Z-systems RDP-1 Digital Preamplifier

This listing is for a very cool Z-Systems RDP-1 digital preamplifier in excellent working condition. Cosmetically a few scraches on top, all lettering is intact, the front face looks very good. Guaranteed to work correctly. Slight surface scratches on top from other gear. Runs on 120-240v auto selection.No remote, can be run from front panel.

The Z-Systems rdp-1 is designed to use digital signal processing to effect changes in the shape of the frequency response without introducing any side effects into the audible signal. It rely's on powerful general-purpose DSP chips, have memory modes for the storage and recovery of settings, and can be operated from their front panels or from their remote controls.

Z-Systems rdp-1: A Professional Tool 
The Z-Systems rdp-1 is a serious tone-bender whose heritage is the recording studio.
Glen Zelniker, President of Z-Systems, has taken the principles of a studio parametric digital EQ and adapted them to work in home systems as a "Transparent Tone Control." In fact, the rdp-1 (Reference Digital Preamp One) is derived from recording/mastering studio devices that Z-Systems has been making for a number of years. Zelniker has developed and incorporated sophisticated DSP algorithms that minimize noise and phase shift even at low frequencies and with large boost/cut settings.

The rdp-1 is a completely digital device without ADC or DAC, basically, and in addition to input selection and gain/balance, the rdp-1 consists of four independent parametric stages and low- and high-frequency shelf controls. The adjustments are not as intuitive as with bass and treble controls; the potential for abuse looms if they are not used with care. On the other hand, the rdp-1's precise adjustments can effectively remaster your recordings.

The rdp-1 uses the industry-standard Crystal Semiconductor CS8412/CS8402 chips and quality Scientific Conversions signal transformers for input/output with up to 24-bit/48kHz precision. (An 88.2/96kHz upgrade is available.) The DSP engine is a 32-bit TI TMS320C31, which does its computations in 40-bit floating-point arithmetic. All front-panel controls are duplicated on the rdp-1's remote handset so that adjustments and mode selections can be made from the preferred listening position.

Placing the rdp-1 into the Input mode permits selection of input source, output resolution/dither, and whether the DSP operates on both channels (Stereo) or on each channel independently (Dual-Mono). Since the output of the DSP is 32 bits wide, the rdp-1 will down-sample the output to a defined bit-width of 16, 20, or 24 bits.

Selection of output resolution and dither will determine whether the full capabilities of the DAC will be realized.
Dither, a calculated (not random) noise signal based on a statistical algorithm, is added during the downsampling from 24 to 20 or 16 bits to avoid the effects of truncation, the visual equivalent of which is the pixelation seen on low-resolution digital images. The rdp-1 offers 24-bit, 20-bit (truncated, no dither), 20-bit (dithered), 16-bit (truncated, no dither) and 16-bit (dithered) outputs.

And don't rely on the advertising, a 20-bit DAC chip is too often mated with a 16-bit S/PDIF receiver (like the Yamaha YM3623) or a 16-bit-input oversampling filter (like the NPC SM5813), and the package is still touted as a 20-bit DAC! Beware: Such devices will lop off anything over the smallest bit limit inside, and actually sound worse than they would with a correctly formed 16-bit signal. The DACs I use are capable of processing 20-bit signals, and they sounded best to me with the 20-bit (dithered) output. The only exception was that the 20-bit (truncated, no dither) form was needed to pass HDCD signals for decoding. Indeed, the rdp-1 passes decodable HDCD in any of its nondithered modes, as indicated by the LEDs on the DACs and by my ears.

Selection of Stereo or Dual-Mono depends on the kind of processing that you intend to perform. Adjustments to low-frequency balance in loudspeakers are often best made in Dual-Mono mode, as such responses are greatly influenced by the unique position of each speaker in the room. On the other hand, adjustments to frequency response to correct anomalies or imperfections in sources are usually best made in Stereo mode, as true stereo recordings carry something of each voice and instrument in both channels. Changing one channel in a way different from the other destroys harmonic and spatial representation. With mono and pan-potted recordings, Dual-Mono mode may be of use.

The Volume mode is an absolute delight: it covers a range from -95db to +12dB, and, in the critical ±12dB span, in exquisitely fine increments of 0.2dB. Increment size increases with decreasing gain, which makes large changes easy where fine control is rarely needed. Aided by my trusty multimeter and a test CD, I could match levels from different sources, eliminating a pesky source of listener bias.
More important, this volume control seems entirely unburdened by the subjective effects of bit truncation, at least in the usable range around unity gain. This is probably due to the high bit-width of the DSP. Raising or lowering the gain by fixed increments (with equivalent analog-domain gain compensation) was an entirely transparent operation to my ears. Even large amounts of attenuation (-20dB to -40dB) were difficult to fault, but the varying noise contributions of the source and analog components made the audible evaluation less than critical. I'm happy to say that, even though the DSP chip is always in the circuit (even in Bypass), inserting the rdp-1 into the system did not compromise the sound in any discernible way.

