Voice Capture DSP

An object that encapsulates several DSPs related to voice capture.

CLSID

CLSID_CWMAudioAEC

Interfaces

• IMediaObject
• IPropertyStore

Properties

• MFPKEY_WMAAECMA_DEVICE_INDEXES
• MFPKEY_WMAAECMA_DEVICEPAIR_GUID
• MFPKEY_WMAAECMA_DMO_SOURCE_MODE
• MFPKEY_WMAAECMA_FEATR_AES
• MFPKEY_WMAAECMA_FEATR_AGC
• MFPKEY_WMAAECMA_FEATR_CENTER_CLIP
• MFPKEY_WMAAECMA_FEATR_ECHO_LENGTH
• MFPKEY_WMAAECMA_FEATR_FRAME_SIZE
• MFPKEY_WMAAECMA_FEATR_MICARR_BEAM
• MFPKEY_WMAAECMA_FEATR_MICARR_MODE
• MFPKEY_WMAAECMA_FEATR_MICARR_PREPROC
• MFPKEY_WMAAECMA_FEATR_NOISE_FILL
• MFPKEY_WMAAECMA_FEATR_NS
• MFPKEY_WMAAECMA_FEATR_VAD
• MFPKEY_WMAAECMA_FEATURE_MODE
• MFPKEY_WMAAECMA_MIC_GAIN_BOUNDER
• MFPKEY_WMAAECMA_MICARRAY_DESCPTR
• MFPKEY_WMAAECMA_QUALITY_METRICS
• MFPKEY_WMAAECMA_RETRIEVE_TS_STATS
• MFPKEY_WMAAECMA_SYSTEM_MODE

Remarks

Unlike the other DSPs, the voice capture object encapsulates multiple DSPs in a single object, and the object is a DMO object only (it does not implement IMFTransform). The voice capture DMO includes the following DSP components:

• Acoustic echo cancellation (AEC)
• Microphone array processing
• Noise suppression
• Automatic gain control
• Voice activity detection

Applications can turn each component on and off individually.

The voice capture DMO supports two modes of operation, filter mode and source mode. In filter mode, the application sends audio samples from the microphone and from the speaker line to the DMO, and the DMO produces output.

In source mode, the application does not need to deliver samples to the DMO. Instead, the DMO manages all of the operations on the audio devices, including initializing the devices, capturing and synchronizing the audio streams, calculating time stamps, and retrieving the geometry of the microphone array. Using source mode, the application simply configures the DMO, and the output from the DMO is a clean, processed microphone signal. Source mode is significantly easier to use than filter mode, and is recommended for most applications.

Currently the voice capture DMO supports only single-channel acoustic echo cancellation (AEC), so the output from the speaker line must be single-channel. If microphone array processing is disabled, multi-channel input is folded down to one channel for AEC processing. If both microphone array processing and AEC processing are enabled, AEC is performed on each microphone element before microphone array processing.

About Microphone Array Processing

A microphone array is a set of closely positioned microphones. Microphone arrays achieve better directionality than a single microphone, because the acoustic waves arrive at each microphone at a slightly different time. For more information on microphone arrays see the Web articles Microphone Array Support in Windows Vista and How to Build and Use Microphone Arrays for Windows Vista.

Requirements

Client: Requires Windows Vista or Windows XP.

Header: Include wmcodecdsp.h.

Library: Use mfwmaaec.dll.

See Also

• Digital Signal Processors
• Using the Voice Capture DSP