Comparison of spectrogram between librosa and torchlibrosa

[ChrisNick92]

Hello everyone and good job for this library.

I am trying to figure out the correspondence between librosa and torchlibrosa for the spectrogram extraction.
As stated in the description, Spectrogram method of torchlibrosa corresponds to the stft method of librosa.

I created the following script to check if this true but I get different results:

import numpy as np
import librosa
import torchlibrosa as tl
import torch

if __name__ == "__main__":

    # Sample audio of 8KHz
    audio = np.random.randn(1, 8_000).astype(np.float32)

    # Extract Spectrogram Amplitude with Librosa
    Specl = np.squeeze(np.abs(librosa.stft(y=audio, n_fft=1024, hop_length=256)))
    # Shape: (Freq bins x Time bins)
    print(f"Librosa spec shape: {Specl.shape}")

    # Extract Spectrogram Amplitude with TL
    spec_extractor = tl.Spectrogram(n_fft=1024, hop_length=256, power=1)
    Spectl = torch.squeeze(spec_extractor(torch.from_numpy(audio))).T
    # Shape (Freq bins x Time bins)
    print(f"TorchLibrosa spec shape: {Spectl.shape}")

    # Compare
    print("\n\nLibrosa Spectrogram\n", Specl, "\n\n\n", "Torch Librosa Spectrogram\n", Spectl)
    Specl = torch.from_numpy(Specl)

    print(f"\nL infty norm of difference: {torch.abs(Specl - Spectl).max()}")

When I execute the above script with python librosa_comparison.py I get the following output:

Librosa spec shape: (513, 32)
TorchLibrosa spec shape: torch.Size([513, 32])


Librosa Spectrogram
 [[19.054897   1.9908019 17.752724  ... 12.835096  22.917797  10.363778 ]
 [20.790785  24.919458  24.746351  ... 25.476685  15.694681   5.6991477]
 [21.582727  18.81189   16.363668  ... 35.682972  10.927736   3.178584 ]
 ...
 [14.2219305 32.846138  41.570446  ... 15.117013   5.9180603 10.4871025]
 [ 9.384632  12.503995  30.297691  ... 10.411208   8.746181  13.068881 ]
 [ 7.3271813 19.286459  19.321154  ...  1.8899674 15.552687  15.774155 ]] 


 Torch Librosa Spectrogram
 tensor([[38.4898,  8.1263, 17.7527,  ..., 12.8351, 24.5029, 17.0312],
        [38.6057, 30.1623, 24.7463,  ..., 25.4767, 14.2940,  9.5362],
        [24.1956, 16.3059, 16.3637,  ..., 35.6830, 12.6571,  6.5012],
        ...,
        [24.0833, 35.3503, 41.5704,  ..., 15.1170,  6.7059, 10.9721],
        [18.3864,  9.4011, 30.2977,  ..., 10.4112,  8.4296, 19.5919],
        [14.2744, 22.7395, 19.3212,  ...,  1.8900, 17.0934, 27.0281]])

L infty norm of difference: 34.372806549072266

Is anything that I am doing wrong? What's the relation between Spectrogram method of torchlibrosa and stft of librosa.

Thanks in advance!