IoTDB-Quality

# STFT

# Usage

This function makes a short-time Fourier Transform (STFT) for input series. The input series is divided into several fix-width windows and performed Fourier transform. The amplitude of each frequency component is calculated.

Name: STFT

Input Series: Only support a single input series whose type is INT32 / INT64 / FLOAT / DOUBLE

Parameters:

  • nfft: The window size of STFT. The size of the last window may be smaller than it. By default, all values are regarded as a window.
  • beta: Quantization level. is quantized to . Its default value is 0. It only works when T_SNR is not given.
  • T_SNR: Target SNR. can be automatically determined with it.

Output Series: Ouput a single series whose type is DOUBLE. The timestamps are the same with the input.

# Example

Input series:

+-----------------------------+---------------+
|                         Time|root.test.d1.s1|
+-----------------------------+---------------+
|1970-01-01T08:00:00.000+08:00|            0.0|
|1970-01-01T08:00:01.000+08:00|            1.0|
|1970-01-01T08:00:02.000+08:00|            0.0|
|1970-01-01T08:00:03.000+08:00|           -1.0|
|1970-01-01T08:00:04.000+08:00|            0.0|
|1970-01-01T08:00:05.000+08:00|           -2.0|
|1970-01-01T08:00:06.000+08:00|            0.0|
|1970-01-01T08:00:07.000+08:00|            2.0|
+-----------------------------+---------------+

SQL for query:

select stft(s1,'nfft'='4') from root.test.d1

Output series:

+-----------------------------+---------------------------------+
|                         Time|stft(root.test.d1.s1, "nfft"="4")|
+-----------------------------+---------------------------------+
|1970-01-01T08:00:00.000+08:00|                              0.0|
|1970-01-01T08:00:01.000+08:00|                              1.0|
|1970-01-01T08:00:02.000+08:00|                              0.0|
|1970-01-01T08:00:03.000+08:00|                              0.0|
|1970-01-01T08:00:04.000+08:00|                              0.0|
|1970-01-01T08:00:05.000+08:00|                              2.0|
|1970-01-01T08:00:06.000+08:00|                              0.0|
|1970-01-01T08:00:07.000+08:00|                              0.0|
+-----------------------------+---------------------------------+

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