In general, Windows MIDI Services translates MIDI messages only when it absolutely has to (primarily to support MIDI 1.0 devices or MIDI 1.0 APIs). This translation happens in different places, depending upon the driver in use.
Internally, the MIDI service moves messages around in the UMP format. This enables a standard format for message scheduling and processing. In addition, the Microsoft.Windows.Devices.Midi2* SDK and the service behind it, both treat all messages as UMP, including ones to/from devices which were MIDI 1.0 byte data format.
This is the byte format (also called “byte stream” due to how it operates over MIDI 1.0 DIN/Serial connections) used by MIDI 1.0.
This is the Universal MIDI Packet format. Packets are from 1 to 4 32-bit words in length, and are self-contained and atomic. Internally in Windows MIDI Services, all messages are processed and transports in UMP format, and translated to MIDI 1.0 byte data format as needed
The MIDI messages defined in the MIDI 1.0 specifications, with most values between 0-127, and messages containing 1-3 bytes (except System Exclusive). These messages can be transported in the MIDI 1.0 data format, or in the Universal MIDI Packet format.
The MIDI messages defined in the MIDI 2.0 UMP specifications, excluding the MIDI 1.0 protocol messages in UMP format.
Windows MIDI Services supports both MIDI 1.0 and MIDI 2.0 devices.
| Device | Driver | Microsoft.Windows.Devices.Midi2 | WinMM/WinRT MIDI 1.0 APIs |
|---|---|---|---|
| USB MIDI 1.0 Device | MIDI 2.0 Class Driver | To/From MIDI 1.0 in UMP by driver | To/from MIDI 1.0 byte data format by service |
| USB MIDI 1.0 Device | Older MIDI 1.0 Class Driver | To/From MIDI 1.0 in UMP by service | To/from MIDI 1.0 byte data format by service |
| USB MIDI 1.0 Device | Vendor MIDI 1.0 driver | To/From UMP by service | To/From MIDI 1.0 byte data format by service |
| USB MIDI 2.0 Device | MIDI 2.0 Class Driver | No translation required | To/from MIDI 1.0 byte data format by service |
| Any other MIDI 2.0 Device | (no driver. ex Virtual, Network 2.0) | No translation required | To/from MIDI 1.0 byte data format by service |
| Any other MIDI 1.0 Device | (no driver. ex BLE) | To/From UMP by service | To/From MIDI 1.0 byte data format by service |
Incoming messages are translated between protocol and data format only when necessary, as explained above.
WinMM and WinRT MIDI 1.0 will always receive correct MIDI 1.0 channel voice messages, no matter what the endpoint has.
Microsoft.Windows.Devices.Midi2 will provide the UMP version of what it is provided. It does not upscale MIDI 1.0 channel voice messages to MIDI 2.0 channel voice messages. The client may use open source libraries to handle that if needed.
Currently, Windows MIDI Services does not translate messages based on Function Block declared protocol. Instead, for native UMP endpoints, applications should send the correct protocol messages (message type 2 for MIDI 1.0-compatible and message type 4 for MIDI 2.0-compatible messages) based upon the information provided by the MidiEndpointDeviceInformation class. In addition, for native MIDI 1.0 byte data format endpoints, applications should send the appropriate MIDI 1.0 messages in UMP.
Windows MIDI Services will downscale messages as needed based on endpoint negotiated protocol. We plan to add MIDI 1 -> MIDI 2upscaling (if an endpoint negotiates MIDI 2 but doesn’t support MIDI 1), but that is not in place in the first release.
If a MIDI 1.0 device is connected to the new MIDI 2.0 Class Driver, Windows MIDI Services will downscale Message Type 4 to Message Type 2 before sending to the driver. This is because the driver, when working with a MIDI 1.0 device, only handles UMP messages which can be directly translated to MIDI 1.0 data format.
As mentioned above, Windows MIDI Services does not filter out or translate messages based on the declared protocol. Applications should use the Function Block (preferred) or Group Terminal Block (backup) data to decide which protocol to use when sending messages. However, Windows will not stop an application from sending a MIDI 2.0 Protocol in UMP message to a Group in a Function Block which specifies MIDI 1.0 Protocol.
To learn more about metadata like Function Blocks, see the section on Enumerating endpoints.
Windows MIDI Services does not, by default, translate a MIDI 1.0 Note On with zero velocity to a MIDI 1.0 Note Off message. Doing so would break the Mackie protocol and possibly others.
When translating between MIDI 2.0 Protocol in UMP and MIDI 1.0 protocol (MIDI 1.0 byte data format, or MIDI 1.0 protocol in UMP), Windows MIDI Services follows the MIDI 2.0 UMP specification and translates a MIDI 1.0 Note On with a zero velocity to a MIDI 2.0 Note On with a velocity of 1. However, there is no code, outside of the SDK helper functions, which does this today, as incoming MIDI 1.0 byte data format messages are always translated into MIDI 1.0 protocol in UMP. We do, however, downscale MIDI 2.0 Protocol in UMP to MIDI 1.0 byte data format when required, as per above.
Windows MIDI Services makes use of publicly-available open source libraries for protocol and data format translation.
Windows MIDI Services is an open source project with all source available on GitHub. We have a great community on Discord as well. Between GitHub and Discord, you should find the information you are looking for.
