Alesis ADAT-XT20 User Manual download pdf (Page 40)

Connections: Chapter 3

ADAT XT20 Reference Manual 39

DIGITAL AUDIO IN/OUT

The digital input and output carries all eight tracks on a single fiber optical

cable. This allows you to bounce audio between multiple machines within the

digital domain. The ADAT Optical cables carry digital audio between

multiple XT20s and ADATs, and to ADAT Compatible™ products such as the

QuadraVerb 2, Q20, many Alesis keyboards, the ADAT-PCR computer interface

card, and third-party products such as the Digidesign ADAT Interface and

Yamaha 02R digital mixer. Since the fiber optic connector carries the digital

information for all 8 tracks, it is also useful for backing up all tracks in one pass

(see Chapter 6 for more on digital audio).

Digital bussing requires a fiber optical cable (included) for each XT20 in the

system (or any other ADAT-compatible product). Additional cables are

available from your dealer in various lengths up to 16 feet. This connection can

be made while power is on or off, and the machines do not need to be turned on in

any particular order. Note: To bounce tracks within a single XT20, it is not

necessary to connect the optical network.

ABOUT 16-BIT AND 20-BIT SIGNAL TRANSFERS

All data on the ADAT Optical cable is in a 24-bit word length; in 16-bit

mode the eight least significant bits are filled with zeroes, in 20-bit

mode the last four bits are zeroes. If 20-bit data is sent to a 16-bit

machine, the four “extra” bits are simply ignored. Only ADAT Type II

machines (such as the M20, XT20, LX20, and PCR card with proper

software) can receive a full 20-bit transfer via the optical cables (and

then only if the tapes in those machines was formatted in 20-bit mode).

If you need to transfer audio from a Type II tape to a Type I tape you

have three options:

❿ Transmit at 20 bit, and the receiving unit will ignore the last

four bits, essentially cutting them off.

❡ Press the [DIGITAL OUT] button (located on the right above

the RECORD button) until the display reads:

ABS

Ovt 16

This cuts off the data in bits 17-20 and fills the “extra” 4 bits

with zeroes at the transmitting end. In most cases, this has the same

sonic results as Method #1.

① Press the [DIGITAL OUT] button (located on the right above

the RECORD button) until the display reads:

ABS

Ovt 16dt

This adds dither, a specially shaped mathmatical noise, to

the conversion process which “smoothes out” the transition at low

levels and allows you to get better resolution even though the result is

still 16-bit. However, if the signal will be dithered again later, you

may want to use one of the first two methods.

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Alesis ADAT-XT20 User Manual Page 40

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