# 变换

Signal Processing Toolbox™ 提供的函数可用于计算广泛使用的正变换和逆变换，包括快速傅里叶变换 (FFT)、离散余弦变换 (DCT) 和沃尔什-哈达玛变换。提取信号包络并使用分析信号估计瞬时频率。在时频域中分析信号。研究幅值-相位关系，估计基频，并使用倒频谱检测频谱周期性。使用二阶格兹尔算法计算离散傅里叶变换。

## 函数

 `abs` 绝对值和复数的模 `angle` 相位角 `fft` 快速傅里叶变换 `ifft` 快速傅里叶逆变换 `fftshift` 将零频分量移到频谱中心 `ifftshift` 逆零频平移 `dftmtx` 离散傅里叶变换矩阵 `fft2` 二维快速傅里叶变换 `ifft2` 二维快速傅里叶逆变换 `instfreq` Estimate instantaneous frequency `czt` Chirp Z-transform `goertzel` Discrete Fourier transform with second-order Goertzel algorithm `dct` Discrete cosine transform `idct` Inverse discrete cosine transform
 `envelope` 信号包络 `fwht` Fast Walsh-Hadamard transform `ifwht` Inverse Fast Walsh-Hadamard transform `hilbert` 使用希尔伯特变换的离散时间解析信号
 `emd` Empirical mode decomposition `fsst` Fourier synchrosqueezed transform `ifsst` Inverse Fourier synchrosqueezed transform `hht` Hilbert-Huang transform `pspectrum` Analyze signals in the frequency and time-frequency domains `spectrogram` Spectrogram using short-time Fourier transform `xspectrogram` Cross-spectrogram using short-time Fourier transforms `stft` Short-time Fourier transform `dlstft` Deep learning short-time Fourier transform (自 R2021a 起) `stftLayer` Short-time Fourier transform layer (自 R2021b 起) `istftLayer` Inverse short-time Fourier transform layer (自 R2024a 起) `stftmag2sig` Signal reconstruction from STFT magnitude (自 R2020b 起) `istft` Inverse short-time Fourier transform `dlistft` Deep learning inverse short-time Fourier transform (自 R2024a 起) `vmd` Variational mode decomposition (自 R2020a 起) `wvd` Wigner-Ville distribution and smoothed pseudo Wigner-Ville distribution `xwvd` Cross Wigner-Ville distribution and cross smoothed pseudo Wigner-Ville distribution
 `cceps` Complex cepstral analysis `icceps` Inverse complex cepstrum `rceps` Real cepstrum and minimum-phase reconstruction
 `bitrevorder` Permute data into bit-reversed order `digitrevorder` Permute input into digit-reversed order