TM
dbx Type IVWhite Paper
504X
dbx Type IVa Conversion System
White Paper
by Roger Johnson
The dbx Type IVa Conversion System is a proprietary analog-to-digital
(A/D) conversion process that combines the best attributes of digital con-
version and analog recording processes to preserve the essence of the ana-
log signal when it is converted to a digital format. dbx Type IVa not only
exploits the wide linear dynamic range of todayOs A/D converters, but also
enhances it and extends the useable dynamic range beyond the linear
range. By providing a logarithmic OType IVa Over Region� above the lin-
ear A/D range, we benefit from the extended high-level headroom that is
inherent in analog recording without compromising the noise performance
of the A/D conversion process.
Digital conversion and recording processes proliferated in the 1980Os
primarily due to the Ocleaner� sound of digital versus analog, an advantage
resulting from the comparatively wider linear dynamic range of digital.
Anyone who is familiar with the technical specifications of digital equip-
ment knows that the typical maximum signal-to-noise specifications for 16-
bit systems is in the neighborhood of 90-something dB. Compare this to
the typical signal-to-noise specifications for professional analog tape of
about 55 dB without the aid of noise reduction and around 75 to 85 dB
with noise reduction such as dbx Type Ia or Type IIa applied.
This seemingly tremendous signal-to-noise advantage of digital over
analog would suggest that digital would become the unanimous choice for
recording. For the most part this has occurred, not totally due to its signal-
to-noise advantage, but as much due to the benefits of digital storage such
as random access and the inherent ability to withstand degradation, unlike
that of analog tape or LPOs. In spite of the benefits of digital, no one in the
audio world can refute the rediscovery of analog recording and tube gear
that has occurred in the 90Os, attributable to the quest for that Oanalog char-
acter� that is missing from digital recordings. This continued use of analog
gear with modern digital systems brings to light a favorable characteristic
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