MIDI Protocol

All the physical controls of the Controller Deck (faders, knobs, buttons, pads and the TouchDeck grid) are reported to the host as standard USB MIDI events. The device also accepts MIDI messages sent by the host to control the buttons/knobs levels and their RGB backlight, or to configure the touchscreens widgets.

USB device identification

The MIDI interface is exposed on the main TouchDeck USB device:

Field	Value
bcdUSB	2.00 High Speed
Vendor ID	`0xFFFF`
Product ID	`0x1234`
iManufacturer	LambdaConcept
iProduct	TouchDeck

USB Descriptor details …

Bus 001 Device 092: ID ffff:1234 LambdaConcept TouchDeck
Negotiated speed: High Speed (480Mbps)
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            0 [unknown]
  bDeviceSubClass         0 [unknown]
  bDeviceProtocol         0
  bMaxPacketSize0        64
  idVendor           0xffff LambdaConcept
  idProduct          0x1234 TouchDeck
  bcdDevice            1.05
  iManufacturer           1 LambdaConcept
  iProduct                2 TouchDeck
  iSerial                 3 00000000
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength       0x006c
    bNumInterfaces          2
    bConfigurationValue     1
    iConfiguration          0
    bmAttributes         0x80
      (Bus Powered)
    MaxPower              500mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           2
      bInterfaceClass         1 Audio
      bInterfaceSubClass      3 MIDI Streaming
      bInterfaceProtocol      0
      iInterface              0
      MIDIStreaming Interface Descriptor:
        bLength                 7
        bDescriptorType        36
        bDescriptorSubtype      1 (HEADER)
        bcdADC               1.00
        wTotalLength       0x0043
      MIDIStreaming Interface Descriptor:
        bLength                 6
        bDescriptorType        36
        bDescriptorSubtype      2 (MIDI_IN_JACK)
        bJackType               1 Embedded
        bJackID                 1
        iJack                   4 Grid
      MIDIStreaming Interface Descriptor:
        bLength                 6
        bDescriptorType        36
        bDescriptorSubtype      2 (MIDI_IN_JACK)
        bJackType               1 Embedded
        bJackID                 3
        iJack                   5 Controller
      MIDIStreaming Interface Descriptor:
        bLength                 9
        bDescriptorType        36
        bDescriptorSubtype      3 (MIDI_OUT_JACK)
        bJackType               1 Embedded
        bJackID                 2
        bNrInputPins            1
        baSourceID( 0)          1
        BaSourcePin( 0)         1
        iJack                   4 Grid
      MIDIStreaming Interface Descriptor:
        bLength                 9
        bDescriptorType        36
        bDescriptorSubtype      3 (MIDI_OUT_JACK)
        bJackType               1 Embedded
        bJackID                 4
        bNrInputPins            1
        baSourceID( 0)          3
        BaSourcePin( 0)         1
        iJack                   5 Controller
      Endpoint Descriptor:
        bLength                 9
        bDescriptorType         5
        bEndpointAddress     0x01  EP 1 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
        bRefresh                0
        bSynchAddress           0
        MIDIStreaming Endpoint Descriptor:
          bLength                 6
          bDescriptorType        37
          bDescriptorSubtype      1 (Invalid)
          bNumEmbMIDIJack         2
          baAssocJackID( 0)       1
          baAssocJackID( 1)       3
      Endpoint Descriptor:
        bLength                 9
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
        bRefresh                0
        bSynchAddress           0
        MIDIStreaming Endpoint Descriptor:
          bLength                 6
          bDescriptorType        37
          bDescriptorSubtype      1 (Invalid)
          bNumEmbMIDIJack         2
          baAssocJackID( 0)       2
          baAssocJackID( 1)       4
    Interface Descriptor:
      [... Custom bulk interface ...]

USB MIDI interface

The Controller Deck enumerates as a standard USB Audio Class 1.0 MIDI streaming interface (Interface 0), exposing two independent MIDI jacks:

bInterfaceNumber	bNumEndpoints	bInterfaceClass	bInterfaceSubClass	bInterfaceProtocol
0	2	Audio	MIDI Streaming	0

This interface offers one bidirectional endpoint for MIDI communication with the host.

