edu.cmu.sphinx.frontend.window

Class RaisedCosineWindower

java.lang.Object

edu.cmu.sphinx.util.props.ConfigurableAdapter

edu.cmu.sphinx.frontend.BaseDataProcessor

edu.cmu.sphinx.frontend.window.RaisedCosineWindower

All Implemented Interfaces:

DataProcessor, Configurable

public class RaisedCosineWindower
extends BaseDataProcessor

Slices up a Data object into a number of overlapping windows (usually referred to as "frames" in the speech world). In order to minimize the signal discontinuities at the boundaries of each frame, we multiply each frame with a raised cosine windowing function. Moreover, the system uses overlapping windows to capture information that may occur at the window boundaries. These events would not be well represented if the windows were juxtaposed.

The number of resulting windows depends on the window size and the window shift (commonly known as frame shift in speech world). Figure 1 shows the relationship between the original data stream, the window size, the window shift, and the windows returned.

Figure 1: Relationship between original data, window size, window shift, and the windows returned.

The raised cosine windowing function will be applied to each such window. Since the getData() method returns a window, and multiple windows are created for each Data object, this is a 1-to-many processor. Also note that the returned windows should have the same number of data points as the windowing function.

The applied windowing function, W(n), of length N (the window size), is given by the following formula:

 W(n) = (1-a) - (a * cos((2 * Math.PI * n)/(N - 1)))
 

where a is commonly known as the "alpha" value. This variable can be set by the user using the property defined by PROP_ALPHA. Please follow the links to the see the constant field values. Some values of alpha receive special names, since they are used so often. A value of 0.46 for the alpha results in a window named Hamming window. A value of 0.5 results in the Hanning window. And a value of 0 results in the Rectangular window. The default for this system is the Hamming window, with alpha 0.46 !). Figure 2 below shows the Hamming window function (a = 0.46), using our default window size of 25.625 ms and assuming a sample rate of 16kHz, thus yielding 410 samples per window.

Figure 2: The Hamming window function.

See Also:

Data

Field Summary

Fields

Modifier and Type	Field and Description
static java.lang.String	PROP_ALPHA The property for the alpha value of the Window, which is the value for the RaisedCosineWindow.
static java.lang.String	PROP_WINDOW_SHIFT_MS The property for window shift in milliseconds, which has a default value of 10F.
static java.lang.String	PROP_WINDOW_SIZE_MS The property for window size in milliseconds.
static java.lang.String	WINDOW_SHIFT_SAMPLES
static java.lang.String	WINDOW_SIZE_SAMPLES

Fields inherited from class edu.cmu.sphinx.util.props.ConfigurableAdapter

logger

Constructor Summary

Constructors

Constructor and Description
RaisedCosineWindower()
RaisedCosineWindower(double alpha, float windowSizeInMs, float windowShiftInMs)

Method Summary

Modifier and Type	Method and Description
Data	getData() Returns the next Data object, which is usually a window of the input Data, with the windowing function applied to it.
int	getSampleRate()
float	getWindowShiftInMs() Returns the shift size used to window the incoming speech signal.
void	initialize() Initializes this DataProcessor.
void	newProperties(PropertySheet ps) This method is called when this configurable component needs to be reconfigured.
long	roundToFrames(long samples) Rounds a given sample-number to the number of samples will be processed by this instance including the padding samples at the end..

Methods inherited from class edu.cmu.sphinx.frontend.BaseDataProcessor

getPredecessor, setPredecessor

Methods inherited from class edu.cmu.sphinx.util.props.ConfigurableAdapter

getName, initLogger, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

PROP_WINDOW_SIZE_MS

@S4Double(defaultValue=25.625)
public static final java.lang.String PROP_WINDOW_SIZE_MS

The property for window size in milliseconds.

See Also:

Constant Field Values

PROP_WINDOW_SHIFT_MS

@S4Double(defaultValue=10.0)
public static final java.lang.String PROP_WINDOW_SHIFT_MS

The property for window shift in milliseconds, which has a default value of 10F.

See Also:

Constant Field Values

PROP_ALPHA

@S4Double(defaultValue=0.46)
public static final java.lang.String PROP_ALPHA

The property for the alpha value of the Window, which is the value for the RaisedCosineWindow.

See Also:

Constant Field Values

WINDOW_SHIFT_SAMPLES

public static final java.lang.String WINDOW_SHIFT_SAMPLES

See Also:

Constant Field Values

WINDOW_SIZE_SAMPLES

public static final java.lang.String WINDOW_SIZE_SAMPLES

See Also:

Constant Field Values

Constructor Detail

RaisedCosineWindower

public RaisedCosineWindower(double alpha,
                            float windowSizeInMs,
                            float windowShiftInMs)

RaisedCosineWindower

public RaisedCosineWindower()

Method Detail

newProperties

public void newProperties(PropertySheet ps)
                   throws PropertyException

Description copied from interface: Configurable

This method is called when this configurable component needs to be reconfigured.

Specified by:

newProperties in interface Configurable

Overrides:

newProperties in class ConfigurableAdapter

Parameters:

ps - a property sheet holding the new data

Throws:

PropertyException - if there is a problem with the properties.

initialize

public void initialize()

Description copied from class: BaseDataProcessor

Initializes this DataProcessor. This is typically called after the DataProcessor has been configured.

Specified by:

initialize in interface DataProcessor

Overrides:

initialize in class BaseDataProcessor

getData

public Data getData()
             throws DataProcessingException

Returns the next Data object, which is usually a window of the input Data, with the windowing function applied to it.

Specified by:

getData in interface DataProcessor

Specified by:

getData in class BaseDataProcessor

Returns:

the next available Data object, returns null if no Data object is available

Throws:

DataProcessingException - if a data processing error occurred

See Also:

Data

getWindowShiftInMs

public float getWindowShiftInMs()

Returns the shift size used to window the incoming speech signal. This value might be used by other components to determine the time resolution of feature vectors.

Returns:

the shift of the window

getSampleRate

public int getSampleRate()

roundToFrames

public long roundToFrames(long samples)

Rounds a given sample-number to the number of samples will be processed by this instance including the padding samples at the end..

Parameters:

samples - samples to round to

Returns:

rounded result