CEDAR DCX, CRX, and DHX Digital Audio Restoration Modules

by Dr. Frederick J. Bashour

My word! That CEDAR audio restoration equipment just gets friendlier and friendlier. I've just spent an extremely enjoyable week using three CEDAR digital audio restoration modules: the DCX declicker, the CRX decrackler, and the DHX dehisser. I produced exceptional results from all three of them without much muss and fuss at all.

 
Product Points
 

CEDAR Audio Restoration Modules

Applications: Audio restoration of LPs, tapes and other noisy program material

Key Features: 40-bit floating point DSP processor; single- or dual-knob adjustment

Price: DCX - $5,995; CRX: - $6,495; DHX - $6,875

Contact: CEDAR Audio USA at 207-828-0024.

Product Points

Plus

Easy to produce outstanding results

Easy to learn to hear processing artifacts and to readjust controls to eliminate them

Hardware configuration more stable than competitive software solutions

Minus

Expensive

The Score: If you do any restoration work at all, you must hear these new CEDAR gadgets.

I dare say the time isn't far off when this technology will trickle down to the world of home audio and anyone with a significant collection of old-fashioned tapes and LPs will consider CEDAR equipment a must-buy. Although for the moment it remains in the professional domain, it's so easy to use that just about the only thing preventing consumers from enjoying its benefits is the price.

Features

The DCX declicker ($5,995) removes a wide range of clicks, scratches and other impulse degradations. The CRX decrackler ($6,495) is designed to remove crackles such as fine vinyl surface noise. It also removes buzzes and many types of distortion. The DHX dehisser ($6,875) is used to reduce broadband noise, such as tape hiss and analog mixer noise.

The three CEDAR units have a uniform look. Each is a single-rack-space unit, finished in tasteful black, with a power/standby toggle switch on the left. The rest of the front panel features three push-buttons - each associated with a pair of green LEDs, and one, two or three adjustment pots - the only front panel feature one could actually use to distinguish between the units from across the room.

The three push-buttons select AES/EBU or S/PDIF input, unity gain or -3 dB gain, and I/O for the particular process involved. A pair of LEDs on the far right side of the front panel indicates whether the unit is in standby mode or fully powered up. It is interesting to note that as soon as the units are plugged into AC they immediately go into standby mode - only complete removal of AC completely shuts them down.

The rear panels are identically configured. As the units operate solely in the digital domain, only digital I/O is provided. Both AES/EBU on XLRs and S/PDIF on RCA connectors are available. An I/O of 24 bits is implemented and verified by observation on bitscope. The particular input connector desired must be selected on the front panel, but both outputs are simultaneously available. The ubiquitous IEC power connector completes the rear panel; the power supply can be connected to, and will automatically adjust to, any voltage worldwide.

In use

I set the units up in a series digital configuration. As suggested in the CEDAR manual, I set up the declicker first in the chain, feeding the decrackler, which, in turn, fed the dehisser. I connected a 24-bit AES/EBU output from my Apogee Electronics AD-8000 (PAR, 11/98, p. 18) to the declicker's appropriate XLR connector, and returned the digital output from the dehisser to a position in my digital switcher. This was set up so I could easily compare the unmodified digital source with the CEDAR gear's output signal. Digital monitoring was done, as usual, through a Wadia DAC.

The two analog sources were set up as follows: Reel-to-reel 15 IPS master tapes were played on two reconditioned vacuum tube Ampex 354 recorders, while 1/4-track stereo commercially produced product was reproduced on a vintage tube Tandberg 62 consumer deck (the same type of machine a well-heeled audiophile might have used to play those 7.5 IPS 1/4-track stereo tapes back in the mid-í60s). Since I was a poor college student in those days, I owned a little solid state Sony 350!

LPs were played on a restored vintage Thorens TD-125 turntable with a van den Hul reconditioned Koetsu rosewood moving coil cartridge, and preamplified by a McIntosh C20. Thus, both analog sources were played back on high-quality equipment contemporary with the media played on them, while the digital conversion and noise reduction gear were strictly from the late '90s.

