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4 In / 4 Out Digital Audio Processor
Rio Rancho, NM – USA
OPERATING INSTRUCTIONS
Since all of the parameters used to set up the DSP4/4 are adjusted using the DSP4/4 Software Control Panel, the
operating instructions include instructions for the use of the software. It is recommended that you have the software
running, either live or in the demo mode, as you read through this section.
Using the DSP4/4 PC Hosted Control Panel
The DSP4/4 control panel may be used in one of two ways. When launched from the LecNet Master Pro application,
you can control all the parameters of the DSP4/4 in real time. Needless to say, your PC must be connected to the
DSP4/4 using the supplied LecNet serial cable in order for this to happen. Alternatively, you can launch the DSP4/4
control panel directly and it will automatically come up in the demo mode. The demo mode is useful for doing system
setup (and saving the setups to a disk file) without the need to be connected to a DSP4/4.
System setup and audio signal flow follows the order of the tabs on the control panel from left to right. Start at the
left tab and work your way to the right Please refer to the DSP4/4 Control Panel Software section of this manual for
a complete description of each control panel tab.
The DSP4/4 Block Diagram on page 3 represents the signal flow of one input to one output through one matrix
crosspoint. Illustrated are all the gain control points in the signal path.
To adjust this parameter:
Use this control:
Input Gain
Input gain tab on DSP4/4 control panel software
Rear Panel (Input) Gain
Programmable inputs on DSP4/4 rear panel
Crosspoint Matrix Gain
Crosspoint Matrix tab on DSP4/4 control panel software
Output Gain
Output gain tab on DSP4/4 control panel software
Rear Panel (Output) Gain
Programmable outputs on DSP4/4 rear panel
Each input channel has two gain control points. The input control point labeled “Input Gain” is adjusted using the
Input Gain tab on the DSP4/4 control panel. This control is used to adjust the sensitivity of each line level input to
the desired gain. The gain adjustment range is +10dB to -68dB plus off.
The input control point labeled “Rear Panel” represents the gain adjustments which can be made from the rear panel
programmable inputs. The rear panel gain control is attenuation only, starting at a maximum gain of 0dB. The rear
panel input gain controls may be limited in their adjustment range using the Input Gain tab on the DSP4/4 control
panel. In addition, you may set a rear panel preset gain value that will be applied to any inputs which are being
controlled by a programmable input. The preset gain is applied at power up. Note that if there are no limits applied
to the rear panel gain range, the input channel may be turned completely off. The current gain value of the rear
panel controls is displayed on the Input Gain tab.
Matrix crosspoint gain can be set using the Matrix tab. Input-to-output gains are set based on the requirements of
the application. The factory default matrix setting is In1 to Out1, In2 to Out2, In3 to Out3, and In4 to Out4, all at 0dB
crosspoint gain.
System equalization and feedback control are manipulated in the Filter Setup tab. The frequency response of the
sound system is adjusted with parametric filters, followed by an automatic digital feedback elimination (ADFE)
process that uses narrowband notch filters. The equalization should be set first, then several ADFE filters as follows.
Normally, several filters (2 to 4) are set to the ADFE function and deployed to notch out the worst feedback frequen-
cies in the room, and then the setup is stored into memory. Any time the setup is stored into the DSP4/4 memory or
to disk, the frequency of any ADFE filter that has been deployed will also be stored. To deploy the filter (or “ring out”
the system), gradually raise the volume of the sound system using the ADFE Setup window in the computer screen
control panel. When feedback begins to occur, the DSP4/4 will automatically detect it and set a notch filter to cancel
it. Continue to increase the volume until the next feedback frequency is detected and the next filter is deployed, and
so on. After all the designated ADFE filters have been deployed, store the settings to memory or disk to preserve
the frequency setting on each filter. These filters will then operate at these fixed frequencies every time the system is
powered up. If the volume has been increased the full 10dB allowed in the window on the screen and no further
feedback occurs, the system is likely to be very stable and not need any additional filters.