Output Resolution Selection And Uv22; Timing And The Ad-1000; Selecting The Internal Crystal Sync - Apogee AD-1000 Operating Manual

In 16 position: the signal is converted at 20 bits but is reduced to a 16 bit output by adding dither to
remove the distortion of truncation.
In UV16 position: the signal is converted at 20 bits and processed using Apogee's UV22 process to capture
the resolution and detail of the 20 bit source in a 16 bit word.
Apogee's UV22 is used by virtually all major mastering facilities for 20 bit to 16 bit reduction for CD mastering.
With the AD-1000, this process is available for all analog inputs. Two types of UV22 processing are available,
Normal and Low. The Normal position is used almost exclusively. When the recorded signal is to be processed
through UV22 more than two or three times, it might be beneficial to use the LOW setting. This setting cap-
tures almost as much detail as the NORMAL setting but has 6dB less energy. Further information on UV22 is
contained in Appendix I.
Unless your AD-1000 has the UV22 Digital Through Option, when in digital mode, the resolution of the output
is equivalent to the digital input's resolution. Additional information on the AD-1000 UV22 Digital Through
Mode and other Enhancement Options can be found on page 35.
Channel Status
The AES/EBU and S/PDIF formats are very closely related. The main differences are output level, impedance
and some differences contained in a repeating train of data packed in with the digital audio. The data are called
channel status. This train of information contains codes to tell digital audio products information such as
whether it is AES/EBU or S/PDIF format, sample rate, pre-emphasis applied or not applied, if copying is per-
mitted, etc. Most of the information transmitted in the channel status is transparent to users. The two main bits
of information that may matter are: a) The data defining AES/EBU or S/PDIF format; and b) The data defining
whether a copy can be made or not. Consumer-format copy protection systems are outside the scope of this
document, and the copy-protection bit settings of the AD-1000 are not user-adjustable.
Selecting Sync Source and Sampling Rate
When recording digitally, it is necessary to select an appropriate sample rate either independent of other equip-
ment or locked to an external reference. The AD-1000 is very flexible, with very accurate internally-generated
sampling rates and its ability to lock to a wide range of external sync sources. The AD-1000 can also act as a
stand-alone sync generator.
Internal Crystal Sync
A 'crystal' is a thin piece of quartz cut very precisely to vibrate at a very accurate frequency in an electrical cir-
cuit. The crystal inside the AD-1000 vibrates within plus or minus ten parts in a million (PPM) of the specified
frequency. This translates to less than 0.5 Hz error at 44.1kHz which is equivalent to less than one-fiftieth of a
cent at A440.
When the sync source is set to crystal (o), the sample rate switch is active in any of the sample rate positions
marked with a solid dot (•). Illumination of the appropriate sample rate LED indicates lock.
Locking to External Word Sync Inputs
The AD-1000 locks to external word sync inputs (also known as Word Clock or WC). In this sync source mode
the AD-1000 normally outputs the same frequency as the Word Clock connected to the Sync Input. Termination
can be applied using the 75 terminator supplied with the AD-1000 and applied to the unused BNC connector.
The AD-1000 SAMPLE RATE selector should be in the unmarked position (6 o'clock straight down).
AD-1000 Operating Manual

Timing and the AD-1000

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