Endpoint	Direction	Purpose
1	IN/OUT	MIDI Streaming

Jack index	Name	Content
0	TouchDeck Grid	Events and LED control for the 40-button TouchDeck grid.
1	TouchDeck Controller	Events and LED control for every other control: faders, knobs, A/B - B/S buttons, pad buttons, control buttons and the widgets touchscreens (SysEx).

Manufacturer name reported by the device: LambdaConcept.

View MIDI Devices

USB-MIDI packet format

Every event, in either direction, is carried using the standard 4-byte USB-MIDI packet format:

Byte number	00	01	02	03
Description	Cable Number \| Code Index Number (CIN)	MIDI status byte	MIDI data byte 1	MIDI data byte 2
	Cable Number: (`0` = Grid, `1` = Controller).	Message type \| Channel	Note	Velocity / Value

CIN	Message
0x8	Note Off
0x9	Note On
0xB	Control Change
0x4	SysEx starts or continues (3 data bytes follow)
0x5 / 0x6 / 0x7	SysEx ends with 1 / 2 / 3 data bytes

Control mapping

Every physical control group is mapped to a range of MIDI note numbers or controller (CC) numbers, all on channel 0. Groups that have a backlight also report a led_channel, which is the MIDI channel to use when sending LED color/mode messages back to the device (see LED color control below).

Control	Jack	Message	Range	LED channel
TouchDeck grid (40 buttons)	Grid (0)	Note On / Note Off	0-39	0
RGB knobs	Controller (1)	Control Change	0-9	1
Knobs	Controller (1)	Control Change	10-20	–
Faders	Controller (1)	Control Change	21-31	–
A/B - B/S buttons	Controller (1)	Control Change	32-51	1
Pad button + Control buttons (x2, /2, TAP, RESYNC)	Controller (1)	Control Change	72-85	1
Touchscreens widgets	Controller (1)	Control Change	86-127	–

Event examples

The following examples show the raw 4-byte USB-MIDI packet produced by the device when a control is used.

Event	Packet (hex)	Description
Grid button 5 pressed	`09 90 05 7F`	Cable 0 (Grid), Note On, channel 0, note 5, velocity 127
Grid button 5 released	`08 80 05 00`	Cable 0 (Grid), Note Off, channel 0, note 5, velocity 0
RGB knob #0 (`kla`) turned	`1B B0 00 40`	Cable 1 (Controller), CC, channel 0, controller 0, value 64
Knob #0 (`knr`, CC 10) turned	`1B B0 0A 64`	Cable 1 (Controller), CC, channel 0, controller 10, value 100
Fader #0 (`fdr`, CC 21) moved	`1B B0 15 7F`	Cable 1 (Controller), CC, channel 0, controller 21, value 127
A/B button (`bsr`, CC 32) pressed	`1B B0 20 7F`	Cable 1 (Controller), CC, channel 0, controller 32, value 127
Pad button (`bpa`, CC 72) pressed	`1B B0 48 7F`	Cable 1 (Controller), CC, channel 0, controller 72, value 127
`TAP` control button (`drt`, CC 86) pressed	`1B B0 56 7F`	Cable 1 (Controller), CC, channel 0, controller 86, value 127

LED color control

The RGB backlight of the TouchDeck grid buttons (grid), RGB knobs (kla), A/B - B/S buttons (bsr) and pad buttons (bpa) is controlled by sending a Note On message to the device, on the led_channel given in the mapping table above.

Field	Meaning
Message	Note On
Note	Button/knob index (0-39)
Velocity bits [0:4]	Palette color index (0-31)
Velocity bits [5:6]	Mode

Mode value	Mode
0	SOLID
1	BLINKING
2	FADING
3	TURNING

The velocity byte is therefore computed as (mode << 5) | color_index.

