Chapter 10 - Multiple LX20/ADAT Operation
INPUT MONITORING
The ADAT LX20 monitors the input signals through the A/D and D/A converters at
all times. This lets you hear eactly what the audio will sound like when itOs
played back from tape. However, thereOs a minuscule delay as the digital audio
passes through the convertersO buffers. If you monitor both the original signal and
the tape return of the same signal coming back from the LX20 through your mixer,
the LX20Os delay would cause some phase cancellation when combined with the
original signal. Therefore, it is important that you monitor either the original
signal or the tapeOs input signal on your mixer, but not both.
POLARITY DIFFERENCES
The original ADAT inverted the polarity of the signal being recorded on tape, then
flipped polarity again before going to the output jacks. As a result, the output was
the same polarity as the input, so no phase problems were possible when using a
single ADAT or a multiple ADAT system.
However, neither the digital input nor the digital output was inverted. Therefore,
if you digitally transfer the ADATOs digital audio data to a DAT machine or hard
disk recording system, the audio output from the other device would likely be out of
phase with the ADAT, since it probably does not invert the analog signal after its
D/A converters. Although this is not usually a problem, it may cause some confusion
when mixing multiple audio signals from multiple sources, since there is a
possibility that signals could become out of phase.
To prevent this from occurring, the LX20 design has been improved so that the
polarity remains constant from the analog to digital, and back to analog, domain.
Like the original ADAT, the result from one machine, or multiples of the same
machine, is the same: The input to output phase is correct. However, if two cloned
tapes (copied digitally either with ADATs, ADAT LX20s, or both) are played back
in sync on both an ADAT and an LX20, the outputs of the two machines will be out of
phase relative to each other.
The only known situation where this could cause a problem is as follows:
Suppose you had been using a multiple ADAT system and you recorded a stereo
signal across two machines (e.g., a stereo drum recording on tracks 8 and 9), where
there is a common element to each track (i.e. center signal). If you replace one of
these machines with an LX20 but play back the same type, the track playing back
from the LX20 will be out of phase from the track played on the ADAT, canceling
the center signal.
ADAT LX20 Reference Manual 63 |
ACEC
