HARK version 1.1.0 Document : Synthesize

6.7.12 Synthesize

Outline of the node

This node converts signals of frequency domain into waveforms of time domain.

Necessary files

No files are required.

Usage

This node is used to convert signals of frequency domain into waveforms of time domain.

When to use

$\includegraphics[width=\linewidth ]{fig/modules/Synthesize}$

Figure 6.95: Example of a connection of Synthesize

Input-output and properties of the node

Table 6.69: Parameters of Synthesize

Parameter name	Type	Default value	Unit	Description
LENGTH	`int`	512	[pt]	FFT length
ADVANCE	`int`	160	[pt]	Shift length
SAMPLING_RATE	`int`	16000	[Hz]	Sampling rate
MIN_FREQUENCY	`int`	125	[Hz]	Minimum frequency
MAX_FREQUENCY	`int`	7900	[Hz]	Maximum frequency
WINDOW	`string`	HAMMING		Window function
OUTPUT_GAIN	`float`	1.0		Output gain

Input

INPUT: Map<int, ObjectRef> type. ObjectRef is Vector<complex<float> > .

Output

OUTPUT: Map<int, ObjectRef> type. ObjectRef is Vector<float> .

Parameter

LENGTH: FFT length; must be equal to the other node (MultiFFT ).
ADVANCE: Shift length; must be equal to the other node (MultiFFT ).
SAMPLING_RATE: Sampling rate; must be equal to the other nodes.
MIN_FREQUENCY: The minimum frequency used for waveform generation
MAX_FREQUENCY: The maximum frequency used for waveform generation
WINDOW: Window function. Select HAMMING, RECTANGLE or CONJ
OUTPUT_GAIN: Output gain

Details of the node

Inverse FFT is performed on four low bands of the input signals of the frequency domain by substituting 0 for frequency bins over $\omega _ s/2-100$ [Hz]. A designated window is adopted for overlap-add processing, a method of reducing the influence of a window by performing inverse transformation for every frame, adding the signals for which the time domains are shifted back while shifting them. For details, see the web pages in References. Finally, the temporal waveforms are multiplied by the output gain and output. Further, subsequent frames must be read for overlap-add processing; therefore, this node delays the entire processor. The length of the delay can be calculated as

$\begin{equation} delay = \left\{ \begin{array}{@{\, }ll} \left| \mathrm{LENGTH}/\mathrm{ADVANCE} \right|- 1,& \mbox{if~ ~ } \mathrm{LENGTH} \, mod\, \mathrm{ADVANCE} \undefined 0,\\ \mathrm{LENGTH}/\mathrm{ADVANCE}, & \mbox{otherwise}. \end{array} \right. \end{equation}$

(134)

Since the default values for HARK are LENGTH = 512 and ADVANCE = 160, the delay is three frames, which resulting in a 30 [ms] delay for the entire system.

References

(1) http://en.wikipedia.org/wiki/Overlap-add