DAX Version 2 - Improvements and Updates

Starting with SmartSDR v4.2.17, the DAX functionality has been completely redesigned and is now called DAXv2. This update delivers significant architectural improvements, enhanced low-latency performance, and improved compatibility and stability with modern Windows systems.

Below is an overview of the key changes and enhancements introduced with DAXv2.

Summary of Improvements

DAXv2 delivers:

• Dramatically reduced audio latency

• Elimination of ISR/DPC-related audio issues

• Improved Windows 11 compatibility

• Resolution of portctl.sys BSoD events

• Simplified DAX driver architecture

• Reduced and dynamically managed DAX audio endpoints (devices)

These enhancements significantly improve reliability and performance when operating digital modes with SmartSDR v4.2.17 and later.

Overview of DAXv2 Enhancements

1. Direct Audio Streaming Architecture

DAXv2 is a WDM/KS (Kernel Streaming) kernel-mode driver that enables efficient real-time streaming of audio data to and from the radio. The DAXv2 driver does not affect the data flow, nor the timing of audio processing. 

This new audio streaming architecture achieves ultra-low latency through shared-memory data transfer and immediate clocking.

This improvement is most noticeable when operating digital modes using applications such as WSJT-X, where the reported “Delta” time is typically reduced from approximately 0.3 seconds to 0.1 seconds for most stations.

2. Elimination of ISR and DPC Latency Dependencies

DAXv1 relied on system interrupts (ISRs) for audio processing, making long-duration Deferred Procedure Call (DPC) latency a common cause of audio dropouts and pops.

With DAXv2:

• ISRs (interrupts) are no longer used for audio processing.

• Long-duration DPC latency is no longer a primary concern.

• Audio dropouts caused by interrupt handling are effectively eliminated.

⚠️ Important: Because audio is now processed using shared memory data transfer, overall CPU utilization becomes more critical. If CPU usage exceeds approximately 80% while operating digital modes, momentary interruptions in the data flow between the radio and the DAX application may occur.

3. Full Windows 11 Compatibility

The new DAXv2 driver is fully compatible with Windows 11.

• Core Isolation does not need to be disabled.

• Memory Integrity does not need to be turned off.

• The driver loads normally under standard Windows 11 security configurations.

This resolves common driver-loading issues experienced with earlier versions of DAX.

4. Resolution of portcls.sys BSoD

Occasional Windows system crashes (BSoD) associated with the portcls.sys driver and DAXv1 interactions with third-party audio drivers have been resolved with DAXv2.

The redesigned driver architecture eliminates the underlying conflicts that previously caused these system crashes.

5. Simplified Driver Architecture

DAXv1 required four (4) separate DAX device drivers—one for each DAX device endpoint type.

DAXv2 now uses a single unified device driver:

• FlexRadio DAX

This simplifies driver management, improves stability, and reduces system complexity.

6. Streamlined Audio Endpoint Management

DAXv1 Behavior

The previous DAXv1 implementation created virtual audio “cables,” requiring two Windows sound device endpoints per cable: a normal and a "reserved" DAX endpoint device for each DAX channel.

• Total audio endpoints: 28

• Half of the endpoints were reserved exclusively for internal DAX use.

• DAX Audio Endpoints were always active even when DAX was not in use.

This resulted in numerous Windows audio devices being permanently visible in the Sound Control Panel.

DAXv2 Behavior

With DAXv2:

• Device audio endpoints are dynamically initialized when the DAX application starts.  They will only be visible in the Windows Device Manager once the DAX application has been started.

• Total audio endpoints reduced from 28 to 14, eliminating the "reserved" DAXv1 audio endpoints.

• The DAX audio endpoints are only active during operation.

• DAXv2 audio endpoints utilize a new naming convention.

This results in:

• Fewer Windows audio devices

• Reduced system overhead

• Cleaner device management

⚠️ Important: Due to the updated DAXv2 audio endpoint naming convention, previously configured digital mode or other audio applications using DAX audio devices will need to be reconfigured to use the new DAXv2 audio endpoint names.

Below is a table mapping DAXv2 device endpoints to DAXv1 device endpoints.  Note that the device names have changed slightly for DAXv2, and the DAX driver name is listed as a suffix in parentheses.

Below is an image of the Windows Device Manager showing the new DAXv2 audio endpoints and the new DAXv2 Windows device driver.