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USB Audio 2.0 drivers

Starting with Windows 10, release 1703, a USB Audio 2.0 driver is shipped with Windows. It's designed to support the USB Audio 2.0 device class. The driver is a WaveRT audio port class miniport.

The driver is named: usbaudio2.sys. The associated information (INF) file is usbaudio2.inf.

The driver identifies in device manager as USB Audio Class 2 Device. This name is overwritten with a USB product string, if it's available.

When a compatible device is attached to the system, the driver is enabled. If a partner driver exists on the system or Windows Update, that driver is installed and overrides the class driver.

Architecture

The usbaudio2.sys driver fits within the wider architecture of Windows USB Audio as shown.

Stack diagram illustrating the Windows USB Audio architecture with ks.sys at the top and USB Audio devices at the bottom.

This article refers to the following USB specifications that define USB Audio.

  • USB-2 refers to the Universal Serial Bus Specification, Revision 2.0
  • ADC-2 refers to the USB Device Class Definition for Audio Devices, Release 2.0
  • FMT-2 refers to the Audio Data Formats specification, Release 2.0

The USB-IF is a special interest group that maintains the Official USB Specification, test specifications, and tools.

Audio formats

The driver supports the formats listed here. An alternate setting, which specifies another format defined in FMT-2, or an unknown format, is ignored.

Type I formats (FMT-2 2.3.1):

  • PCM Format with 8..32 bits per sample (FMT-2 2.3.1.7.1)
  • PCM8 Format (FMT-2 2.3.1.7.2)
  • IEEE_FLOAT Format (FMT-2 2.3.1.7.3)

Type III formats (FMT-2 2.3.3 and A.2.3):

  • IEC61937_AC-3
  • IEC61937_MPEG-2_AAC_ADTS
  • IEC61937_DTS-I
  • IEC61937_DTS-II
  • IEC61937_DTS-III
  • TYPE_III_WMA

Feature descriptions

This section describes the features of the USB Audio 2.0 driver.

Audio function topology

The driver supports all entity types defined in ADC-2 3.13.

Each Terminal Entity must have a valid clock connection in compatible USB Audio 2.0 hardware. The clock path optionally includes Clock Multiplier and Clock Selector units and must end in a Clock Source Entity.

The driver supports one single clock source only. If a device implements multiple clock source entities and a clock selector, the driver uses the clock source that is selected by default. It doesn't modify the clock selector's position.

A Processing Unit (ADC-2 3.13.9) with more than one input pin isn't supported.

An Extension Unit (ADC-2 3.13.10) with more than one input pin isn't supported.

Cyclic paths in the topology aren't allowed.

Audio streaming

The driver supports the following endpoint synchronization types (USB-2 5.12.4.1):

  • Asynchronous IN and OUT
  • Synchronous IN and OUT
  • Adaptive IN and OUT

For the asynchronous OUT case, the driver supports explicit feedback only. A feedback endpoint must be implemented in the respective alternate setting of the AS interface. The driver doesn't support implicit feedback.

There's currently limited support for devices using a shared clock for multiple endpoints.

For the Adaptive IN case, the driver doesn't support a feed forward endpoint. If such an endpoint is present in the alternate setting, the driver ignores it. The driver handles the Adaptive IN stream in the same way as an Asynchronous IN stream.

The size of isochronous packets created by the device must be within the limits specified in FMT-2.0 section 2.3.1.1. This requirement means that the deviation of actual packet size from nominal size must not exceed +/- one audio slot. Audio slot = channel count samples.

Descriptors

An audio function must implement exactly one AudioControl Interface Descriptor (ADC-2 4.7) and one or more AudioStreaming Interface Descriptors (ADC-2 4.9). A function with an audio control interface but no streaming interface isn't supported.

The driver supports all descriptor types defined in ADC-2, section 4. The following sections provide comments on some descriptor types.

Class-Specific AS interface descriptor

For details on this specification, see ADC-2 4.9.2.

