Equipment Review No. 3  MAR/APR/2001
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AMM Jisco Jitter Scrambling Decorrelator
  • Altmann Micro Machines
  • AM Muhlenbusch 57
  • 42781 Haan
  • Germany
  • +49 2129 52 260
  • SRP $500 w/ RCA/Toslink input;
  • $550 with ST optical
AMM Jisco Jitter Scrambling Decorrelator

Description and Specifications: Scrambles the jitter of the input signal and shifts it to higher frequencies for easier removal from the upstream digital component. Reduces audibility of transports and cables. Plugs directly into receiving device eliminating the need for extra cable. Works with any sampling frequency from 32-96 kHz and above. Accepts word length of 16, 18, 20, or 24 bits. Works with any digital source such as PCM, AC-3, DTS, MP3, etc. See above website for more thorough technical explanation of jitter and the workings of the Jisco. Has a 5 year warranty.

Equipment Used: NHT 2.9 (#2), Martin Logan SL3(#3) and Sequels(#1), Rotel RTC-965(#2), Rotel RB-985(#2), Mark Levinson No. 29(#3), Marantz DV7100(#2), PC computer w/ Sound Blaster Live! and Hoontech digital adaptor(#3), Rega Planet(#2), Sunfire Signature(#1), Theta Basic II(#1), Classe SSP-25(#1), Classe CP-60(#1), Meridian 568(#3), Harmonic Tech(#1), Goldmund(#1), Discovery(#3), Audioquest(#3), Monster(#2), and throw-away cables(#2,#3).

Listening System #1: Listening system 1 used the above equipment, and was tweaked by the owner (an audiophile buddy--Mel) to the nth degree. Isolation racks and cones, placement, cable matching, and power conditioning are all in place and have been optimized over years. While I was reviewing another product I loaned the Jisco out to Mel to break it in and see if he heard a difference in his system. He has several different digital cables that he has tried and has recently been using a Goldmund cable direct into the Classe SSP-25. This is connected to the Classe CP-60 and then to the amplifier. He was enthusiastic about the unit from the start, so I came over after a few days to hear how the unit performed. We put on track 1 and 2 from Patricia Barber's Nightclub Album and began switching back and forth. With the Jisco we felt the sound was noticeably smoother, bass was tighter, there was less edginess, and a slight roughness to the sound was removed. When we switched the Jisco out the voice became more sibilant and a bit more metallic in an unnatural sort of way. The piano was noticeably worse sounding which was confirmed when we put the Jisco back in.

On track 7 from Burmester Vorfuhrungs CD III, Rimsky-Korsakov's Scheherazade the differences took very little time to notice. Mel had been using the Jisco for days and could fairly easily pick it out blind (in System #2). With this cut the sound became less distinct, not as smooth, clean or sweet, edgier, and the noise of the recording was more noticeable with the digital cable direct. With the Jisco in again there was less "hash" and the sound was not as hard. No surround comparisons were done with this system.

Listening System #2: This was a more modest system and testing began with a cheap cable that comes with a VCR. The question is what the Jisco could do with a lousy cable, and if jitter would make a difference when the cable was not even designed to be 75 ohms for digital/ video use. The Marantz DVD player was used and connected to the surround preamp's digital input, and then to the amplifier. For fun I started with track 3 from Oldies But Goodies #10-Frankie Avalon's Venus. Even with this mediocre recording the sound was less edgy and more natural sounding with the Jisco. From Warner Archives Sampler, track 6, I put on Maria Muldaur's Midnight At the Oasis. Without the Jisco there was a loss of focus and the sound was harder and harsher. With the Jisco the details on this track came across better. Next up was track 1 from Massive Attack Mezzanine. With the Jisco the sound was smoother, more natural (if electronic music can be thought of as natural), and some of the edginess was removed. After a while I became concerned that the Jisco was removing high frequencies that were actually on the recordings, but with more listening with recordings that had a lot of space, ambience, reverb, etc., these remained intact. I'm not really sure why this would be, but it appeared to be the case.

The next change was to move from the DVD player to a Rega Planet with a Monster digital cable. I listened to track 1 from REM's New Adventures In Hi-Fi and felt the differences that were present earlier had been reduced. It was much harder to hear them even going back and forth several times. I focused on different instruments and/ or voice from certain timings on the track. There was a slight sibilance without the Jisco and with the Jisco there seemed to be easiness to the sound that was lacking without the unit. I went back to the Marantz, but kept the Monster digital cable. With track 6 from Firefall's Greatest Hits the voice had less edge, sound was more 3D, noise on the recording was less noticeable, and again there was an easiness that was missing without the Jisco.

I tried 2 tracks from 20th Anniversary Sampler from Chandos. Track 3 is Herbert Hamilton Hardy's Variations on a Dublin Air. Without the Jisco the sound was less focused, screechier, edgier, and I felt like there was something obscuring the music. I could hear the violin much better when the other strings were playing with the Jisco plugged in. With track 14, Franz Lehar's The Merry Widow, the balance seemed lighter and more liquid with more definition to the sound. The voices seemed to flow better and have a more natural sound to them.

Listening System #3: In the last listening system I had the hardest time hearing the difference made by the Jisco. It could be that the Meridian 568 was the least susceptible to jitter of the all the tested pieces. With track 10 from No Doubt's Tragic Kingdom there was a slight nasal quality that was gone when the Jisco was in place. I thought the guitar might also have sounded better, but it was hard to tell. Track 1 from Beth Orton's Central Reservation was steely, but in a more natural way, guitar was better, the voice was sibilant but not as much without the Jisco.

I tried a couple of DVD's with both DD and DTS sound (and in System #2). With movies it was really hard to hear differences, but your mileage may vary. I listened to both El Dorado and The Matrix, but ended up getting more caught up in the film, and had a tough time hearing the difference.

Conclusion: The Jisco comes all the way from Germany, so it's hard to say go ahead and check it out at your dealer and see if you like it. I can most assuredly say that in each system I tried the Jisco I never felt the sound was worse with it inline. But the differences heard varied from noticeable to barely audible depending on the various equipment combinations. My guess is the Jisco will have the most beneficial results with less expensive equipment - however it is less likely that anyone with a lot less expensive equipment will spend $500 on this type of unit. In system #2 (which was the least expensive), the improvement with the Jisco was definitely worth the cost. For people with thousands of dollars invested in a system and who care about extracting the last bit of performance, then the Jisco is something to seriously consider. The Jisco is very small, doesn't require extra cables, and will work with just about any type of input, so it can stay in your system regardless of what you listen to and what you have connected to it. When $1000 cables (or more) are commonplace in high-end audio these days, $500 seems like a small price to pay for the improvement in sound that the Jisco offers.

- Brian Bloom