11
tencies in timing) in the incoming digital information, the output of
the FIFO is controlled by a special clock with tremendous accuracy.
The result largely eliminates the jitter and allows the musical informa-
tion to be reproduced cleanly, without jitter-induced distortions.
The trouble with most FIFOs lies in their behavior when the incoming
signal is poor enough to cause the “water tank” to overflow or to be
emptied. Normally, a FIFO would then have to “invent” false data to fill
the gap, throw away excess data, or revert to non-FIFO operation. None
of these approaches are acceptable.
Of course, you could simply use an extremely large buffer. Unfortu-
nately, this solution is a poor one.
A larger buffer implies a longer delay between when information goes
in and when it starts coming back out. With laserdiscs, for example,
you must keep the in/out delay small so as to keep the soundtrack syn-
chronized with the picture on the screen. An oversized buffer would
make every movie’s audio out of step with its video, an unacceptable
situation. It is possible to bypass the FIFO for movies, but you then lose
all of its distortion-reducing benefits.
Madrigal engineers have developed a proprietary buffer management
scheme which reduces reproduced jitter to less than 20 picoseconds
while maintaining the synchronization of sound and picture in movies.
It employs a buffer large enough to absorb the jitter found in trans-
ports of reasonable quality, yet small enough to have impreceptible de-
lay. The rate at which data is released from the FIFO buffer is con-
trolled by software to track the long-term data rate of the incoming sig-
nal, allowing the buffer to absorb all the short-term variations which
cause sonic degradation. This approach yields a “smart” FIFO buffering
scheme which rejects virtually all incoming jitter without requiring an
enormous buffer and the consequent audible delay. It also avoids the
sonic penalties associated with the usual strategies used when a buffer
overflows or empties.
The Intelligent FIFO operates at all sampling rates, improving the qual-
ity of every connected digital source component.
Superior isolation
between sources
One of the advantages of a separate digital audio processor is that you
can take the money which might have otherwise been spent on several
built-in D/A converters and put it into one, superior processor which
will enhance the performance of all the transports with which it is
used. Ironically, many outboard processors fail to live up to this poten-
tial due to interference between their various digital inputs.
The Nº30.6 provides outstanding isolation between its inputs, realizing
the full potential of the various digital transports with which it is used.
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