32 colors palette

Idx	RRGGBB	Idx	RRGGBB	Idx	RRGGBB
0	`0x000000`	1	`0x000000`	2	`0x000000`
3	`0x000000`	4	`0x505050`	5	`0xFFFFFF`
6	`0x7F2626`	7	`0xFF0000`	8	`0x803713`
9	`0xFF2A00`	10	`0x7F5226`	11	`0xFF7F00`
12	`0x7F7F26`	13	`0xFFFF00`	14	`0x527F26`
15	`0x7FFF00`	16	`0x267F26`	17	`0x00FF00`
18	`0x267F44`	19	`0x00FF55`	20	`0x267F7F`
21	`0x00FFFF`	22	`0x26437F`	23	`0x0054FF`
24	`0x26267F`	25	`0x0000FF`	26	`0x874CFF`
27	`0x5400FF`	28	`0x7F2661`	29	`0xFF00AA`
30	`0x7F2635`	31	`0xFF002A`

LED example

Set grid button 5 to solid red (palette index 7, mode SOLID = 0):

velocity = (SOLID << 5) | 7 = (0 << 5) | 7 = 0x07

Packet: 09 90 05 07
         |  |  |  |
         |  |  |  +-- velocity: color index 7 (red), mode SOLID
         |  |  +----- note: button index 5
         |  +-------- Note On, channel 0
         +----------- Cable 0 (Grid), CIN 0x9 (Note On)

Set A/B button, relative index 0 within the bsr range, to fading cyan (palette index 20, mode FADING = 2), on the bsr LED channel (1):

velocity = (FADING << 5) | 20 = (2 << 5) | 20 = 0x54

Packet: 19 91 00 54

Sending LED / MIDI messages via the control endpoint

If the standard MIDI interface is already claimed by other software, the same 4-byte USB-MIDI packet can also be delivered to the device through a vendor control transfer, “Set MIDI” (request 5), on the control endpoint (see Icons Protocol for the full list of vendor requests):

Field	Value	Computed from packet `[b0, b1, b2, b3]`
bRequest	5	–
wIndex	`(b0 << 8) \| b1`	Cable/CIN byte and status byte
wValue	`(b2 << 8) \| b3`	Data byte 1 and data byte 2

Example, using the same “grid button 5 solid red” packet (09 90 05 07) as above:

wIndex = (0x09 << 8) | 0x90 = 0x0990
wValue = (0x05 << 8) | 0x07 = 0x0507

async setCustomMIDI(device, midi32) {
    const value = (midi32[2] << 8) | midi32[3];
    const index = (midi32[0] << 8) | midi32[1];
    await device.controlTransferOut({
        requestType: "vendor",
        recipient: "device",
        request: 5,
        value: value,
        index: index,
    }, new Uint8Array(0));
}

Touchscreens widgets (SysEx)

The two round touchscreens are configured with SysEx messages sent on the Controller jack (jack index 1). SysEx payloads longer than 3 bytes are split across several USB-MIDI packets, using CIN 0x4 for the bytes that start/continue the message and CIN 0x5/0x6/0x7 for the packet that ends it with 1, 2 or 3 bytes respectively.

Command	SysEx (hex)	Purpose
`touchscreen_widget`	`F0 7D 00 01 02 F7`	Assign a widget (e.g. crossfader, color picker) to a touchscreen.
`touchscreen_brightness`	`F0 7D 01 7F F7`	Set the touchscreen backlight brightness.
`touchscreen_mirror`	`F0 7D 7E 01 01 F7`	Mirror the touchscreen content.
`touchscreen_factory`	`F0 7D 7F 01 F7`	Restore factory settings for the touchscreen.

Example – USB-MIDI packet breakdown for touchscreen_brightness (F0 7D 01 7F F7, 5 bytes, sent on Cable 1):

Packet 1: 14 F0 7D 01   (CIN 0x4: SysEx starts/continues, 3 bytes: F0 7D 01)
Packet 2: 16 7F F7 00   (CIN 0x6: SysEx ends with 2 bytes: 7F F7, byte 3 unused)

Example – USB-MIDI packet breakdown for touchscreen_widget (F0 7D 00 01 02 F7, 6 bytes, sent on Cable 1):

Packet 1: 14 F0 7D 00   (CIN 0x4: SysEx starts/continues, 3 bytes: F0 7D 00)
Packet 2: 17 01 02 F7   (CIN 0x7: SysEx ends with 3 bytes: 01 02 F7)