There are several questions that arise, when dealing with jitter attenuation devices; these are e.g.
1) If I use a jitter attenuation device like the AMM-UPCI (or other), will I still be able to hear differences between different transports, different cables prior to the attenuation device or different CDs containing the same digital data (e.g. CD vs. CD-R)?
2) If I have multiple sources of program material, that have different sampling rates (CD, DAT, DVD) and are connected to a single DAC, do I need a sepearate standard jitter attenuation device for each sampling rate?
3) Can I use a standard jitter attenuation device in a multichannel, Dolby Digital or DTS application?
4) Can I use a standard jitter attenuation device in varispeed (DJ) applications?
In order to overcome all of the above limitations ALTMANN MICRO MACHINES has developed a new proprietary technology called:
JITTER SCRAMBLING DECORRELATION
The worlds first device incorporating this new technology, the AMM-JISCO (patents applied for) is in production now and can be ordered from this website.
The AMM - JISCO should not really be called a jitter attenuator, because the peak to peak jitter at the output of the AMM-JISCO is larger than the jitter at its input. It is not important to have low jitter at the digital input of the DAC receiver, however, it is very important to have low jitter at the actual DAC-chip, in the DAC device.
You can read in the following lines, to see how this is accomplished.
We will discuss its function with respect to the following block diagram:
(This is a strongly simplified block diagram. The actual implementation requires additional functions and associated circuitry.)
The incoming signal (2) (e.g. CD or DVD or SACD or DAT etc. transport /player) passes the jitter decorrelator block (4), that executes the real-time scrambling algorithms.
A modulator (6) performs a jitter frequency shift of the decorrelated signal using an ultra stable high frequency generator.
The jitter at the output of the modulator (3) has its energy shifted to higher frequencies, where it has no influence on the clock recovery PLL of the receiving device. This could be a DA converter, DAT recorder or AD converter, etc.
Specifically, what happens is this: Every receiving device (e.g. a DA or AD converter) has at its input a clock extraction PLL (in order to divorce the clock and data signal from the S/PDIF or other input stream). This clock extraction PLL is implemented into a receiver chip (e.g. the Crystal CS8414) and has its own jitter attenuation characteristic (see the CS8414 datasheet on page 8). This internal jitter attenuation is very ineffective in practical situations, because no attenuation is performed below jitter frequencies of approximately 10kHz.
Unfortunately CD and other transports generate lots of jitter below 10kHz.
If you take a second look at the jitter attenuation diagram of the CS8414 data sheet, you will see that relatively good attenuation is performed at 1MHz and you can interpolate that attenuation will be much better at even higher frequencies, not printed in the diagram (the designers of the CS8414 could not know, that we can exploit this feature now).
After scrambling the incoming jitter, the AMM - JISCO shifts the jitter into a high frequency range of several MHz. The receiver chip of the following device is able to strongly attenuate this jitter, so that the actual jitter at the DAC chips is low and NOT CORRELATED TO THE SIGNAL SOURCE. This principle works with all receivers and clock extraction PLLs since it is a common design necessity of any PLL circuit that the loop filter attenuates higher frequencies.
It can be said that this introduces a seeming paradox: By generating large amounts of jitter, the actual jitter at the DAC chip is reduced. The jitter paradox. This is how the ultimate goal, of low jitter at the DAC chip, is accomplished.
Due to the scrambling facilities of the AMM-JISCO, the signature of a signal transmitter (e.g. CD transport) will be attenuated. That means, that the perceivable differences between different transports, digital cables, CD/CD-R are strongly reduced and are less obvious compared to conventional jitter attenuation.
The JISCO technology is independent of sampling frequency, data size and data format. Therefore one single AMM-JISCO device is able to process 32, 44.1, 48, 96, 192 kHz or any value in between at any data size. It is also able to process varispeed signals (slowly changing sample rates) and other than S/PDIF formats (e.g. Dolby Digital, MP3).
We were shocked.
Since we had some experience in designing jitter attenuation devices, we were surprised about the sound quality available through the JISCO technology.
In all listening tests, regardless of data format or equipment, the AMM-JISCO device always delivered superior sound quality compared to conventional jitter attenuation devices.
It will also greatly improve the sound quality of integrated CD players with a digital output and input. The AMM-JISCO can be attached using either coax or TOSLINK connectors. Normally, a TOSLINK connection is not a prefered choice for connection. However, due to the scrambling feature in the decorrelation block, of the AMM-JISCO, the jitter components normally generated with a TOSLINK connection, are rejected in the AMM-JISCO processing.
It should be noted that the internal signal path of a CD-player is not able to deliver as high a sound quality, as an external signal path that includes the AMM-JISCO processing. This is true, even though an external signal path has traditionally introduced additional jitter, such as with a Toslink connection.
According to our knowledge at this point in time, and according to the results of numerous tests with all kinds of equipment, we can confidently state the superior advantages of our new JISCO technology in one sentence:
If you are not using the AMM-JISCO technology, your audio quality is not as good as it could be.
Several units of the JISCO have now been shipped to customers worldwide. We have received links to some reviews, that we would like to share with you:
Below are some interesting reviews, that I got from customers by email.
We are currently shipping the JISCO-MKII which has a higher scrambling frequency (50MHz) compared to previous model JISCO.
The price is EUR 1200,- for the JISCO-MKII with TOSLINK or RCA (Cinch) input.
Update price from JISCO to JISCO-MKII is EUR 550,-
The AMM - JISCO-MKII is covered by a 5 years limited guarantee.
Payment is prepaid to our account.
We will pay World Wide Shipping for You!
No matter, where you live. We will pay the price for a standard world wide air parcel. Delivery will take 5..10 business days.
Please order by email.
Text (c) by Charles Altmann