audiomentions is a very convenient library for my bird sound classification. As the code below:

from audiomentations import Compose, AddGaussianNoise, AddGaussianSNR, TimeStretch, PitchShift

        self.augment = Compose([
            AddGaussianNoise(min_amplitude=0.005, max_amplitude=0.015, p=poss),
            AddGaussianSNR(min_snr_in_db=5.0, max_snr_in_db=40.0, p=poss),
            TimeStretch(min_rate=0.8, max_rate=1.2, p=poss),
            PitchShift(min_semitones=-2, max_semitones=2, p=poss)

These four augmentation methods are enough for current training. But the PitchShift method will cost a lot of CPU resources therefore the GPU couldn’t run to full load and the CPU usage jumps to 100%.

Failed to find an audio augmentation library that uses GPU, I started to check the source code of “audiomentions” and noticed that it uses librosa as its implementation:

            pitch_shifted_samples = librosa.effects.pitch_shift(
                samples, sr=sample_rate, n_steps=self.parameters["num_semitones"]
        except librosa.util.exceptions.ParameterError:

Then the code of “librosa” for “pitch_shift”:

def pitch_shift(
    y: np.ndarray,
    sr: float,
    n_steps: float,
    bins_per_octave: int = 12,
    res_type: str = "soxr_hq",
    scale: bool = False,
    **kwargs: Any,
) -> np.ndarray:

The default “res_type” for “pitch_shift” is “soxr_hq”. This is a slow resource. After changing “it”res_type” to “linear” in “audiomentions”, the CPU usage jumps back to 50% on my desktop and the GPU ramps up to 100% when training.

—— 2023.07.28 ——

Thanks for the correction from Iver.

After I run this test snippet:

import time
import librosa

sound, sr = librosa.load("./song/background/AirportAnnouncements_1.wav")

for resource in [None, "linear", "soxr_hq", "kaiser_best"]:
    begin = time.time()
    for _ in range(10):
        if resource:
            librosa.effects.pitch_shift(sound, sr=sr, n_steps=1, res_type=resource)
            librosa.effects.pitch_shift(sound, sr=sr, n_steps=1)
    if resource:
        print(f"{resource} time:", time.time() - begin)
        print("default time:", time.time() - begin)

and got the result

default time: 8.455572366714478
linear time: 3.3037502765655518
soxr_hq time: 3.3474862575531006
kaiser_best time: 8.467342615127563

Iver is right: the soxr_hq is as fast as linear. And the actual default res_type of librosa which I was using is kaiser_best.