进行音频和梅尔频谱图预处理： python pre.py <datasets_root> -d {dataset} -n {number}

**进行音频和梅尔频谱图预处理： python pre.py -d {dataset} -n {number}**
1、这一步是不是必须要执行，才能执行训练合成器？
2、是不是必须全量执行？ 可以选择部分 进行pre 吗？
3、如果期间中断，有方法继续按原有进度运行吗？

Start with the pre.py command shown in the issue and trace how its generated audio and mel-spectrogram data is consumed by the synthesizer training workflow. Document whether preprocessing is required, whether partial datasets are supported, and whether an interrupted run can resume; the answers should be grounded in the repository's current behavior.

Written by the indexing model from the issue text.