### External Audio Output Devices

## Using a 3rd Party Audio Player

QA40xPlot has the ability to play the test tones to any Windows sound device. This is great if you want to test a DAC or other audio player, or the DUT has an internal DAC. Some DACs will work better than others. The program tries to attach to a device using WASAPI in exclusive mode for best latency. This may require resampling to the device native settings. If that fails then the attachment is shared and goes through a mixer/resampler which adds variable latency. Try to ensure the device you wish to attach is not the default Windows sound output.

Due to startup issues with external players the first acquisition is done twice when an external player is also playing. If you aren't using the player, then for best performance make sure that the Play Audio With is set to QA40x.

There are 4 settings in the settings tab that determine how this works.

Play Audio With : select which devices generate the test tones. Selections include both devices, only the windows sound device, or only the QA40x.

Play Device Channels: define which input channels are being fed by the external player so that appropriate latency correction is applied. Selections include none, left, right, and L+R (left and right). This is only used with the direct USB support, not the REST support.

Play Device Name: this pull-down lists all Windows sound devices. Select one. Being on the Windows device list is not a guarantee that it works with QA40xPlot.

Play Device Delay: specify the latency of the external sound player (the time before received data begins). This can be either a specific time in ms or QA40xPlot can search for the data start up to a maximum specified time. A negative number is treated as specifying the maximum. A typical target is ~ 50ms.

### FFT Windowing

Using Kaiser windowing for 3rd party audio inputs is a good way to 'ignore' the latency variations in the signal. Unlike Hann windowing (the default), Kaiser will minimize much of the low-end noise generated by the latency while still providing very good accuracy.

### Tested

A few USB DACs have been tested that work fine. This includes Atom DAC+, SMSL DO100, and the Motu M4. Tests with bluetooth DACs have been less successful. They function but timing is irregular, latency is very high and variable, and often the generated audio is choppy.

### USB Connection

If your QA40x is plugged into a USB Hub we recommend plugging the test DAC into a different USB port on the PC to avoid contention.