Since MIDusb-midi-cable-5I was developed, connecting any music gear via this system has proven to be one of the most amazing things the community has witnessed. The myriad of devices that have been possible to connect and be controlled, it is remarkable!

Imagine that is possible for a Drum to control and select the sound and FXs that a Guitar plays with?  And ever wondered how a Keyboard could dim the lights on a stage, in real time? It enables to keep the beat synchronized on all devices, change programs, channels, pitch, volume, you name it. Everything by done automatically by the devices or, if connected, a computer.

Having a computer connected to the MIDI network of the instruments or devices opens up a new world. Yes, MIDI brought us many possibilities and

opportunities. But also it raised other issues that have been neglected or simply discarded or even not noticed in some instances.

Due to the fact that we now use a cable to control our instruments or devices, leaves the door open to all possible noisy complications, situations that may cause havoc on our system and sound extracted-produced thereof.

The developers of the MIDI system/protocol did a very neat thing that greatly guaranteed the performance in almost all situations: it uses a current loop instead of voltage levels. This is most clever because it eliminates the erratic behaviour a system controlled by voltage levels has when exposed to the noisy environment of a live stage.

Although the current loop greatly improves the system, there are still a few issues that undermine it and cause problems when in live situations or studio recordings.

1.   The MIDI Transmitter does not have enough power

The MIDI transmitter is not powerful enough to drive the MIDI receiver.

One of the reasons may be an intrinsic higher line impedance or a temporary increase in the signal line impedance due to change in the conditions or by using new cables. A higher impedance in the line means that the current needed by the receiver to proper bias the optocoupler, is not enough. And an improper biased optocoupler may swing the output randomly with changes in ambient temperature and in the output pull-up voltage.

Another reason is the Transmitter itself that is, by design, not energetic enough to properly drive the signal line, even if the conditions are optimal. When adding layers of protection and security to the transmitter output, some designs lose some power.

The solutions to this problem go by opening the equipment and changing the electronic circuitry on the output stage of the transmitter and/or the input stage of the receiver. This is a tricky one and not straight forward for someone who is not experienced in electronics.

The other solution is using a MIDI Buffer Isolator, that will take the transmitter signal, amplify/buffer it, clean it and provides a true isolation between input/output – transmitter/receiver.

2.   The MIDI cable is longcable_reel

As seen in the previous paragraph, an increase in line impedance may change dramatically the conditions on how the transmitter and receiver operate.

Electric cables are usually made of Copper. This metallic element is a very good electric conductor but as with all the metals, it is not perfect. Its resistance increases with length and the longer the cable the higher its resistance. Wire cross section is also important because it reduces metal area in the wire, hence increasing resistance.

Reducing the length of the MIDI cable may not be possible thus the solution here is again using a MIDI Buffer Isolator.

3.   EMI / RFI issues

Electromagnetic InEMI_cables_Analog_digitalterference or Radio Frequency Interference are two very common causes in today’s day and age. With the increase in wireless devices, switched power supplies and electronic devices altogether, the ether around us is saturated with radio waves and even more radio interference generated by all this electronics pushing electrons.

One of the most important steps to mitigate EMI in our musical or control systems is to shield our devices and cables properly. A proper installed shield can completely clean our unexpectedly dirty systems and save the day in a live gig or recording studio.

EMI affect and deteriorate signals transmitted along an unshielded cable. A disturbed signal leads to dropped packets in the MIDI line and consequent poor system performance and a compromise in quality.

Solutions for this are the following:Homemade_balun

  • Use a good quality shielded cable
  • Cable shield must be connected on the transmitter equipment . To make sure of this, one has to open both transmitter and receiver and check how the DIN sockets are connected. Pin 2 on the transmitter must be connected to shield, and pin 2 of the receiver must be disconnected
  • Wind the MIDI cable to a toroidal ferrite like the one below. Do it at the transmitter and especially at the receiver
  • Use a MIDI Buffer Isolator that will filter the noise at the input and will send clean strong signals to the outputs
4.   Ground Loops

Ground loops happen when electric grounds are connected together with no defined star point and hence in rings. Ground ring connections are disastrous to sound and control systems. They lead to that traditional “hum” and a very noticeable loss of MIDI packets.

The ground loops causes return currents to go through the device that has the least ground impedance and may not necessarily be the originating one thus causing these problems. In the digital domain, where MIDI seats,  the difference is by changing the ground reference levels between systems. This means that if we would measure ground voltage, it would fluctuate from 0V to negative or positive values. This  garbles the receiver, especially if the ground goes more positive thus reducing the magnitude of the signal.

Solutions for this are the following:

  • Use a good quality shielded cable
  • Cable shield must be connected on the transmitter equipment . To make sure of this, one has to open both transmitter and receiver and check how the DIN sockets are connected. Pin 2 on the transmitter must be connected to shield, and pin 2 of the receiver must be disconnected
  • Use a MIDI Buffer Isolator that will provide galvanic isolation (no electrical contact) between input-output and amplifies the output signal

 

What are your thoughts about this matter? I invite you to leave a comment.