PreSonus StudioLive 16.0.2 USB Reverse Engineering

This documentation is work-in-progress and provided as-is.
I tried to optimize for information-density while still retaining some kind of clarity.
Thus, some things might only make sense if you're already familiar with this mixer / USB in general.
I hope it's helpful nonetheless.

USB Protocol

Through looking at the USB traffic captured by Wireshark, while fiddling with the mixer controls / Universal Control PC software, I made the following conclusions:

Request

The Universal Control application sends commands to the mixer via vendor defined USB control requests on endpoint 3.
They follow the pattern F0 <command> F7.

Response

• Starts with 04 or 07 depending on the length of the following payload (see "chunking" below)
• Always ends in F7 (sometimes there are a few null bytes after the last byte though).
• Appears to have some kind of chunking.
  • The chunks are 4 bytes in length.
  • The first byte is the chunk flags (?) followed by 3 data bytes.
  • Chunk flags (bitfield): 04: always set, 02: last chunk, 01: single chunk?
• (It seems to repeat the same message without chunking on endpoint 4?)
• Many values seem to follow some kind of split-nibble encoding.
  The actual value of e.g. AB gets transferred as 0A 0B.

Commands

38 03 General Status Request?

This request gets sent periodically roughly every 40ms.

Response:

Offset	Example	Description
00	39 03	Command (but 0x39)
02	00	?
03	00	Selected Channel
...
10	00 08 01 00	Channel State Changed Notification Bitfield: 00 00 00 01: Ch1 00 00 00 02: Ch2 00 00 00 04: Ch3 00 00 00 08: Ch4 00 00 01 00: Ch5 ...
14	00	01: FXA State Changed (=> 6D 03 00)
15	00	01: FXB State Changed (=> 6D 03 01)
16	00	01: GEQ State Changed (=> 6D 01)
17	00	01: Fader Positions Changed (=> 6E)
18	00	01: System Settings Changed (=> 60)
...
21-33	01	Channel Level Meters Min: 01, Max: 21
34-41	01	More Level Meters?
42	01 01	Main Level Meter (L/R)
44	1E	?

53 MIDI Control Write

See below

54 MIDI Control Read

MIDI Settings in the "System" page

MIDI channels 1-16 are transferred as 00-0F. MIDI control channels 0-127 are transferred as 00 00 - 07 0F (see split-nibble).

Response:

Offset	Example	Description
00	54	Command
01	00	?
02	01	MIDI Control On
03	00 00	Levels Channel
05	00 01	Scene Recall Channel
07	00 02	FXA Recall Channel
09	00 03	FXB Recall Channel
11	00 00	Main Level Control Channel
13	00 00	FXA Level Control Channel
15	00 00	FXB Level Control Channel
17	00 00	FXA Mute Control Channel
19	00 00	FXB Mute Control Channel
25	01	? (only present on read, not write)

60 System Read

Some stuff from the "System Settings" page and some other stuff from the buttons/knobs on the right.

Response:

Offset	Example	Description
00	60	Command (but 0x6C)
...
25	0D 0C	Monitor Level
27	08 00	Phones Level
...
31	00 04	FXA Level
33	00 04	FXB Level
35	00 04	Solo Level
...
41	0C	Bitfield: 04: FXA Pre2/Post 08: FXB Pre2/Post
42		?
43	0F	Bitfield: 01: Aux1 Pre2/Post 02: Aux2 Pre2/Post 04: Aux3 Pre2/Post 08: Aux4 Pre2/Post
44	03	Bitfield: 01: Talkback Aux1-2 02: Talkback Aux3-4
45	01	Bitfield: 01: Solo PFL (0: AFL) 08: TALK
46	04	Bitfield: 02: Monitor Main 04: Monitor Solo 08: Monitor Digital
...
49	03 0C	03 0C: FXB Aux1-4
51	0F	0F: FXA Aux1-4
52	00	Recalling Bitfield: 01: Mute 02: FX 04: GEQ 08: Pots
53	00	Recalling Bitfield: 01: Assigns 02: EQ&Dyn 04: Aux Mix 08: Faders
...
57	00	? (only present on read, not write)

6A xx Channel State Write

On writes, no "chunking" is applied, it's simply the same data as in the Channel State Read command (see below).

6B xx Channel State Read

Reads the state of channel xx (see Channels below for the mapping).
The software only requests this after detecting a "Channel State Changed" in the "General Status Request".
It also follows the "chunking" mentioned above.

All two-byte values below are split-nibble encoded.

Response:

Offset	Example	Description
00	6B	Command
01	00	Channel
02	03 08	Main Level (fader)
04	07 02	Pan
06	0F 0F	Pan (when linked, same value)
08	00 00	Aux1 Level
10	00 00	Aux2 Level
12	00 00	Aux3 Level
14	00 00	Aux4 Level
...
28	00 00	FXA Level
30	00 00	FXB Level
32	08 00	Aux1/2 Pan (when linked)
34	08 00	Aux3/4 Pan (when linked)
...
44	09 0C	HPF Frequency
46	08 03	EQ Low Frequency
48	00 00	?
50	09 04	EQ Mid Frequency
...
62	04 06	EQ Low Gain
64	00 00	?
66	00 00	EQ Mid Gain
68	08 00	?
70	0F 0F	Compressor Threshold
72	08 00	Compressor Ratio
74	08 00	Compressor Response
76	00 00	?
78	00 00	Compressor Gain
...
84	00 00	Gate
...
106	00	Bitfield: 01: HPF On
107	00	Bitfield: 08: Gate On
108	0A	Bitfield: 02: Compressor On 04: Compressor Auto 08: EQ High On
109	00	Bitfield: 02: EQ Low On 08: EQ High On
110	00	Bitfield: 01: EQ Low Shelf On 04: EQ Mid Hi Q 08: EQ High Shelf On
111	05	Bitfield: 01: Phantom Power On 02: USB Audio Input On 04: Polarity 08: Digital Out
112	06	Bitfield: 01: Mute 02: Solo 04: Link
...
121	00	?

6C 01 xx GEQ Write

Graphic equalizer configuration write.
Contains all 31 band gain values just one after another. Mixer responds with 10 (on success?).

Payload:

Offset	Example	Description
00	6C	Command (but 0x6C)
01	01 00	?
03	01	EQ On
04-64	08 00	Band 1-31 Gain (-16.0 to +15.8dB)
65	00	?

GEQ Bands (Hz):

6D 01 xx GEQ Read

Graphic Equalizer Read. Payload formatted exactly like "write" above.

6C 03 xx FX Write

6D 03 xx FX Read

6E Fader Position Read

Reads all fader positions.
The software only requests this after detecting a "Fader Positions Changed" in the "General Status Request".
Fader position is one byte 04-FF, but the nibbles spread across two bytes, big endian.

Response:

Offset	Example	Description
00	6E	Command
01-31	00 04	Fader Position Ch1-Aux4 (see channels)
33	0F 0F	Fader Position Main
35	00 05	FXA Knob
37	00 05	FXB Knob
39	00 00	?
41	06 01	?

6F System Write

See System Read.

Channels

• 00-07: Channels 1 - 8
• 08-0B: Channels 9/10 - 15/16 (stereo channels)
• 0C-0F: Aux 1-4
• 10: Main
• 11-12: FXA/FXB