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Z-Systems RDP-1 Digital Preamp and EQ Print E-mail
Wednesday, 01 July 1998
ImagePrepare yourself to be amazed. The Z-Systems RDP-1 is one of the most revolutionary high end audio products I have ever encountered. Imagine this; the lights are dimmed, you spin one of your favorite CDs, but the sound is less than what you hoped for. What do you do? Change an interconnect, re-bias a tube, write a letter to a tweaky print magazine?

The answer is none of the above. With a snifter of thirty year-old port in one hand and your Z-Systems RDP-1 remote in the other, you may now confidently make your music come to life.

The Details.
The Z-Systems RDP-1 is a $5000 digital preamp and tone control that serves as the control center for even the most high end audio systems. The Z-Systems RDP-1 accepts 6 digital inputs and then places the digital signal on top of a 40 bit - that's right 40 bit - word. From there, you have the option to add up to 4 bands of digital EQ, a digital high and or low pass filer, plus digital volume control.

Z-Systems RDP-1 re-quantities your 16 bit 44.1 digital word into a 40 bit word. With 40 bits of resolution you have the clarity and headroom to augment your music digitally, in ways never before possible. If you own a serious high end DAC (i.e. a Levinson, Krell, Apogee, Spectral, dCS Elgar, Wadia, Theta, etc.) that can accept either 20 or 24 bit words, you are really in business with a Z-Systems RDP-1. The Z-Systems RDP-1 can downconvert your 40 bit digital word to either 16, 20 or 24 bit words as to best feed your digital processor. Thus your Z-Systems RDP-1 is a quick and easy solution to the 24 bit issue in a world where almost every CD you can buy is 16 bit 44.1 MHz.
Musical Magic with the RDP-1.
The RDP-1 has three knobs and an LCD screen that can be hard to get used to if your not familiar with the basics of EQing your audio signal. Do not be alarmed, the Z-Systems RDP-1 is easy to learn how to use. Simply, you are given as many as 4 parameters to set EQ points for which you can raise or lower a frequency as well as decide exactly how narrow or how wide that EQ effects will be in the overall frequency range of the system.

Here is an example of how to use your RDP-1 to make your music really sing:

1. Put in a CD you love, but know sounds boomy in the mid bass. "Sledgehammer" from Peter Gabriel's So record comes to mind.

2. Select number 1 of the 4 EQ parameters on the remote. Use the gain control (it is a +/- adjustment) on the remote to select a frequency of lets say, 63 Hz to add in this case some deep bass. Bump the deep bass up to about +2.4 to 3 dB. Keep the slope adjustment narrowed to 1 for now.

3. Follow the same procedure for the second of the four presets for a mid bass frequency of 120 Hz. In this case set the mid bass parameter to -0.6 or -0.8. Once again, keep the slope to 1 based on how close the two EQ points are.

Rule #1: The number one rule of EQ is you always use your ears as a guide. Only your ears know what is right. Don't worry about what anyone else says, you and only you, know what sounds right.

Rule #2: As you spend more time with an RDP-1 you will find that the best results are attained by adding EQ as if it were a flavorful spice. A little goes a long way.

You will find the results of the above EQ setting to change a `boomy' sounding recording into one with much tighter and more punchy bass. You may consider reserving one of your 100 presets in your Z-System's RDP-1's memory bank for this one.

Taking the sizzle out of the bacon.
Tightening up the bass is only one of the tricks you can perform when you insert the Z-Systems RDP-1 into your system. Hot sounding CDs or bright tweeters can be easily tamed by creating a high frequency EQ point (perhaps 14 kHz) and ever so slightly reducing the frequency. Depending on the bandwidth of the brightness you can also adjust the slope of the parameter from very specific to very wide.

Another method is to insert a low pass filter to gently EQ the high frequency information in the signal path while allowing almost all of the rest of the audio signal to pass untouched.

I use the low pass filer to overcome the ever so slight brightness I find my Wilson Watt Puppy's to have in my room. It only takes -0.2 dB of EQ to cool down my Watts in my room. This solution is a heck of a lot easier getting involved with cable neurosis or replacing electronics.

How does the Z-Systems RDP-1 sound?
Unlike other excellent analog tone controls such as the Cello Audio Palette ($23,500) and the Avalon Design 2055 ($5000), the Z-Systems RDP-1 is a product that has both a digital tone and volume control. I found the RDP-1 to have very little audible flavor, but radically positive effects on the sound of the musical signal.

The RDP-1 is not as warm sounding as the Cello Audio Palette or the Avalon 2055, yet it is very neutral and perhaps even a bit dry in comparison. The Z-Systems on the other hand is not another analog device added to the signal path. My listening test found the RDP-1's dithering to improve the sound of my system even without any EQ. I would surmise that my 20 bit Mark Levinson No. 36s 20 bit DAC was more happy being fed a 20 bit dithered signal than a standard 16 bit signal.

The RDP-1 as a stand alone preamp.
You can use a Z-Systems RDP-1 as a preamp with the addition of a $625, 20 bit analog to digital converter you can take 8 digital and 2 analog inputs into your RDP-1 and switch and attenuate them digitally. Does the RDP-1 sound better as a digital preamp or in addition to an analog preamp? It depends. I have been using a Balanced Audio Technology VK5I preamp in my reference system. With the BAT out of the loop you obviously loose the tube's warmth, but you gain wicked presence. I never found the Z-Systems to be worse than the BAT VK5I, just different. I will likely keep my RDP-1, but I doubt I would sell off my reference Mark Levinson No. 380s preamp or the BAT VK5I. If I had a lesser preamp I would definitely sell it to use the Z-Systems RDP-1 exclusively.

Righting your system's wrongs professionally.
Some music lovers are not interested in playing with EQ for program material, which is a valid opinion. Yet you still need a Z-Systems RDP-1 to get the most from your music system in your room. Music playback systems are imperfect and listening rooms are even worse. Professional acousticains are capable of measuring your room to scientifically ascertain what are your sonic problems. He or she will be able to tell you what kind of room treatments you'll need while at the same time setting a basic EQ to elicit the best from your music playback system. Professional acousticains are used to bring recording studio playback systems up to speed, but rarely is this the case in a music enthusiast's home. Using a Z-System RDP-1 and possibly some tasteful room treatments you can improve your existing system immeasurably.

The Downside
There isn't much here. The three knobs on the faceplate are weird for me to use, thus I only ever use the remote. Unlike adding a new pair of speakers, a DAC or a preamp to your system, there is a learning curve with the RDP-1 is. Considering the advantages a digital EQ brings to the musical equation, the learning curve is well worth it.

It is rare when I encounter a single product that does so much to positively effect the enjoyment of my music. The Z-Systems RDP-1 adds digital volume control, high and low pass filters, 4 adjustable bands of EQ plus the ability to feed your DAC up to a 24 bit, dithered digital word. That is quite a value for $5,000. The RDP-1 is a very competent digital preamp worthy of replacing many mid-level preamps or in conjunction with any ultra high end unit. When you factor in the ability to easily augment your music playback, while the lights are dimmed and your attention is focused on your music, you realize the true power of the RDP-1. It is a product that empowers you to make your music sound the way that you want it to.

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