# VoiceActivityDetection Node¶

## Outline of the node¶

This node delimits the a speech-present period.

## Typical connection¶

This node is connected with the VoiceActivityDetection node. Typical connection of this node is depicted as follows:

## Input-output and property of the node¶

### Input¶

**AUDIO_SPECTRUM**Matrixd<complex<float> >- Windowed spectrum data. A row index is channel, and a column index is frequency.

### Output¶

**VAD_DECISION**Vector<ObjectRef>- Decision of speech-present frame

### Parameters¶

Parameters of this node are listed as follows:

Parameter name | Type | Default value | Unit | Description |
---|---|---|---|---|

VAD_NOISE_DURATION | float | 3.0 | second | Time duration to be regarded as “noise” from the first frame |

VAD_THRESHOLD | float | 50.0 | Threshold for voice activity decision. | |

ADVANCE | int | 160 | sample | The length in sample between a frame and a previous frame. |

SAMPLING_RATE | int | 16000 | Hz | Sampling rate. |

## Detail of the node¶

This node estimates the voice activity by using log likelifood ratio of speech and noise variances of the zero-mean Gaussian statistical model [1]. Let \(X_{l/r}\left[f, n\right]\) be an input audio signal at frequency bin \(f\) and time frame \(n\), this method regards speech-present when following equation is satisfied:

\(\frac{1}{F} \sum^{F}_{f=1} \gamma \left[f,n\right]- {\rm log} \gamma \left[f,n\right] -1 > \eta_{VAD}\),

\(\lambda_N \left[f\right] = E\left|N_l\left[f\right] \cdot N_r\left[f\right]^{\ast}\right|\),

\(\gamma\left[f,n\right]=\left|X_l \left[f,n\right] \cdot X_r\left[f,n\right]^{\ast}\right|/ \lambda_N\left[f\right]\),

where \(N\left[f\right]\) and \(\eta_{VAD}\) represent the variance of a estimated noise and threshold parameter, respectively.