Here you can find answers to various often asked questions about MIDI. How does it work, regularly used terminology, study cases, MIDI Boutique customer experience.

MIDI Boutique

WHAT IS...

Below you can find the answers of the most common questions concerning our units. All definitions are given in context of MIDI encoders/decoders and may not be appliccable to other subjects of human knowledge.

• What is SCANMATRIX/SCANPOINT ?

  SCANMATRIX is key contact arrangement allowing scanning of multiple key contacts using minimal wiring. The contacts in scanmatrix are also refered to as SCANPOINTS. Scanmatrix requires grouping of keys, most typically in groups of 8, with all contacts in group having common terminal. These groups are also called COLUMNS. The other terminal of contacts are wired as follows: all contacts placed at first position in the groups are wired together to ROW1, all contacts placed at second position are wired together, forming ROW2 etc. In most typical 8x8 scanmatrix, there are 8 rows and 8 columns. Note that it is absolutely necessary to put single diode (1N4149 or similar) serially with each contact. The diode may reside both above and or below the contact (by schematic diagram). If diodes are missed, the scanner/encoder won't be able to tell the column of currently scanned key contact, and will output wrong MIDI messages.The schematic of 8x8 scanmatrix arrangement is shown below. Note that the whole set of 64 keys needs all in all 8+8=16 wires to connect to external world. Also note that there are two types of scanmatrices: common anode and common cathode. The difference between these types is in key indexing. Per example, Key#3 will reside on Row#, Col#3 in common cathode matrix, and the same Key#3 will reside on Row#3, Col#1 in common anode matrix. Therefore, the encoder should be designed (set) for the right type of scanmatrix, to be able to scan/interpret keys in right order.

• What is MATRIX SCANNING SYSTEM ?

This is system where you have wired together an matrix-organized key contact system and scanmatrix encoder unit. The connection between these parts is more than simple. They are connected via 8+8 = 16 wires, usually 2 ribbon cables, each of 8 wires. The schematic below illustrates a system where an commn-cathode scsanmatix takes place.

• What is SCANROW ?
  
  In contast to Scanmatrix, SCANROW is key contact organinzation where all key contacts have one common terminal. The wire going thru upper (by schematic) terminals is also called BUSSBAR. The other terminal of each key contact is wired separately to the external worls. Therefore1+64 wires are needed for connecting 64 key contacts to external world. Note that diodes are not necessary in this type of organization.

• What is ROW SCANNING SYSTEM ?

System where you have wired together an scanrow-organized key contact system to scanrow (also called parallel) scanner-encoder unit. The connection between these parts requires many wires, which may be problem in big systems.

• SCANMATRIX versus SCANROW

• SCANMATRIX pro's:
  • minimal wiring for external connections
  • cheap and small-sized encoders
• SCANMATRIX con's:
• requires diode per each contact
• requires cutting existing bussbar into pieces

• SCANROW pro's:
• easy implemented in existing old keyboard instruments where bussbar is widely used
• does not require additional elements like diodes
• SCANROW con's:
• needs too many wires (keys + 1) for connecting to external system
• parallel encoders that may be used for scanning such keyboards are more expensive and big in size
• in case a cheap matrix encoder is available, it cannot be used directly with SCANROW. Additional key multiplexor unit is required for this.

• What is KEYMULTIPLEXOR ?
  
  
  If existing keyboard system, of scanrow (bussbar) organization has to be turned into MIDI instrument without re-arranging its organization, and scanmatrix encoder is used, an additional unit called KEYMULTIPLEXOR is required, inserted between the keyboard scanrow and scanmatrix encoder. Since the keyrow has many output wires, and matrix encoder has few inputs, the KEYMULTIPLEXOR transforms the parallel data coming from keyboard to matryx-data, required by the encoder. Since the most of encoders we offer are of matrix type, the KEYMULTIPLEXOR could be an easy way to fit our MIDI encoders to existing keyboards without re-arranging them, and at the same time using minimized number of wires between the keyboard and encoder. KEYMULTIPLEXOR usually is close to the keyboard contacts, even wired directly to them. The rest of connections are done using ribbon cables, each consisting of 8 wires.

• What is Stop Action Magnet (SAM) switch ?
  
  
  SAM switches are normal toggle switches that are motorized by means of two small solenoids. SAMs are widely used in organs. They can be operated manually, by the organ player, but can also be controlled by organ's electronic on recalling memorized presets of stops. Below are pictures of most typical SAM switch, manufactured by Syndyne corp.

 

• What is Reed contact ?
  
  
  Reed contact is an hermetically sealed contact actuated by magnetic field. It is very robust against dust and humidity which are serious problem for any contact system. Reed contact are widely used in keyboards, especially in pedalboard where there is a room enough for actuating magnets. The actuating magnet can be of various shape and size. The typical Reed contact used in keyboards/pedalboards is 20 x 3 mm in size (terminals not included). Both Reed contact and actuating magnet are shown on picture below. The size of magnet shown is 20 x 10 x 5 mm.

