The dbx Type IV™ Conversion System is a proprietary analog-to-digital (A/D)
conversion process that combines the best attributes of digital conversion and analog
recording processes to preserve the essence of the analog signal when it is converted to a
digital format. dbxType IV™ not only exploits the wide linear dynamic range of today’sA/D
converters, but also enhances it and extends the useable dynamic range beyond the linear
range. By providing a logarithmic“Type IV™ Over Region”above the linearA/D range,we
benefit from the extended high-level headroom that is inherent in analog recording without
compromising the noise performance of theA/D conversion process.
Digital conversion and recording processes proliferated in the 1980’s primarily due
to the “cleaner” sound of digital versus analog, an advantage resulting from the compara-
tively wider linear dynamic range of digital. Anyone who is familiar with the technical
specifications of digital equipment knows that the typical maximum signal-to-noise specifi-
cations 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 dbxType I™
orType II™ 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 LP’s. 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 90’s,attributable to the quest for that“analog character”that is missing from
digital recordings. This continued use of analog gear with modern digital systems brings to
light a favorable characteristic of analog recording which those who abandoned analog and
jumped on the digital bandwagon were either never aware of or simply took for granted.
Anyone who has ever used analog tape knows that you can “hit it hard” without
destroying the recording. The printed specifications of analog tape don’t take into account
the practical headroom available. The max signal-to-noise specification of analog tape is
measured by defining the“max”signal as the point where a given signal level and frequency
produces a given percentTotal Harmonic Distortion (THD)—typically the level at which a
1 kHz signal produces 3%THD. In actual use,the signal can easily exceed this“max”signal
level by 5, 10, or even 15 dB on peaks, depending on the type of signal being recorded,
without unacceptable artifacts. High signal levels can be tolerated (i.e.more headroom) at
the expense of increasedTHD which,incidentally,is often desirable as an effect,evidenced
by the renewed popularity of tube equipment.
The obvious conclusion is that analog recording actually has more useable dynamic
range than the specifications seem to indicate. For example,let’s say we’re recording a kick
drum. If analog tape measures 55 dB from the 3%THD point down to the RMS noise floor
and the peaks of the kick drum exceed the 3% THD level by,say,15 dB and it still sounds
good,then we have 15 dB of extra useable headroom. Therefore,we end up with 70 dB of
useable dynamic range. Throw in noise reduction and we push into the 90-something dB
dynamic range territory of 16-bit digital. This explains why well-recorded analog master
tapes make good-sounding CD’s with no objectionable noise.
One main drawback of digital is that it inherently lacks this forgiving and beneficial
characteristic of analog recording. Although digital conversion exhibits wide linear dynamic
range,when you run out of headroom for high-level signals,hard clipping or even ugly signal
Type IV™ Conversion System White Paper - August 1998 Page 1
dbxType IV™ Conversion System
