Vendor-Specific Recognizer Properties

The following parameters are LumenVox-specific extensions to the MRCP specification. They can be controlled via the media_server.conf file, located in the config directory of the Windows LumenVox installation folder. By default, this location is C:\Program Files\Lumenvox\config\.

In Linux, edit the media_server.conf file in /etc/lumenvox/.

They may also be set with the appropriate header as part of a RECOGNITION or SET-PARAMS method; see Specifying Vendor-Specific Properties via MRCP Headers below.

See Configuration Parameters for more information about changing various MRCP parameters.

wind-back-time

The length of audio wound back at the beginning of voice.

It helps in the situation of weak speech onset. The resolution of this parameter is 40 ms and it is rounded to the closes multiple of 40ms, which means setting this value to 139 ms is the same as setting it to 120 and setting this value to 141 ms is the same as setting it to 160 ms. It is specified in milliseconds.

Range: >0

See STREAM_PARM_VAD_WIND_BACK in the LumenVox API documentation for more details.

Default: 480

vad-stream-init-delay

The length of audio (in milliseconds) that the VAD module uses to estimate the acoustic environment.

Accurate VAD depends on good estimation of acoustic environment. The VAD module uses the first a couple of frames of audio to estimate the acoustic environment, such as noise level. The length of this period is defined by this parameter.

Range: >0

See STREAM_PARM_VAD_STREAM_INIT_DELAY in the LumenVox API documentation for more details.

Default: 100

vad-bargein-threshold

VAD speech sensitivity setting.

A higher value makes the VAD more sensitive to speech which means that the VAD is very sure the data is speech before barge in. Raising the value will reject more false positives/noises However, it may mean that some speech that is on the borderline may be rejected This value should not be changed from the default without significant tuning and verification.

Range: 0 - 100 (MRCP v1 and MRCP v2)

See STREAM_PARM_VAD_BARGEIN_THRESHOLD in the LumenVox API documentation for more details.

Default: 50

compatibility_mode

Enables compatibility encoding of results

This option may need to be enabled to match the output of LumenVox decodes with those of other vendors.

Please contact LumenVox support for more specific details

Default: 0

Specifying Vendor-Specific Properties via MRCP Headers

As mentioned previously, you may specify the above parameters in an MRCP header. You must use the following format. Note that a semicolon (";") is used as the delimiter:

Vendor-Specific: com.lumenvox.wind-back-time=300;com.lumenvox.vad-stream-init-delay=200

This header field may be specified in RECOGNIZE or SET-PARAMS method during an MRCP session. The following header field names may be used: