DESCRIPTION

The model VM-4024E is a four channel Voice-Matic® automatic mixer with remote control capability for input channel sensitivity, auxiliary input level, master output level, plus mode selection between automatic and standard mixer operation. Remote Control electronics are contained in the mixer and respond to DC voltage levels from a VM-209E Remote Control unit or individual remote potentiometers. Four transformer isolated automatic mixing inputs include individual switches for 24 VDC phantom power, a 14dB input pad for high output electret condenser microphones, and a 100 Hz Low-Cut filter bypass. Input #4 may be converted to line level sensitivity for use with wireless microphones and other high-output sources. All inputs and outputs are made with removable screw-clamp terminal-block connections. The microphone gating circuitry can be selected for LAST MIC HOLD. This feature enhances room ambience continuity for tape recordings, teleconferencing, hearing assistance systems, and other off premises transmissions. LAST MIC HOLD will keep the most recently activated microphone channel held to the ON status until another active input is detected.
Two electronically balanced auxiliary inputs are available for use with various line level sources. Level control for auxiliary input #1 is by a front panel knob on the VM-4024E or via remote control (from the VM-209E or from an externally mounted 100kW potentiometer). Auxiliary input #2 has a fixed gain setting of 10dB for use with CD players, cassette recorders, or other external sources which include their own output level control. Remote control of the mixer passes to the DE-209E Remote Control unit when it is connected, and returns to the DE- 4024E front panel controls when it is disconnected. The VM-4024E can be set up for unattended automatic mixing, or special events can be operator mixed by attaching the DE-209E Remote Control unit.
The DE-209E Remote Control unit is supplied with a 10' cable, terminated with an 8-pin DIN plug. This provides for a simple and rugged connection to a mating receptacle. An 8-conductor shielded cable between the VM-4024E and a wall receptacle is recommended. The 8-pin DIN plug mates with the VM-4024E mixer. Alternately, individual 100kW counter-clockwise log potentiometers (IRP P/N 105-0003) may be mounted on a custom remote control panel, one for each control, thereby eliminating the need for a DE-209E. Any combination of remote controls may be installed. Those not controlled remotely remain under front panel control. The main output is a mix of the four gated microphone signals with automatic level compensation for number of open microphones (NOM) count, plus the auxiliary inputs. The main output is used for sound reinforcement, affording feedback stability with maximum gain and minimum background noise/reverberation.
The auxiliary output is intended for tape recordings, teleconferencing, hearing assistance systems, and other off premises transmissions. The VM-4024E provides an auxiliary output mix of the gated microphone inputs and the auxiliary inputs. This unit reduces pick up of background noise/reverberation (all mic inputs gated) and depends on LAST MIC HOLD for the continuity of room ambience. Specifically for the MIX-MINUS connections to and from a teleconferencing hybrid device, the auxiliary input #1 signal may be disconnected from the auxiliary output mix.


APPLICATIONS

The Voice-Matic Microphone Mixer is ideal for use in multiple microphone sound systems installed in: Board Rooms, Court Rooms, City Council Chambers, Churches, Schools, Conference Rooms, Teleconferencing Systems, and Convention Centers. The VM-4024E automatic mixer is particularly effective in reducing the pick up of background noise that may be amplified by a sound system, or for replacing standard mixers in systems that produce feedback howl without adequately loud program sound levels. Rooms that sound reverberant with standard mixers will have much better quality and more intelligible sound with a VM-4024E Voice-Matic Mixer. There are two ways to control this mixer remotely. The DE-209E Remote Control unit provides operator control of the mixer settings from a location away from the mixer itself. When the DE-209E control unit is disconnected, the mixer returns to normal, unattended and secure operation as set by the front panel controls. Alternately, the inputs and main output of the mixer can be controlled with a potentiometer at a remote location for a customized permanent installation.