An AS interface descriptor must start with alternate setting zero with no endpoint (no bandwidth consumption). Further alternate settings must be specified in ascending order in compatible USB Audio 2.0 hardware.

An alternate setting with a format that the driver doesn't support is ignored.

Each nonzero alternate setting must specify an isochronous data endpoint, and optionally a feedback endpoint. A nonzero alternate setting without any endpoint isn't supported.

The bTerminalLink field must see a Terminal Entity in the topology. Its value must be identical in all alternate settings of an AS interface.

The bFormatType field in the AS interface descriptor must be identical to bFormatType specified in the Format Type Descriptor (FMT-2 2.3.1.6).

For Type I formats, exactly one bit must be set to one in the bmFormats field of the AS interface descriptor. Otherwise, the driver ignores the format.

To save bus bandwidth, one AS interface can implement multiple alternate settings with the same format (in terms of bNrChannels and AS Format Type Descriptor) but different wMaxPacketSize values in the isochronous data endpoint descriptor. For a sample rate, the driver selects the alternate setting with the smallest wMaxPacketSize that can fulfill the data rate requirements.

Type I format type descriptor

For details on this specification, see FMT-2 2.3.1.6.

The following restrictions apply:

Format Subslot size Bit resolution
Type I PCM format: 1 <= bSubslotSize <= 4 8 <= bBitResolution <= 32
Type I PCM8 format: bSubslotSize == 1 bBitResolution == 8
Type I IEEE_FLOAT format: bSubslotSize == 4 bBitResolution == 32
Type III IEC61937 formats: bSubslotSize == 2 bBitResolution == 16

Class-specific AS isochronous audio data endpoint descriptor

For details on this specification, see ADC-2 4.10.1.2.

The MaxPacketsOnly flag in the bmAttributes field isn't supported and is ignored.

The fields bmControls, bLockDelayUnits, and wLockDelay are ignored.

Class requests and interrupt data messages

The driver supports a subset of the control requests defined in ADC-2, section 5.2. It supports interrupt data messages (ADC-2 6.1) for some controls. The following table shows the subset that is implemented in the driver.

Entity Control GET CUR SET CUR GET RANGE INTERRUPT
Clock Source Sampling Frequency Control x x x
Clock Selector Clock Selector Control x
Clock Multiplier Numerator Control x
Denominator Control x
Terminal Connector Control x x
Mixer Unit Mixer Control x x x
Selector Unit Selector Control x x
Feature Unit Mute Control x x x
Volume Control x x x x
Automatic Gain Control x x
Effect Unit –
Processing Unit –
Extension Unit –

Additional information on the controls and requests is available in the following sections.

Clock source entity

For details on this specification, see ADC-2 5.2.5.1.

At a minimum, a Clock Source Entity must implement Sampling Frequency Control GET RANGE and GET CUR requests (ADC-2 5.2.5.1.1) in compatible USB Audio 2.0 hardware.

The Sampling Frequency Control GET RANGE request returns a list of subranges (ADC-2 5.2.1). Each subrange describes a discrete frequency, or a frequency range. A discrete sampling frequency must be expressed by setting MIN and MAX fields to the respective frequency and RES to zero. Individual subranges must not overlap. If a subrange overlaps a previous one, the driver ignores it.

A Clock Source Entity that implements one single fixed frequency only doesn't need to implement Sampling Frequency Control SET CUR. It implements GET CUR, which returns the fixed frequency. It also implements GET RANGE, which reports one single discrete frequency.

Clock selector entity

For details on this specification, see ADC-2 5.2.5.2.

The USB Audio 2.0 driver doesn't support clock selection. The driver uses the Clock Source Entity, which is selected by default and never issues a Clock Selector Control SET CUR request. The Clock Selector Control GET CUR request (ADC-2 5.2.5.2.1) must be implemented in compatible USB Audio 2.0 hardware.

Feature unit

For details on this specification, see ADC-2 5.2.5.7.

