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User’s Guide
6200 Digital
Voice Processor
To download the latest version of 6200 Designer, a Windows GUI
application interface for the 6200, go to: www.airtoolsaudio.com
TM
Symetrix
Engineered by
AGC:
AGC or Automatic Gain Control is a special case of a compressor with its threshold set at a very low level, moderate to slow
attack times, long release times, and low ratios. It is intended to take signals of indeterminate levels up to a target level while
maintaining program dynamics. Most AGCs incorporate some sort of silence detection to prevent the loss of gain reduction
during silent periods. This is the single feature that separates an AGC from a common, ordinary compressor/limiter.
Use an AGC to remove some of the variation in level from a person who isn’t trained on microphone control or to take some of
the guesswork out of setting up dynamics control of unfamiliar input sources. When setting up the AGC, keep the attack and
release times conservative (perhaps 50ms/500ms for voice and 500ms/500ms for music).
When engaging the AGC mode of the Compressor, some controls are repurposed, removed or replaced:
AGC Detector Thresh - The AGC Detector Threshold, or more accurately the AARM (Automated Attack and Release
Monitor) Detector Threshold, is a fixed threshold below which the AARM circuit stops calculating changes in gain. When
the input signal level is below the threshold, the AGC gain/attenuation will be locked, and therefore will not be changing.
Set this threshold to a level 10-20dB above the noise floor of your input signal. It can be dangerous if the threshold
is too close to the noise floor, as this could cause the noise floor to be raised in some cases. (Effective in AGC mode
only).
AGC Goal - The desired output signal level to maintain. (Effective in AGC mode only).
Compressor Threshold - This parameter is disabled in AGC mode.
Compressor Ratio - This parameter is disabled in AGC mode.
Compressor Makeup - This parameter is disabled in AGC mode.
LOW PASS FILTER:
Low pass filters allow selectively modifying a signal by attenuating all signals above a specified cut-off frequency. They can be
useful to remove noise or other unwanted frequencies. A low pass filter in a voice processor is typically used to limit the high
frequency content sent to downstream processing or the transmitter. The 6200 offers 6 dB/octave, 12 dB/octave, 18 dB/octave
and 24 dB/octave filters. Additionally, “peak” versions of each filter are provided for further flexibility and tuning. The filters with
the steeper response filter more sharply.
Controls:
Bypass/Enabled - When bypassed, the input is sent unmodified to the output. When enabled, the module processes the signal.
Low Pass Frequency - Determines the cut-off frequency of the filter. All frequencies above this will be progressively attenuated.
Technically, this frequency is the “3 dB down point”, i.e. the point where the filter response is 3 dB lower than it is for unaffected
signals.
LP Filter Slope - Determines the type of filter (slope) to use in order to select how steep or aggressive the filter is.
Technical note: The module implements Butterworth filters which are generally preferred for audio because of their flat
frequency response in the pass band.
OUTPUT:
The final “DSP Module” is the output level. The output is loosely labeled a DSP Module as the level adjustment does happen
in the digital domain within the DSP and its parameters are stored within the programs, however, it can not be reordered or
bypassed/enabled as the other modules can. The output level provides the final gain stage before the physical output(s) of the
unit and has a range of -72.0 dB to +24.0 dB. Typically, this control would remain as close to 0.0 dB as possible using it only
for level matching to downstream equipment or to compensate for gain added or subtracted by the upstream DSP modules. If
it is necessary to connect the output of the 6200 to a microphone level input, see Appendix A for information on converting the
6200’s line level output(s) to mic level.
OUTPUT METERING:
You can monitor the output meters by viewing the “Out LVL” menu accessed by pressing the HOME button once then turning
the ADJUST knob clockwise twice. A meter for channel 1 is displayed on the top line, channel 2 on the bottom line. Unity gain
is represented as an “open square” symbol and corresponds to an output level of -20 dBFS = +4 dBu = 0 VU.
DSP MODULE WRAP-UP:
That covers the available DSP modules and their controls. For a graphic view of the menu structure, see Appendix B.
DSP Modules...
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