CODEWITHSUNDEEP
pythonnumpylibrosa
user10467738
user10467738

Reputation: 73

Obtaining the Log Mel-spectrogram in Python

Other questions such as How to convert a mel spectrogram to log-scaled mel spectrogram have asked how to get the log-scaled mel spectrogram in python. My code below produces said spectrogram

ps = librosa.feature.melspectrogram(y=y, sr=sr)
ps_db= librosa.power_to_db(ps, ref=np.max)
librosa.display.specshow(ps_db, x_axis='s', y_axis='log')

If I plot this, I get the spectrogram I am looking for.

Librosa Display Plot

However, if I don't use librosa's display.specshow and just perform

import matplotlib.pyplot as plt
plt.imshow(ps_db)

I get this

matplotlib plot

My question is, what transformation is display.specshow doing to produce the first plot and how can I recreate this just using ps_db and numpy such that my plt.imshow() call aligns with display.specshow?

Upvotes: 2

Views: 8790

Answers (1)

Dorian
Dorian

Reputation: 1488

As suggested in the comment, you need to change the origin to lower, change the colormap to magma (I guess; could also be "plasma" or "inferno", chose here)

import matplotlib.pyplot as plt

fig, ax = plt.figure()
plt.imshow(ps_db, origin="lower", cmap=plt.get_cmap("magma"))

Regarding the logarithmic scale, as far as I can see, the data you get is already in logarithmic scale, just the ticks are wrong. If that is not the case, the you need to resample the data with a meshgrid adapted from here:

h, w = ps_db.shape
x = np.linspace(0, 2, w)
y = np.logspace(1, 8, h)
X, Y = np.meshgrid(x,y)

Upvotes: 2

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