Lexicon 300, Owner'S Manual

Page: 78 / 155

Lexicon
300 V 3.0 Owner's Manual
4-22
Stereo Adjust DC Offsets Page
This control provides three choices: RESET, MANUAL ADJUST and AUTO
ADJUST. RESET disables all DC adjustment. AUTO ADJUST enables routines
for correcting DC offset from material recorded through analog-to-digital con-
verters that are not properly trimmed for DC. MANUAL ADJUST allows Softknob
selection of offset values.
Replaces any previously obtained value with the value set here via the soft knob.
The display indicates the percent of the correction.
SHUF controls a spatial equalizer designed to make recordings from a dummy
head, or closely-spaced omni microphones, more suitable for loudspeaker
reproduction. Due to the close spacing of the microphones, there is very little
difference between the two stereo channels below about 300Hz. The shuffler
restores the low frequency separation by first matrixing the L and R signals into
L+R and L-R, bass-boosting the L-R channel, then rematrixing back to L and R.
The effect is to convert small time differences (which are not audible in
loudspeaker reproduction) between the two microphones into level differences,
which are audible. The effect can be dramatic.
The frequency below which the boost acts is set by the SHUF control. A setting
of 5 will give a 3dB L-R boost at about 150Hz; a setting of 10 will be 3dB up at
250Hz. Response rises at 6dB/octave below this frequency. More than 18dB of
gain can be obtained at 20Hz when SHUF is set to 10.
This control has been optimized for true binaural recordings, where the differ-
ence signal at low frequencies is minimal. If it is used on ordinary stereo material,
or with binaural material to which reverberation has been added, excessive low
frequency difference signals can result. On such material, it is better to use the
SPEQ control which will achieve a similar result.
The SHUF control varies from 0 (shuffler off) to a maximum of 10. While theory
would suggest a setting of 10 for a dummy head, a setting of 5 appears to be more
useful in practice. The setting is very much a matter of taste. If closely spaced
microphones are used, the setting will scale inversely with the microphone
distance in centimeters. For a spacing of 15cm, try a shuffler setting of 5. For a
spacing of 30cm, try a setting of 3. For a spacing of 7cm, try a setting of 10.
DCSW (DC Offset Nulling)
L-DC and R-DC
(Lch and Rch DC Offset)
SHUF (Binaural Shuffler)