@patrickvonplaten would be awesome. I just found out that the
import librosa
import numpy as np

def resample(batch):
    batch["speech"] = librosa.resample(np.asarray(batch["speech"]), 48_000, 16_000)
    batch["sampling_rate"] = 16_000
    return batch

common_voice_train = common_voice_train.map(resample, num_proc=1)

was not really working. It takes very  (!) long even after 8  - 10 hours it hasn’t finished (and I’m using a very fast CPU).
I could test a fix - and fortunately I’ve found a 8TB HDD under the desk