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Please see Azure Cognitive Services for Speech documentation for the latest supported speech solutions.

Modify Speech Recognition Engine Properties

Introduction

This document describes the properties of speech recognition (SR) engines that comply with the Microsoft Speech Platform. Applications can modify the properties of a speech recognition (SR) engines using the methods of the ISpProperties interface.

ISpProperties

The ISpProperties interface enables the application to get or set various attributes for an instance of ISpRecognizer. The attributes are passed to the engine via the ISpProperties interface. Property values set using the ISpProperties methods remain in effect only for the current instance of ISpRecognizer, after which they revert to their default settings.

ISpProperties are identified by a unique LONG value. The Speech Platform defines certain attributes known as system attributes. The range of these attributes is from 0x0001 to 0xffff. ISpProperties attributes for vendors are defined by a unique high word value (two ANSI characters that identify the engine vendor).

Attributes may be LONGs, strings, or memory addresses.

SR Properties

The following table lists the properties of speech recognition that are set by the application and passed to the SR engine via the Speech Platform. These attributes are not required for compliance with the Speech Platform. However, the ranges accompanied by the attributes are required values and the exact interpretation of the values is left to the SR engine. The different implementation is defined by each property. The ranges and defaults for each property in the Speech Platform are also shown.

dwAttrib Value WCHAR Value Meaning Range
SPPROP_RESOURCE_USAGE ResourceUsage The ResourceUsage specifies the engine CPU consumption. As the resource usage increases, so does the required CPU power. 0 - 100
Default = 50
SPPROP_HIGH_CONFIDENCE_THRESHOLD
SPPROP_NORMAL_CONFIDENCE_THRESHOLD
SPPROP_LOW_CONFIDENCE_THRESHOLD
 HighConfidenceThreshold
NormalConfidenceThreshold
LowConfidenceThreshold		 The threshold values are used to divide a confidence scale into four portions: rejected, low, medium, and high. The location of the low confidence, normal confidence, and high confidence markers control how the confidence of a word is labeled.
  • The HighConfidenceThreshold (HCT) separates the high and medium confidence range.
  • The NormalConfidenceThreshold (NCT) separates the medium and the low confidence thresholds.
  • The LowConfidenceThreshold (LCT) separates the low and rejected confidence range.
If the all three confidences are equal to 0, then all words will have high confidence. If all three confidences are equal to 100, then all words will have low confidence.

Note: SPPROP_LOW_CONFIDENCE_THRESHOLD is not used by the Microsoft Speech Platform.

 0 - 100
Defaults:
LCT = 20
NCT = 50
HCT = 80
SPPROP_REJECTION_CONFIDENCE_THRESHOLD CFGConfidenceRejectionThreshold The speech recognition engine accepts full utterances with confidence scores above or equal to this threshold, and rejects full utterances with phrase confidence scores below this threshold. This property accepts the following values:
  • The value -1 causes the engine to use its default value.
  • A value in the range of 0-100 sets the phrase confidence rejection threshold to the specified value. If this value is set to 0, the speech recognition accepts all utterances. If this value is set to 100, the speech recognition engine rejects all utterances.
This property is not to be confused with SPPROP_HIGH_CONFIDENCE_THRESHOLD, SPPROP_NORMAL_CONFIDENCE_THRESHOLD, or SPPROP_LOW_CONFIDENCE_THRESHOLD, which are used to determine how any given confidence value is categorized (low, medium, or high).		 -1
0-100
SPPROP_RESPONSE_SPEED ResponseSpeed This indicates the amount of silence the engine looks for before completing a recognition. This attribute is used when the recognition is not ambiguous. For example, in the case of a context-free grammar (CFG) which has two sentences: 1) new game please and 2) new game, a non-ambiguous recognition would be "new game please." 0 - 10,000ms
Default = 500ms
SPPROP_COMPLEX_RESPONSE_SPEED ComplexResponseSpeed This indicates the amount of silence that the engine will look for before completing a recognition. This attribute is used when the recognition is ambiguous. For example, in the case of a CFG which has two sentences: 1) new game please and 2) new game, an ambiguous recognition would be "new game." This property's value must be greater than the ResponseSpeed value. ResponseSpeed - 10,000ms
Default = 750ms
SPPROP_ENGINE_THREAD_PRIORITY EngineThreadPriority Sets the priority of the engine thread(s). The range of permitted values is defined by the OS.
  • The minimum value is min(THREAD_PRIORITY_IDLE,THREAD_PRIORITY_HIGHEST)
  • The maximum value is max(THREAD_PRIORITY_IDLE,THREAD_PRIORITY_HIGHEST)
The values of these constants are in defined winbase.h.		 Defined by the OS
SPPROP_ASSUME_CFG_TRUSTED_SOURCE AssumeCFGFromTrustedSource Bypasses file integrity checks when loading a CFG, to reduce load time. This should *only* be used by applications that can guarantee that the CFG they are loading has previously been compiled by the application (or by another application it trusts) and has been stored in a secure location where it could not be edited by a malicious agent. Default = 0 (property is OFF), or
1 (property is ON)