Why can I not access all channels of my MOTU 24ai audio device when using the Data Acquisition Toolbox?

I am trying to read data from my MOTU 24ai audio DAQ using the session-based interface in the Data Acquisition Toolbox. "daq.getDevices" shows that my device is recognized:

 

>> daq.getDevices 

index Vendor Device ID Description 
----- ----------- --------- ------------------------------------------------------------------ 
4 directsound Audio2 DirectSound Ligne (MOTU AVB USB Audio)

Also, I am able to successfully add audio input channels for all 24 channels, as indicated about the output of session variable:

 

Data acquisition session using DirectSound hardware: 
Will run continuously at 44100 scans/second until stopped. 
Number of channels: 24 
index Type Device Channel MeasurementType Range Name 
----- ---- ------ ------- --------------- ------------- ------------- 
1 audi Audio2 1 Audio -1.0 to +1.0 My Channel 1 
2 audi Audio2 2 Audio -1.0 to +1.0 My Channel 2 
3 audi Audio2 3 Audio -1.0 to +1.0 My Channel 3 
4 audi Audio2 4 Audio -1.0 to +1.0 My Channel 4 
5 audi Audio2 5 Audio -1.0 to +1.0 My Channel 5 
6 audi Audio2 6 Audio -1.0 to +1.0 My Channel 6 
7 audi Audio2 7 Audio -1.0 to +1.0 My Channel 7 
8 audi Audio2 8 Audio -1.0 to +1.0 My Channel 8 
9 audi Audio2 9 Audio -1.0 to +1.0 My Channel 9 
10 audi Audio2 10 Audio -1.0 to +1.0 My Channel 10 
11 audi Audio2 11 Audio -1.0 to +1.0 My Channel 11 
12 audi Audio2 12 Audio -1.0 to +1.0 My Channel 12 
13 audi Audio2 13 Audio -1.0 to +1.0 My Channel 13 
14 audi Audio2 14 Audio -1.0 to +1.0 My Channel 14 
15 audi Audio2 15 Audio -1.0 to +1.0 My Channel 15 
16 audi Audio2 16 Audio -1.0 to +1.0 My Channel 16 
17 audi Audio2 17 Audio -1.0 to +1.0 My Channel 17 
18 audi Audio2 18 Audio -1.0 to +1.0 My Channel 18 
19 audi Audio2 19 Audio -1.0 to +1.0 My Channel 19 
20 audi Audio2 20 Audio -1.0 to +1.0 My Channel 20 
21 audi Audio2 21 Audio -1.0 to +1.0 My Channel 21 
22 audi Audio2 22 Audio -1.0 to +1.0 My Channel 22 
23 audi Audio2 23 Audio -1.0 to +1.0 My Channel 23 
24 audi Audio2 24 Audio -1.0 to +1.0 My Channel 24

However, I can only access the first 2 channels. When I try to read from channels 3 through 24, the reading is just 0. How can I read all 24 channels?

Answer 1

[MathWorks Support Team]

The Data Acquisition Toolbox Session interface uses DirectSound drivers to communicate with audio devices. The behavior you are experiencing might be due to an issue with the manufacturer-provided DirectSound drivers. The manufacturer (MOTU) recommends using ASIO drivers to take advantage of all the MOTU 24ai input and output channels.

MOTU also provides ASIO drivers for interfacing with the MOTU 24ai device. However, the Data Acquisition Toolbox Session interface does not support ASIO drivers. A possible alternative would be to use DSP System Toolbox or Audio System Toolbox, which provide support for devices with ASIO drivers.