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java.lang.Objectedu.cmu.sphinx.frontend.BaseDataProcessor
edu.cmu.sphinx.frontend.feature.DeltasFeatureExtractor
Computes the delta and double delta of input cepstrum (or plp or ...). The
delta is the first order derivative and the double delta (a.k.a. delta
delta) is the second order derivative of the original cepstrum. They help
model the speech signal dynamics. The output data is a FloatData
object with a float array of size three times the original cepstrum, formed
by the concatenation of cepstra, delta cepstra, and double delta cepstra.
The output is the feature vector used by the decoder. Figure 1 shows the
arrangement of the output feature data array:
Figure 1: Layout of the returned features.
Suppose that the original cepstrum has a length of N, the first N elements of the feature are just the original cepstrum, the second N elements are the delta of the cepstrum, and the last N elements are the double delta of the cepstrum.
Figure 2 below shows pictorially the computation of the delta and double
delta of a cepstrum vector, using the last 3 cepstra and the next 3 cepstra.
Figure 2: Delta and double delta vector computation.
Refering to Figure 2, the delta is computed by subtracting the cepstrum that is two frames behind of the current cepstrum from the cepstrum that is two frames ahead of the current cepstrum. The computation of the double delta is similar. It is computed by subtracting the delta cepstrum one time frame behind from the delta cepstrum one time frame ahead. Replacing delta cepstra with cepstra, this works out to a formula involving the cepstra that are one and three behind and after the current cepstrum.
Field Summary | |
static java.lang.String |
PROP_FEATURE_WINDOW
The name of the SphinxProperty for the window of the DeltasFeatureExtractor. |
static int |
PROP_FEATURE_WINDOW_DEFAULT
The default value of PROP_FEATURE_WINDOW. |
Constructor Summary | |
DeltasFeatureExtractor()
|
Method Summary | |
Data |
getData()
Returns the next Data object produced by this DeltasFeatureExtractor. |
void |
initialize()
Initializes this DataProcessor. |
void |
newProperties(PropertySheet ps)
This method is called when this configurable component has new data. |
void |
register(java.lang.String name,
Registry registry)
Register my properties. |
Methods inherited from class edu.cmu.sphinx.frontend.BaseDataProcessor |
getName, getPredecessor, getTimer, setPredecessor, toString |
Methods inherited from class java.lang.Object |
equals, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Field Detail |
public static final java.lang.String PROP_FEATURE_WINDOW
public static final int PROP_FEATURE_WINDOW_DEFAULT
Constructor Detail |
public DeltasFeatureExtractor()
Method Detail |
public void register(java.lang.String name, Registry registry) throws PropertyException
Configurable
register
in interface Configurable
register
in class BaseDataProcessor
PropertyException
public void newProperties(PropertySheet ps) throws PropertyException
Configurable
newProperties
in interface Configurable
newProperties
in class BaseDataProcessor
PropertyException
public void initialize()
BaseDataProcessor
initialize
in interface DataProcessor
initialize
in class BaseDataProcessor
public Data getData() throws DataProcessingException
getData
in interface DataProcessor
getData
in class BaseDataProcessor
DataProcessingException
- if there is a data processing error
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