I used only the DHX dehisser on my tapes, since none exhibited any clicks or crackles. I was fortunate to have on-hand both Dolby A and non-Dolby dubs of a particular master tape of the New York Ensemble for Early Music that I had sold to Nonesuch in 1978. I could compare them easily using two Ampex 354 decks. The dub made without Dolby A was definitely hissier than the Dolby dub but, with careful adjustment of the CEDAR DHX dehisser, sounded virtually identical to my 1978 noise-reduced copy.

The commercial prerecorded four-track tapes (duplicated by the AST division of Ampex in the '60s) that I played through the DHX showed noise reduction results of varying effectiveness. Those tapes, which were in good shape and had been duplicated well - and which also did not contain a lot of high brass content - fared pretty well.

One particular tape - the Ansermet recording of Debussyís La Mer - had an acetate base material that had not weathered the decades without incident. It showed inconsistent high-frequency response on the outside tracks due to tape cupping, and did not come through the CEDAR equipment unscathed. The DHX's DSP seems to prefer constant hiss levels and program material without a lot of spiky highs. According to the company, DHX is designed for constant hiss levels. For material with other broadband noise problems, CEDAR recommends its NR-3.

To adjust the DHX, crank up the level control until you hear what CEDAR describes as twittering (and that's exactly what it sounds like). Then continue to increase the control until a glugging sound (yes, again an apt description) is heard. Then tweak the knob for a happy medium between the two auditory anomalies and reduce the amount of hiss reduction until the anomalies go away.

Well, I could never get those Swiss trumpet players in Ansermet's orchestra to stop twittering without turning the noise reduction action off completely, so I gave up on that one. But all the other tapes I tried worked out satisfactorily.

Listening to some of my LPs (for the first time in about 20 years) was a fabulous experience. The DCX declicker is a miracle box. It has only one control and I just left it most of the way up. Remember all those tiny little clicks and pops that all LPs had (especially audible during quiet passages on classical records)? Well, this box simply makes them go away 100%! The only tradeoff is a slight loss in overall transient definition, but if your record isn't too clicky, and you set the control only halfway up, the sound doesn't degrade much at all. Incredible!

The CRX decrackler removes high-density ticks and also gets rid of surface noise, buzz and some forms of amplitude distortion (such as phono cartridge mistracking and other groove-wall/stylus interface problems). Once I learned to use the DHX and DCX, mastering the CRX wasn't difficult. I had feared it would be the hardest to use, because first one sets it up in a detect mode that gets rid of the crackles, but also introduces a gross side effect - a bubbly underwater kind of sound. Once crackles are minimized, however, you can make the bubbles go away by switching away from detect to decrackle.

With a little experience, I had all three units adjusted in a one-size-fits-all configuration and started playing my old records through them. A little tweak of the sensitivity control on the CRX or the level knob on the DHX quickly brought the sound of each LP into focus. It actually took less time than turning the record over and wiping off my van den Hul stylus. I had forgotten how much tweaking I did back in the analog days. I kind of miss that a little. The closest I can get to it in these digital days is to switch compulsively between different dither algorithms when I master. But that's another story.

The bottom line is that Iíve rediscovered my record collection. The last time I moved, it filled up 49 of those 1.5-cubic-foot moving boxes. It's not an inconsiderable pile of moldy oldies, a lot of which will never appear on CD. One of the main reasons I decided to become a recording engineer was that I simply hated the clicks and pops on my LPs, and wanted to have a supply of master tapes to listen to. Really, I kid you not! If this CEDAR gear had been around in 1969 I might have gone to medical school after all, and become a real doctor.

Summary

I used to know Dick Burwen pretty well, and in the '70s he designed some pretty cool single-ended noise reduction equipment. Dick was the smartest engineer I knew in those days, so Iím pretty sure he did the best he could, given the technology of the time. Well, let me tell you, his analog gear - which was very highly regarded in those days - doesn't do diddley-squat compared with this CEDAR stuff. Twenty-five years sure makes a big difference!

Dr. Fred Bashour holds a Yale Ph.D. in Music Theory, and is a classical music produce and engineer. He is a contributor to Pro Audio Review and hopes he will never have to move his record collection again.