VU Indicators

[TheOnlyJoey]

I have a hunch where the VU values are coming from in the usb spec, but need a dedicated session to finalize and rig a simple VU meter, probably based on a ImGui::VSliderFloat

[schlupmann]

If you haven't already done this, following data (gathered from my iD14) could help you with the VU meter :

The Meter Data is retrieved via active Polling of the DSP memory. The host must continuously query the device to update the UI meters (I have set a rate at 30Hz and that works perfectly with the iD14).

Target: Mixer Matrix Unit (0x3C)
Command: GET_MEM (Class Interface Request)

Parameter	Value	Description
bmRequestType	0xA1	Device-to-Host | Class | Interface
bRequest	0x03	GET_MEM (Get Memory)
wValue	0x0000	Address Offset
wIndex	0x3c04	Target Unit ID
wLength	0x0020	Request exactly 32 Bytes

C++ Implementation (using libusb):

// Buffer to hold 16 channels * 2 bytes = 32 bytes
unsigned char meter_data[32];

// This call should be placed in a separate thread (polling loop)
int result = libusb_control_transfer(
    handle,
    0xA1,           // bmRequestType
    0x03,           // bRequest (GET_MEM)
    0x0000,         // wValue (Offset)
    0x3c04,         // wIndex (Mixer Unit 0x3C via Interface 4)
    meter_data,     // Buffer
    32,             // wLength
    20              // Timeout (ms)
);

Data Format & Channel Mapping

The response is a 32-byte array containing 16 channels of audio level data (that's for iD14)

• Data Type: 16-bit Unsigned Integer (Little Endian).
• Values: 0x0000 (Silence) to 0xFFFF (0dBFS / Clip).
• Packet Order: Analog Inputs -> ID Digital Inputs -> USB Returns.

Byte Offset	Channel Name	Type	Notes
00 - 01	Mic 1	Analog In	Pre-Fader / PFL
02 - 03	Mic 2	Analog In	Pre-Fader / PFL
04 - 05	Digi 1	Optical In
06 - 07	Digi 2	Optical In
08 - 09	Digi 3	Optical In
10 - 11	Digi 4	Optical In
12 - 13	Digi 5	Optical In
14 - 15	Digi 6	Optical In
16 - 17	Digi 7	Optical In
18 - 19	Digi 8	Optical In
20 - 21	DAW 1 (Main L)	USB Return	Software Playback
22 - 23	DAW 2 (Main R)	USB Return	Software Playback
24 - 25	DAW 3 (Cue A L)	USB Return
26 - 27	DAW 4 (Cue A R)	USB Return
28 - 29	DAW 5 (Cue B L)	USB Return
30 - 31	DAW 6 (Cue B R)	USB Return

I hope this is of some help.

[TheOnlyJoey]

Thanks for the report!

I actually found another way to grab the VU information, but this seems to be a bit cleaner.
I was doing a couple of patches at the same time but will migrate some work to develop and see if i can get a good generic implementation going.