D including psu connector (DigiLink 30), 5" W by 2.75" H by 11" D including…
Sidebar 2: Test System
The following equipment was used to evaluate the Wadia 2000 Decoding Computer. Preamps: Audio Research SP11 Mk.II, Krell KSP-7B. Power amps: two Classé DR-9s, four Krell KMA-160s, each set used in conjunction with the Apogee DAX to power the Apogee Divas. CD transports: Sony CDP-X7ESD, Onkyo Integra DX7500, Teac P-1 CD Drive Unit. For comparison purposes, Stereophile arranged for me to borrow a Theta DSPro processor. All single-ended interconnects and speaker wire were Monster Cable Sigma series, or, in the balanced configuration, Kajelco interconnects, with Krell…
Sidebar 3: Measurements
The first sample of the Wadia 2000 Digital Decoding Computer was bench-tested before shipment to Arnis Balgalvis for review. I measured extraordinarily poor low-level linearity, clearly indicating a malfunctioning unit. When the DAC board was returned to Wadia, they discovered that the linearity adjustments (a small hex-bolt on each DAC) had apparently worked themselves loose in transit. Wadia realigned the DACs and returned the board.
One can verify that the alignment screws are in their factory-set positions by looking at the drop of red sealant on the…
Sidebar 4: JA Measures (& Listens)
Robert Harley describes his experiences with the Wadia 2000 above, during which I was an interested bystander. But when he asked if I could bring my digital-storage oscilloscope to the lab to look at the Wadia's low-level waveforms, I thought of a better plan. "No problem, Bob, send the Wadia 'round to my place and I'll look at it there."
And maybe—heh-heh-heh—do a little listening!
Of course, I didn't have the Teac transport so highly praised by Arnie in his review. But I have to say that when driven by the digital output of the…