OPERATING PRINCIPLES

The Voice-Matic Microphone Mixer is unique in operating principle. It uses Dynamic Threshold Sensing (DTS) to differentiate between active and inactive microphones. DTS generates a threshold scan which starts at high levels and moves over an 80dB range to low levels. All microphone inputs are scanned simultaneously. When the DTS sensor determines which channel has the highest level, that channel is given temporary ON status. Simultaneously, the threshold is reset high and another scan initiated. On a repeated scan the same or a different channel may have the highest level and receive temporary ON status. In this way, the active microphone channels are detected and updated and maintained in an ON status. Several microphones can have simultaneous ON status and be effectively updated without dropouts. Rather than turning an inactive microphone OFF it is attenuated by an internally pre-set 12dB. The microphone is rapidly turned ON when it receives a signal, preventing upcutting of leading syllables. A continuous count of the number of ON microphones is used to adjust the master amplifier gain according to the rule of reducing gain by 3dB for each doubling of the number of simultaneously active microphones.
The mixer shall provide automatic attenuation of inactive input channels and maximum gain to active channels. Each channel shall be operated automatically and shall not be gain modulated by other input channels except as necessary to maintain feedback margin through automatic master gain reduction when simultaneously active inputs occur. A 3dB automatic master gain reduction for each doubling of simultaneously active channels is required. Channel activity shall be sensed by a dynamic threshold method. Static (fixed) threshold gating shall not be acceptable. The mixer shall be configured with 4 microphone input channels, two line level auxiliary inputs, a main sound reinforcement output and an auxiliary output specifically designed for tape/ teleconferencing/hearing assistance systems/remote premises broadcast. All outputs and microphone channel inputs shall be transformer coupled. Each microphone input shall include switched 24 VDC phantom power via the transformer center tap, a switched 14dB input pad, and a defeatable 100 Hz Low-Cut filter. One microphone input shall be switchable to accommodate line level signals from wireless microphone receivers and other line level sources. Automatic operation shall include switch selection for LAST MIC HOLD circuitry, such that the most recently activated microphone channel shall remain in the ON state until another active input is detected. One auxiliary input shall have a fixed gain of 10dB for use with line level sources incorporating internal output level controls. One auxiliary input shall have variable input sensitivity. Microphone sensitivities, the variable auxiliary input level and main output gain shall be remotely controllable by remote DC potentiometer controls over a 55dB control range. Disconnection of a remote potentiometer shall return control to the corresponding front panel control. A remote control unit shall be provided. Connection of the remote control unit shall cause control of input channel sensitivities, one auxiliary input level, master output level and mixer mode selection to be at the remote control unit. Disconnection of the remote control unit shall return the mixer to the control settings on the front panel.
The auxiliary output shall have a rear panel level control. The mix to the auxiliary output shall include the four gated microphone signals plus the auxiliary inputs. The auxiliary input with variable sensitivity shall be defeatable from the mix to the auxiliary output in order to provide the correct MIX-MINUS signal connections to a teleconferencing hybrid device through this auxiliary input and output.
The front panel shall have sensitivity controls for the microphone inputs and variable auxiliary input, master output level, plus LED™s for microphone status indication. The rear panel shall have removable screw-clamp terminal-block connectors for the inputs and outputs, a screwdriver auxiliary output level control, an 8 pin DIN socket for remote control connections; individual microphone channel switches for phantom power, input pad, and low-cut filter; plus switches for Automatic/Standard mixing mode selection, LAST MIC HOLD operation, MIX-MINUS of the variable auxiliary input to the auxiliary output mix, and Mic/Line selection for one automatic channel input. The automatic mixer shall be the IRP model VM-4024E four channel Voice-Matic Mixer.
The Remote Control unit shall provide sensitivity controls for the microphone inputs and variable auxiliary input, master output level, plus switch selection between Automatic and Standard mode of mixer operation. The Remote Control unit shall provide 55 decibels of level adjustment range. A 10 foot cable from the Remote Control unit shall be terminated in an 8 pin DIN plug for connection to the mixer. Insertion of this plug to the mixer socket shall transfer all the respective mixer controls to the Remote Control unit. Disconnection of the Remote Control unit shall cause control to be at the mixer front panel. The Remote Control unit shall be the IRP model DE-209E.