Librosa Display Waveplot, why are they totally blue and flat? - wav

Question

I followed this example of Music Synchronization with Dynamic Time Warping
However, when I do this:
import matplolib.pyplot as plt
import librosa
import librosa.display
x_1, fs = librosa.load('musicdata/slow_melody.wav')
plt.figure(figsize=(16, 4))
librosa.display.waveplot(x_1, sr=fs)
plt.title('Slower Version $X_1$')
plt.tight_layout()
and same for the faster version, I get this result:
I can properly reach the pitch classes of the wav files in chroma representations and there are no problems in the wav files.
I created the fast and slow versions of the wav files like this:
# Tone-duration sequence
melody = [('E', 0.3), ('E', 0.3), ('F', 0.3), ('G', 0.3)]
slow_melody = [('E', 0.6), ('E', 0.6), ('F', 0.6), ('G', 0.6)]
melody_output = np.array([])
# Construct the audio signal based on the chord sequence
for item in melody:
input_tone = item[0]
duration = item[1]
synthesized_tone = synthesizer(tone_freq_map[input_tone], duration, amplitude, sampling_freq)
melody_output = np.append(melody_output, synthesized_tone, axis=0)
# Write to the output file
name = 'melody' + '.wav'
write(name, sampling_freq, melody_output)
slow_melody_output = np.array([])
# Construct the audio signal based on the chord sequence
for item in slow_melody:
input_tone = item[0]
duration = item[1]
synthesized_tone = synthesizer(tone_freq_map[input_tone], duration, amplitude, sampling_freq)
slow_melody_output = np.append(slow_melody_output, synthesized_tone, axis=0)
# Write to the output file
name = 'slow_melody' + '.wav'
write(name, sampling_freq, slow_melody_output)
I get the tone frequencies from:
{
"A": 440,
"Asharp": 466,
"B": 494,
"C": 523,
"Csharp": 554,
"D": 587,
"Dsharp": 622,
"E": 659,
"F": 698,
"Fsharp": 740,
"G": 784,
"Gsharp": 831
}
Synthesizer is:
def synthesizer(freq, duration, amp=1.0, sampling_freq=44100):
# Build the time axis
t = np.linspace(0, duration, duration * sampling_freq)
# Construct the audio signal
audio = amp * np.sin(2 * np.pi * freq * t)
return audio.astype(np.int16)
Also, the input parameters are:
duration = 2
amplitude = 10000
sampling_freq = 44100
So, why couldn't I properly visualize the waveplots? What could be the reason that they appear like this?

Answer 1

I believe there is something wrong in the tutorial you are following. librosa.display.waveplot() doesn't plot anything by itself, you still have to call plt.show() to visualize it. From the official documentation, here's an example of it's usage:
y, sr = librosa.load(librosa.util.example_audio_file(), duration=10)
librosa.display.waveplot(y_harm, sr=sr, alpha=0.25)
plt.tight_layout()
plt.show()
You can find more info here https://librosa.github.io/librosa/generated/librosa.display.waveplot.html