What is the difference between active and passive keying is?

With passive (GND) keying the busbar is supposed to be connected to common/GND/0V line of keyer.
The keying voltage of +5V is supplied by keyer inputs and they sense High-Low 
transition of input upon make and Low-High transition upon break.

With active (for example +12V) the busbar is connected to +12V keying voltage source inside console. 
The GND line of keyer must be connected to GND line of console (they must have common ground).
The +12V keying voltage is applied to keyer inputs by busbar via key contacts. 
The keyer inputs are internaly pulled down to GND (0V). 
They sense Low-High transition upon make and High-Low transition upon break. 

What are Program Change, Control Change, NoteOn, NoteOff messages?

In most typical case all console buttons and switches are expected to transmit NoteOn/NoteOff messages report their position change.

Hauptwerk receives these messages and interprets them according to its configuration as done by user.

For example, notes on channel#1 are interpreted as Manual#1 keys produce sound, notes on chanel#2 - as Manual#2 keys and produce sound, notes on chanel#3 - as Pedalboard keys and produce sound, notes on channel#4 - as Stops. These don't produce sound directly, instead they switch On/Off proper stops/registers to change sound type, according to currently loaded sample sets.

 

Program Change messages are used for recalling presets of stops (programs).

That is, user can have number of pre-programmed presets each of which contains combination of various stops and can activate such a combination by simple piston, sending Program Change message.

Normally only one program/preset can take place at a time, that is why there is no ON/OFF for this kind of messages. Program Change messages are used as selector one-of-many.

They consist of Status byte followed by single Data byte, carrying only Program Number to command Hauptwerk which program/preset to engage.

 

A Control Change consists of three bytes: Status (first) byte, presenting message type (CC) and MIDI channel (0..15), Data1 (second) byte, presenting controller number (0..127) and Data2 (third) byte, presenting the controller value (0..127).

Each change of particular potentiometer position would cause the MIDI encoder to send of Continuous Control message carrying same Status and Data1 bytes and Data2 byte reflecting potentiometer position (0..127).

Upon receiving this message, the listening device knows that the potentiometer position has changed and the particular parameter it controls (for example CC#7-Volume) must be changed accordingly.

What type are the most commonly used key contacts/switches?

- Silver-coated springs and bars. This is the old fashioned dry-contact system which is relatively simple to build but is not reliable as it is sensitive to dust and humidity.

- Magnetically operated reed contacts. These are a bit more difficult to adjust (they are packaged in glass and are very fragile and each time when you try to bend their terminals you may break the glass). But once installed and properly adjusted they are much more reliable than any other kind of switches.

- Magnetically operated Hall switches. These are electronic switches sensitive to magnetic field similar to Reed switches. But being electronic devices they need additional power supply to operate. This may be problem with battery-operated instruments or with instruments powered from USB as in both cases the power is limited. Apart from this these are very reliable.

- Optical switches. These need even more current than Hall switches as their LEDs must be powered all the time, unless a clever electronic system is used for dynamically switching them on and off. They are sensitive to dust and considering both power and dust factor I'd reject them.

What is the difference between mkc64x/mpc32xrs/mpc32mq MIDI encoders?

Mkc64x is scanmatrix encoder. It requires that contacts are wired in scanmatrix (in groups of 8, with diodes in series with each contact, having local common line per group. The 8x8 scanmatrix is terminated at 16-pin header. 

Mpc32xrs and mpc32mq are scanrow encoders. They require separate wire per key plus one common for al keyc. No diodes ar necessary. A scanrow encoder is normally terminated at N+2 pin header (where N is the number of key inputs). Therefore mpc32 encoders are terminated at 34-pin headers and have 32 key inputs.

Mpc32mq is the successor/upgrade of mpc32xrs. It has many advantages compared with its predecessor like:

- MIDI Merge input;

- 4 analog input for potentiometers (swell, volume etc. pedals or faders);

- 8 additional inputs for switches (pistons);

- Much more parameters available to user to set.

Reed switch or Hall effect contact system to choose? Pros and Cons.

There is no functional difference between Reed and Hall contacts. The difference is in their reliability. Reed contacts are electromechanical, made of glass, therefore they are very fragile and have limited number of contact makes. Hall contacts are more reliable, theoretically have unlimited number of makes, but require power. The power is distributed by mpc32mq MIDI encoder (If you want to use this contact system with other encoder, please check for the compatibility).

Although reed contacts are extremely fragile and relatively difficult to adjust, they have best price/quality ratio. The big advantage of Hall switches is that they are not fragile and there are no moving parts inside. 

MIDI Boutique offering contact systems with two types of contacts organization (designes) – individual contacts attached directly on a wire and contacts mounted on a solid PCB. 

This solution is very reliable for the reed contacts because they are in more secure position during installation and use.

Customer should keep in mind that these designes with contacts mounted in groups on a long PCB may not fit good on some rounded shape pedalboards. If you have such, we recommend you consider a contact system with individual contacts.