You are now the proud owner of one of the finest D/A converters ever built. The Bidat is the digital-to-audio converter which culminates over eight years of effort by Ed Meitner and his design team. The result is a world-class digital audio system for studio and home use. In the course of this continuing research, attention has been devoted to every detail of the digital-to-analog conversion path. The innovative engineering behind this product has achieved recognition in the form of several patents and through a technical paper presented to the Audio Engineering Society.
The following items should accompany your Bidat in its shipping carton:
If any of the above are missing please contact your dealer or our service support group.
1. On the
bottom of the Bidat, located under a removeable cover plate, is
a set of mini-switches. These switch positions are read by the Bidat
on power-up to determine the default configuration settings of the system.
2. The Bidat is factory configured with switches 4 and 5 ON and the rest OFF.
3. This defines default operation with a 75 ohm coaxial input, true phase, and no remote volume option. It is not necessary to change these switch settings before operating the unit unless the optional wire remote is used.
Should the operation of the unit be disrupted by static electricity or a power line disturbance, press the reset button (RST) on the back of the unit. If this does not rectify the problem, power the unit off, then on again.
"Since the ear is a velocity sensitive device, it will respond to time changes much more readily than amplitude changes."
"Frequency changes and timing are fundamental characteristics of music. These attributes are critical to the accurate reproduction of sonic information."
Sounds which have been digitally recorded (i.e. quantized in time and magnitude into digital words) must be decoded at an equivalent sample rate and magnitude in order to accurately reproduce the original sounds. The stability of the sample rate clock directly affects the accuracy of conversion and it is easily shown by calculation that the required clock stability at 8Fs can be no worse than 50pS peak-to-peak in order to achieve 16-bit accuracy. This kind of deviation from perfect clock stability is called phase jitter or time jitter.
The accumulation of jitter through the playback chain is examined in a AES technical paper entitled "Time Distortions within Digital Audio due to Integrated Circuit Logic Induced Modulation (LIM) Products" in which the mechanism of jitter propagation called LIM is identified and a Museatex measurement tool for jitter analysis is introduced.
This research has led to the development of a series of proprietary Museatex circuits which prevent or reduce jitter in digital audio systems. An audio D-to-A converter must by necessity derive its timebase from the input audio data. The recovery of this clock is usually performed by one of a handful of standard IC's, all of which are sensitive to degradation of stability by every component of the preceding playback chain including the interconnecting digital cables. Yet the overall performance of the converter depends critically on the clocking of the conversion IC's with a clock having very low jitter.
C-Lock-R is a proprietary data receiver which uses a radically different clock recovery method. It has low sensitivity to jitter and LIM products carried in the received data stream. This provides the Bidat with low- jitter system clocks having high immunity to LIM and jitter caused by the sourcing equipment. Furthermore, this circuit ensures that any remaining jitter has a random or "white" frequency distribution allowing for clock distortion accuracy below the 20-bit level.
Museatex has made this receiver available under license to interested parties.
C-Lock-T is a proprietary reclocking circuit which ensures that jitter is removed from digital outputs. This circuitry has received critical praise as used in the Museatex Melior CD-Deck, a unit which outputs a fraction of the jitter produced by competing high performance drives costing many times more.
Other C-Lock jitter attenuators are used to ensure that the D-to-A conversion IC's in the Bidat are driven with sufficiently stable clocks.
" The only true happiness comes from squandering ourselves for a purpose."
William Cowper 1731-1800
" ...There is still another way of designing a digital processor: Junk the off-the-shelf parts, forget about "standard implementations", and trash-can conventional thinking. This designer is going to completely rethink the role of each stage in a digital processor and invent entirely new circuit topologies to overcome the limitations he sees in standard components and techniques. If our first engineer designing by application notes, produces a product equivalent to a paint-by-numbers painting, this last designer is like the master who creates a whole new movement in art."
Stereophile. March, 1993.
In January, 1993, the Meitner IDAT (Intelligent Digital Audio Translator) was introduced to the audio market with a price tag hovering around 15,000 dollars. It met with rave reviews around the world. At the same time as IDATs were being produced, Museatex was launching a project that would incorporate the IDAT algorithm and design features into a less expensive product: the Baby Idat, or Bidat.
The Bidat, at a fraction of the cost of its predecessor, now outperforms it.
At the heart of the Museatex Bidat is a unique and proprietary digital filter algorithm which processes digital audio information using two DSP microprocessors. As the name implies, this algorithm examines the digital audio data and makes an intelligent determination on how best to up sample this data to an eight times over sampled rate (8Fs, 352.8KHz for CD) while maintaining unequaled faithfulness to the sounds originally recorded.
Other manufacturers who have designed their own digital filters have mostly used algorithms similar to the textbook topologies found in the commonly available filter IC's. A few have made attempts to optimize their filters by concentrating on transient response accuracy and have done so by sacrificing their frequency response.
There are other designs which claim optimization of both time and frequency responses but nonetheless exhibit audio artifacts similar to those produced by the standard mass-market filter IC's; principally a symmetrical ringing at 1/2Fs which occurs before and after each transient and is known as Gibb's Phenomenon
The Bidat algorithm analyzes the digital audio samples for relative accelerations and then chooses the type of filter most appropriate for that segment of data. This intelligent process results in a frequency response which is flat to 20KHz for CD playback. More important, it produces a uniquely pure impulse response without Gibb's ringing. For example, a square wave will have clean rectangular transitions and no ringing.
The Museatex Bidat
can claim transient response demonstrably MORE faithful to the recorded signal
than the best analog playback systems for vinyl LP's and open-reel tapes. The
undistorted transient response of the Bidat means the algorithm contributes
no coloration of its own to the processed audio. This performance eliminates
the "digital washout" of sonic subtleties and the harshness heard
in listening to a conventional interpolating algorithm. For the first time in
audio engineering, the full advantage of Digital Signal Processing has been
used in the service of signal fidelity by the implementation of a smart filter
which could never have been built with analog circuits.
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