421m
9
Note:
Do not use pink noise or sine-waves for setup. It simply will not work (the ARM circuitry
will think your signal is noise). Use speech or music.
Helpful Hints
Microphone Techniques
Note: The ability of the expander to discriminate between wanted and unwanted signals is partially
determined by mic technique. Be particularly careful of high frequency sounds entering the side or
rear pattern of a cardioid mic. Most cardioid mics exhibit a sharply rising off-axis response charac-
teristic at higher frequencies. Check the off-axis curves in the manufacturer’s literature. If there’s
only a 3dB - 6dB difference between the on-axis (frontal) response and the off-axis (side) or rear re-
sponse in the 5kHz to 10 kHz region, high frequency sounds will be picked up by the mic, thereby
possibly preventing the downward expander from reducing unwanted sounds.
Use the mic’s directional pattern to keep unwanted sources as far off-axis as possible. Do every-
thing you can to discriminate against unwanted sounds through good mic technique. The sounds
picked up by an individual mic must be primarily the sound of the desired signal or the 421m’s
downward expander won’t be able to discriminate between signal and noise.
Optimizing Control Settings
When searching for optimum control settings, here are a few rules to follow:
AGC-LEVELER: The FAST setting of the RECOVERY RATE button is best suited for speech sig-
nals. Use the SLOW setting for musical or noisy signals or if you want the gain changes to be as
unobtrusive as possible.
The RATIO control determines how much of the input signal’s dynamic range makes it to the out-
put. We recommend starting at 4:1, so you can clearly hear the effect, and then reduce the ratio if
necessary.
AUTO-RELEASE LEVEL (ARL): This control determines the signal level needed to cause gain re-
lease in the AGC-Leveler. A suggested method of setting it is, with no signal present, increase the
setting of the ARL control until the green ACTIVE LED extinguishes. Then, further increase the
control setting slightly.
For musical signals use the SLOW setting of the RECOVERY RATE button. Set the AUTO-RE-
LEASE LEVEL control so that the ACTIVE LED is extinguished during low level musical passages,
fade-outs, or moments of silence.
DOWNWARD EXPANDER: When using the AUTO setting of the downward expander, first set
the AUTO-RELEASE LEVEL control in the AGC-Leveler section. Then use the expander’s RE-
LEASE control to prevent expander action during short pauses.
General PA System Considerations
In a public address system, it is important to ensure that feedback cannot occur when the AGC-
Leveler reaches a state of maximum gain; for instance, when the 421m is trying to boost the volume
of a very quiet voice. Avoid this by talking into the mic just loud enough for the ACTIVE LED to
light. If you hear feedback, then raise the AUTO-RELEASE LEVEL until the feedback dies. Lower-
ing the RATIO will also help. Remember: The ACTIVE LED does not
have
to be on constantly
while signal is present. In fact, depending on your circumstances, you may elect to set the AUTO-
RELEASE LEVEL high enough to prevent the 421m from responding to all soft voices.
Stereo Link And Bypass Switching
The STEREO LINK and BYPASS buttons interact. In stereo mode, the designated master unit
takes over all functions for both units, including in/bypass switching.
If the STEREO LINK button is in the out position, the 421m is in slave mode which means the 421m
gets its commands via the link cable from the master unit.
Note:
If a 421m is placed in SLAVE mode and is not connected to another 421m via a linking cable,
the unit will remain in BYPASS mode regardless of the setting of its BYPASS button. If there is a master
unit connected, then the BYPASS button on the master determines the status of the slave.
