Over Detection Threshold
The over detection threshold is the number of consecutive full-scale samples that constitutes a digital
"over". The Over indicator will increment when the threshold is reached. To avoid rapid saturation of the
counter, the DSP "times out" for one second after detecting an over, before detection is re-enabled.
*Truncation Logic is applied only to digital inputs such as AES/EBU and S/PDIF, which carry internal data about the sample length.
If an input is applied which, for example, identifies itself as "16-bit", then the truncation logic will discard any additional bits in
case they contain undefined data. If you are handling a signal in which the LSBs are used for some other purpose, however, and
wish to preserve them, you can turn the truncation logic off to ensure that the data are passed unchanged.
†SW7 is set to OFF (down) when the AD-8000 leaves the factory. In this default position, DC components are not removed from
incoming analog signals. The "over" threshold setting defaults to four consecutive full-scale samples. If you wish to remove DC
from analog signals, we recommend that you set the "over" threshold to one sample, ie set DIP switches 3 and 4 ON (up). If you
attempt to perform DC removal on analog input signals with the threshold set to a higher value, some overs may go unregis-
tered, because the DC removal circuitry interprets any analog clipping longer than a single full-scale sample as a DC component,
and consequently removes it before it can be registered as an over, if the over threshold is set to more than one sample.
Appendix II: About UV22 Super CD Encoding
Squeezing more performance from a digital recording is not a new idea. It began with adding white noise, called
dither, to the digital audio. Plain dither was followed by different flavors of dither noise, then a process called
'noise shaping', and various forms of so-called 'bit mapping'. Most recently, systems have been introduced that
store control information in the least-significant bits and use a special decoder to recover the data on playback.
Independent listening tests confirm that these systems either color the recordings we are trying to pre-
serve, or compromise the audible noise floor. Encode/decode systems may sound good if they are decoded,
but almost nobody owns a decoder!
Five years in the making, Apogee UV22 Encoding is an entirely different process. UV22 does its job with-
out sonic compromise, and without adding a sound of its own, preserving the sound stage and tonal balance of
the original high-resolution source. The effects are even audible on original 16-bit recordings.
UV22 Encoding adds an inaudible, high frequency 'bias' to the digital bitstream, placing an algorithmically-
generated concentration of energy around 22 kHz. Much as the bias on an analog tape recorder smooths out
magnetic tape recording non-linearities, UV22 silently captures resolution up to and beyond 20 bits on a stan-
dard, 16-bit CD. In addition, this inaudible carrier smooths the rough edges of even the most inexpensive CD
player or external converter. UV22 makes your recordings sound better on all listening systems. Running
already-mastered 16-bit sources through a UV22 processor delivers sonic improvements that any user can real-
ize on equipment they already own.
UV22 is a very special information carrier: it is not a new flavor of dither noise. The truly unique statistical
properties of UV22 guarantee a constant white noise floor, very similar in character to analog tape noise, no
matter what the input source. If you listen to the noise on a UV22 encoded recording, you can hear a stable,
accurate sound stage and faithful tonal balance more than 24dB into the noise – just as you do on analog tape.
Yet the UV22's low audible noise floor sits at the theoretical limit for a 16-bit system. Nothing is lost – but a
great deal is gained.
In listening test after listening test, engineers and reviewers alike choose UV22 over all other systems. Many
thousands of CD titles have already been mastered using Apogee UV1000 Super CD Encoders and the Apogee
AD-1000. Apogee's UV22 is today in use in the vast majority of US mastering houses, and it is estimated that
as many as 80% of the hit records mastered in the United States today utilize UV22.
The latest development in word-length reduction technology is Apogee's new UV22HR technology. The vast
increase in computing power over recent years has made it possible to completely re-work the UV22 process
from scratch, to produce UV22HR — "High Resolution". UV22HR retains even more of the detail of a high res-
olution signal while delivering, as before, a signal at the desired output word-length with the noise floor at the
AD-8000 Operating Manual