The driver supports one single volume range only. If the Volume Control GET RANGE request returns more than one range, the driver ignores subsequent ranges.

The volume interval expressed by the MIN and MAX fields should be an integer multiple of the step size specified in the RES field.

If a feature unit implements single channel controls and a primary control for Mute or Volume, then the driver uses the single channel controls and ignores the primary control.

Additional information for hardware manufacturers

Hardware manufacturers should test their existing and new devices against the supplied in-box driver.

There isn't any specific partner customization that is associated with the in-box USB Audio 2.0 driver.

This INF file entry, which is provided in an update to Windows Release 1703, is used to identify that the in-box driver is a generic device driver.

GenericDriverInstalled,,,,1

The in-box driver registers for the following compatible IDs with usbaudio2.inf.

USB\Class_01&SubClass_00&Prot_20
USB\Class_01&SubClass_01&Prot_20
USB\Class_01&SubClass_02&Prot_20
USB\Class_01&SubClass_03&Prot_20

See the USB Audio 2.0 specification for subclass types.

USB Audio 2.0 Devices with MIDI (subclass 0x03 above) enumerate the MIDI function as a separate multiple function device with usbaudio.sys (USB Audio 1.0 driver) loaded.

The USB Audio 1.0 class driver registers this compatible ID with wdma_usb.inf.

USB\Class_01

And has these exclusions:

USB\Class_01&SubClass_00&Prot_20
USB\Class_01&SubClass_01&Prot_20
USB\Class_01&SubClass_02&Prot_20
USB\Class_01&SubClass_03&Prot_20

Due to a limitation of the Windows audio stack, an arbitrary number of channels, greater than eight, aren't supported in shared mode.

IHV USB Audio 2.0 drivers and updates

For IHV provided driver USB Audio 2.0 drivers, those drivers continue to be preferred for their devices over the Microsoft in-box driver unless they update their driver to explicitly override this behavior and use the in-box driver.

Audio jack registry descriptions

Starting in Windows 10 release 1703, IHVs that create USB Audio Class 2.0 devices having one or more jacks have the capability to describe these jacks to the in-box Audio Class 2.0 driver. The in-box driver uses the supplied jack information when handling the KSPROPERTY_JACK_DESCRIPTION for this device.

Jack information is stored in the registry in the device instance key (HW key).

The following list describes the audio jack information settings in the registry:

REG_DWORD  T<tid>_NrJacks                 # of the jack on this device
REG_DWORD  T<tid>_J<n>_ChannelMapping     Channel mask. The value is defined in ksmedia.h. e.g. SPEAKER_FRONT_RIGHT or KSAUDIO_SPEAKER_5POINT1_SURROUND
REG_DWORD  T<tid>_J<n>_ConnectorType      The enum value is define in EPcxConnectionType.
REG_DWORD  T<tid>_J<n>_GeoLocation        The enum value is define in EPcxGeoLocation.
REG_DWORD  T<tid>_J<n>_GenLocation        The enum value is define in EPcxGenLocation.
REG_DWORD  T<tid>_J<n>_PortConnection     The enum value is define in EPxcPortConnection.
REG_DWORD  T<tid>_J<n>_Color              The color needs to be represent by RGB like this: 0x00RRGGBB (NOT a COLORREF).
  • <tid> = terminal ID, as defined in the descriptor
  • <n> = Jack number (1 ~ n)

Convention for <tid> and <n> is:

  • Base 10 (8, 9, 10 rather than 8, 9, a)
  • No leading zeros
  • n is 1-based (first jack is jack 1 rather than jack 0)

For example: T1_NrJacks, T1_J2_ChannelMapping, T1_J2_ConnectorType

For more audio jack information, see KSJACK_DESCRIPTION structure.

These registry values can be set in various ways:

  • By using custom INFs, which wrap the in-box INF for the purpose to set these values.
  • Directly by the hardware device by using a Microsoft OS Descriptor for USB devices, as in the example in the next section. For more information, see Microsoft OS Descriptors for USB Devices.