Actually, I think the system, connected via S/PDIF, sounded better with the rdp-1. At first this bothered me, but it soon began to make sense. I had inserted the rdp-1 into the system between the DDS•Pro transport and the Uther DAC in place of an intervening anti-jitter box (DTI•Pro32 or DragonPro). Bypassing the rdp-1 in that arrangement resulted in a soundstage less stable and deep, and a slight loss of instrument delineation. Zounds! That's the kind of observation often associated with anti-jitter boxes.

Adding in the DTI•Pro32, the presence (or absence) of the rdp-1 was not detectable. My feeling is that, in a low-jitter environment (with the DTI Pro32), the rdp-1 was completely transparent; and that, in a system with some jitter liability (without the DTI•Pro32), the rdp-1 had an ameliorating effect. That's like having your cake and eating it!

The LF and HF shelf controls may have fixed 6dB/octave slopes, but the nominal frequency is variable, as is the magnitude of the boost/cut. (Remember that the slope also determines how far from the hinge frequency the full effect of the boost/cut will occur. A 6dB cut from a frequency of 500Hz will reach -6dB at about 50Hz. A 12dB cut won't achieve that level until about 10Hz!) Consequently, these controls can mimic standard bass and treble controls, but with added flexibility and precision.

It is the four parametric stages that distinguish the rdp-1 from a tone control. One can select center frequency (1/6 octave ISO frequencies from 28Hz to 18kHz), magnitude (from -95dB to +12dB), and bandwidth (Q=0.4 to 8). As Q is increased, the width of the frequency band affected is narrowed and the steepness of the cut/boost increased. Thus, one can attack specific spectral problems with specifically tailored correction and have minimal contamination of the rest of the audible bandwidth. With the four parametric stages and the two shelf controls, the rdp-1 has greater flexibility than octave or half-octave graphic equalizers of fixed, or preset, Q. (Graphic equalizers with 1/3-octave resolution approach this precision.) Moreover, the independence of each stage of the rdp-1 makes it easier to focus on one acoustic problem at a time. The learning curve is steep but short: Use the rdp-1 for a few recordings and you'll develop skill quickly.

The rdp-1 offers a wide range of settings for input source, output mode, and frequency response, and setting these for a particular application takes some time and effort. Fortunately, once you've done this, you can store your preferences as a Preset in any memory location from 1 to 99, for easy recall when needed. Preset 99 is the user-default location and should be programmed to contain the settings you wish to be applied on power-up. Preset 0 is an unmodifiable "flat" stereo setting with 24-bit output. Your choice of any two Presets can be defined as A and B for making rapid comparisons between them. This is particularly useful for comparing an EQ setting against a modification of it as you incrementally approach your optimum EQ setting. In addition, the Bypass mode (filters flat, 24-bit output, no dither) is always accessible for reference. However, the 24-bit output associated with Bypass can create truncation problems with many DACs, so it's best to create your own flat or reference setting with the appropriate output mode.

Remastering Your Recordings 
A few months back an experienced mixing engineer offered to re-equalize any recording submitted by a member of the audience. One of those submitted was a (typically) murky old Doors CD. While listening to the recording, the engineer accessed one of the parametric stages, gave it a boost, and slid it up and down, searching for the voice fundamentals (he knew where they were), then adjusted the gain/Q to make Jim Morrison just a bit more present and live. He followed up by using other parametric stages to re-balance individual instruments. Then, a little tweaking of the HF and LF shelf controls to establish fairly neutral overall response, et voilèa!—the recording sounded new and modern! Not everyone liked the results ("That's not the way the Doors sound!"), but in less than three minutes the recording had been transformed into what the controller/listener wanted it to sound like.

Spec’s

Z-Systems rdp-1 digital preamplifier:
Digital inputs:
2 AES/EBU, 3 S/PDIF (RCA), 1 optical (TosLink with ST-type glass optional).

Digital outputs:
1 AES/EBU, 1 S/PDIF (RCA), 1 optical (TosLink with ST-type glass optional). 24-bit input/output. 32-bit DSP with internal 40-bit floating-point arithmetic, used for all gain and equalization. Dynamic range: >144dB.

THD+N:
better than -135dB.

Number of memories/presets:
99.

Gain control:
from -95dB to +12dB.

Dimensions:
17" W by 4.5" H by 10" D.

Weight:
14 lbs.



Orig Price:
$5000. 


Manufacturer:
Z-Systems Audio Laboratories,

Guaranteed to work correctly for 60 days.

Offered for $1400 w free shipping. It will ship double boxed and carefully packed.

Guaranteed to arrive intact, and to be as described.
 

 Always carefully packed and promptly shipped. 


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