TimeStretch

Added in v0.2.0

Change the speed or duration of the signal without changing the pitch. This transform employs librosa.effects.time_stretch under the hood to achieve the effect.

Under the hood this uses phase vocoding. Note that phase vocoding can degrade audio quality by "smearing" transient sounds, altering the timbre of harmonic sounds, and distorting pitch modulations. This may result in a loss of sharpness, clarity, or naturalness in the transformed audio, especially when the rate is set to an extreme value.

If you need a better sounding time stretch method, consider the following alternatives:

• atempo in ffmpeg
• Rubber Band library
• https://github.com/KAIST-MACLab/PyTSMod
• https://github.com/vinusankars/ESOLA

Input-output example

In this example we speed up a sound by 25%. This corresponds to a rate of 1.25.

Input sound	Transformed sound

Usage example

from audiomentations import TimeStretch

transform = TimeStretch(
    min_rate=0.8,
    max_rate=1.25,
    leave_length_unchanged=True,
    p=1.0
)

augmented_sound = transform(my_waveform_ndarray, sample_rate=16000)

TimeStretch API

min_rate: float • range: [0.1, 10.0]

Default: 0.8. Minimum rate of change of total duration of the signal. A rate below 1 means the audio is slowed down.

max_rate: float • range: [0.1, 10.0]

Default: 1.25. Maximum rate of change of total duration of the signal. A rate greater than 1 means the audio is sped up.

leave_length_unchanged: bool

Default: True. The rate changes the duration and effects the samples. This flag is used to keep the total length of the generated output to be same as that of the input signal.

p: float • range: [0.0, 1.0]

Default: 0.5. The probability of applying this transform.