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USB Audio

About USB Audio

The miniDSP Flex HTx accepts multichannel (8-channel) PCM audio over USB at sample rates up to 96 kHz. The same USB connector is used for playing USB Audio as well as for configuration and Dirac Live calibration.

To play USB Audio from a computer, use the supplied cable to connect the USB 2.0 (Type B) port of the Flex HTx to a free USB port on your computer.

Alternatively, connect a network streamer to the USB port. For examples using the Raspberry Pi, see these application notes on our website:

Note

While some miniDSP processors provide the processed outputs to the computer over USB, the Flex HTx does not.

USB Audio channel mapping

The channel mapping of USB Audio differs from HDMI. They are shown in the table below:

Channel HDMI Audio USB Audio
1 Left Front Left Front
2 Right Front. Right Front
3 LFE Center
4 Center LFE
5 Left Surround Left Back
6 Right Surround Right Back
7 Left Back Left Surround
8 Right Back Right Surround

In the Flex HTx, we have chosen to use the HDMI channel mapping as the default. Some additional configuration may be required for USB Audio:

macOS

The miniDSP Flex HTx is USB Audio compliant, so no drivers need to be installed to play audio on macOS. Open Audio MIDI Setup (in Applications->Utilities) and click on its name in the list on the left-hand side.

miniDSP Flex HTx in macOS Audio MIDI Setup

Set sample rate

Click on the selector next to Format to bring up the sample rate and bit depth selector. Sample rates up to 96 kHz can be selected:

miniDSP Flex HTx in macOS Audio MIDI Setup

Default audio device

To set the Flex HTx as the default audio output device, right-click and select "Use this device for sound output":

Set miniDSP Flex HTx as default macOS output device

Note that individual audio playback apps may allow the Flex HTx to be selected for audio output independently of the system default. They may also control sample rate automatically.

macOS channel mapping

To change the channel mapping to match HDMI, click on the Configure Speakers... button. On the dialog that pops up:

  1. Select "7.1 Rear Surround" from the drop-down selector near the top.
  2. Swap the channel assignment for Center and Subwoofer.

This is highlighted in the screenshot below.

Configure USB channel mapping for Flex HTx in macOS

Windows 11

Note: to play USB audio from Windows, the miniDSP UAC2 driver package must be installed first.

Default audio device

To set the miniDSP Flex HTx as the default audio output device, open the Settings app and navigate to the System → Sound page. Select the Flex HTx with the radio button:

Set miniDSP Flex HTx as default Windows 11 output device

Set sample rate

To change the bit depth and sample rate, click on the rightward angle symbol >. Click the selector next to Format to pop up the sample rate menu. Sample rates up to 96 kHz can be selected:

Set miniDSP Flex HTx sample rate in Windows 11

ASIO

If your audio application supports ASIO® audio drivers, we recommend selecting the miniDSP ASIO Driver in its settings. This typically allows the application to automatically change sample rate. For example, in JRiver Media Center:

Select miniDSP ASIO driver

miniDSP UAC2 control panel

The current settings of the miniDSP Flex HTx can be viewed by opening the miniDSP UAC2 Control Panel from the Windows Start menu (under the miniDSP Ltd folder). This control panel allows you to view current settings. In addition, it can be used to set buffer size, although we recommend that you leave this setting at the default. If you are having an issue with inadequate output volume over USB playback, check the Volume tab.

miniDSP UAC2 control panel

To see the installed version of the UAC2 driver, use the About tab:

miniDSP UAC2 control panel version

Configuration for USB Audio

The difference in channel mapping for USB Audio and HDMI can be confusing. However, it is not too difficult to adapt by using some changes in labeling and channel routing. There are two steps:

  1. Change the input channel labels on the Input Channels tab, as shown in this screenshot:

    Channel naming for USB Audio

  2. Change the routing on the Channel routing tab as shown in this screenshot:

    Channel routing for USB Audio

With this done, the output channel labelling and Mixer tab examples in the rest of this manual are correct.

Tip

If you use both the HDMI and USB inputs for multichannel audio, create a separate preset for each. When switching inputs, switch presets as well.