Philip Rees MIDI line driver systems overcome the distance restriction (officially 15 metres maximum) of the standard MIDI hardware. They convey a MIDI datastream over long cable runs by converting to and from a robust differential (balanced) signal format. We make two types of long distance MIDI Line driver system, the widely-used high-performance MLD, and the useful bi-directional MTR.
MTR Bidirectional MIDI Line Driver TheMTR MIDI Line Transmitter/Receiver offers a full duplex solution for MIDI communication over cable runs of up to 150m. This product does not feature waveform restitution.
MTR consists of a pair of units, each of which is a dinky 109mm x 55mm x 40mm. The cable link between the two units is made via four or five conductors, two screened twisted pairs would be ideal. The connections to the line cable are via 240 degree 5 pin DIN plugs, which are supplied.
Applications Remember, the MTR is particularly useful where no mains power is conveniently available at the remote end of the line.
In live music applications, the MTR can allow interaction between MIDI equipment on the stage and at the desk. The MTR can work down multicore and has many uses in live sequencing and automation.
MIDI-based show control systems may be installed in theatres. For example, MIDI may be used to control lighting or to transfer triggers from the stage to automatically cue sound effects. These situations require the ability to get MIDI data down long cable runs.
In recording studios, particularly with remotely located control rooms, an MTR system can be part of the permanent installation. They can also be used on an ad hoc basis, with the remote unit employed rather like a DI box.
MLD MIDI Line Driver MLD allows the signal to traverse cable runs of up to a kilometre with quality screened twisted pair (STP) cable. Unscreened cable can also be used.
The MLD system consists of a pair of units. MLD/T is a transmitter unit with a built-in mains (ac) power supply and integral mains lead (ac power cord) fitted with a plug. A POWER lamp indicates that the MLD/T is powered-up. A DATA lamp flashes clearly to indicate that that MIDI data is passing through.
As with all our ac-powered products, versions are available for 110 V ac as well as 230 V ac. Power plugs for various international standards are also available.
The MLD/R receiver unit is phantom-powered over the line. The case of each unit are 109mm x 55mm x 40mm. The connection to the line cable is via 240 degree 5 pin DIN plugs, which are supplied.
Technical refinements MIDI-thru chains can distort the MIDI waveforms. So that the line driver is sure to receive a clean signal, the MLD/T unit includes our fast, high -precision "Cleanstream" waveform restitution. This processing is applied to the MIDI-thru output and the line output. Because this processing ensures that the duty cycle of the waveform is perfect, it also helps to make sure that the MLD system can convey a signal over the full specified distance. The "Cleanstream" process has a 250ns sample period, so it is many times more discriminating than ordinary serial interfaces.
The differential LINE cable connections are made via 240 degree 5 pin DIN plugs and sockets.
In the receiver unit, a low pass filter followed by hysteresis provide amazingly reliable performance, even in electrically noisy environments. Hysteresis is the method where the threshold level of a signal detector changes depending on the previous state of the signal; it is employed to enhance noise immunity. Many applications
In live performance situations, the MLD can allow on-stage MIDI gear to be controlled from the desk. Alternatively, the MLD can transmit performance data back to modules located at the desk end.
MIDI-based systems installed in theatres may require the ability to get MIDI data down long cable runs reliably. The MLD system can do this.
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