Microsoft OS descriptors for USB Example

The following Microsoft OS descriptors for USB example contains the channel mapping and color for one jack. The example is for a noncomposite device with single feature descriptor.

The IHV vendor should extend it to contain any other information for the jack description.

UCHAR Example2_MSOS20DescriptorSetForUAC2 [0x76] = {
    //
    // Microsoft OS 2.0 Descriptor Set Header
    //
    0x0A, 0x00,             // wLength - 10 bytes
    0x00, 0x00,             // MSOS20_SET_HEADER_DESCRIPTOR
    0x00, 0x00, 0x0?, 0x06, // dwWindowsVersion – 0x060?0000 for future Windows version
    0x76, 0x00,             // wTotalLength – 118 bytes // update later

    //
    // Microsoft OS 2.0 Registry Value Feature Descriptor
    //
    0x42, 0x00,             // bLength - 66 bytes
    0x04, 0x00,             // wDescriptorType – 5 for Registry Property
    0x04, 0x00,             // wPropertyDataType - 4 for REG_DWORD
    0x34, 0x00,             // wPropertyNameLength – 52 bytes
    0x54, 0x00, 0x30, 0x00, // Property Name - "T01_J01_ChannelMapping"
    0x31, 0x00, 0x5f, 0x00,
    0x4a, 0x00, 0x30, 0x00,
    0x31, 0x00, 0x5f, 0x00,
    0x43, 0x00, 0x68, 0x00,
    0x61, 0x00, 0x6e, 0x00,
    0x6e, 0x00, 0x65, 0x00,
    0x6c, 0x00, 0x4d, 0x00,
    0x61, 0x00, 0x70, 0x00,
    0x70, 0x00, 0x69, 0x00,
    0x6e, 0x00, 0x67, 0x00,
    0x00, 0x00
    0x04, 0x00,                       // wPropertyDataLength – 4 bytes
    0x02, 0x00, 0x00, 0x00  // PropertyData - SPEAKER_FRONT_RIGHT

    //
    // Microsoft OS 2.0 Registry Value Feature Descriptor
    //
    0x2A, 0x00,             // bLength - 42 bytes
    0x04, 0x00,             // wDescriptorType – 5 for Registry Property
    0x04, 0x00,             // wPropertyDataType - 4 for REG_DWORD
    0x1C, 0x00,             // wPropertyNameLength – 28 bytes
    0x54, 0x00, 0x30, 0x00, // Property Name - "T01_J01_Color"
    0x31, 0x00, 0x5f, 0x00,
    0x4a, 0x00, 0x30, 0x00,
    0x31, 0x00, 0x5f, 0x00,
    0x43, 0x00, 0x6f, 0x00,
    0x6c, 0x00, 0x6f, 0x00,
    0x72, 0x00, 0x00, 0x00,
    0x04, 0x00,             // wPropertyDataLength – 4 bytes
    0x00, 0x00, 0xff, 0x00  // PropertyData - 0xff0000 - RED }

Troubleshooting

If the driver doesn't start, check the system event log. The driver logs events can indicate the reason for the failure. You can manually collect log as described in Collecting audio logs the old-fashioned way. If the failure might indicate a driver problem, report it using the Feedback Hub described here, and include the logs.

For information on how to read logs for the USB Audio 2.0 class driver using supplemental TMF files, see Report problems, with logs, and suggest features, with the Feedback Hub. For general information on working with TMF files, see Displaying a Trace Log with a TMF File.

For information on Audio services not responding and USB Audio device doesn't work in Windows 10 version 1703, see USB Audio Not Playing.

Feedback Hub

If you run into a problem with this driver, collect audio logs and then follow steps outlined in Report problems, with logs, and suggest features, with the Feedback Hub.

Driver development

Thesycon developed this USB Audio 2.0 class driver. Microsoft supports it.

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