Speech Representations › Key Parameters
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The key parameters for the speech preprocessing pipeline are summarized in Table preprocessing-params.
| Parameter | Typical Value | Description |
|---|---|---|
| sr | 16000 Hz | Sample rate capturing frequencies up to 8 kHz |
| pre_emphasis | 0.97 | High-pass filter coefficient boosting high frequencies |
| n_fft | 512 | FFT points determining frequency resolution (bin width = sr/n_fft) |
| hop_length | 160 samples (10 ms) | Frame shift controlling temporal step between frames |
| win_length | 400 samples (25 ms) | Analysis window length affecting frequency resolution |
| n_mels | 80 | Number of mel frequency bins (40-128 typical range) |
| f_min | 0 Hz | Lower frequency bound for mel filterbank |
| f_max | 8000 Hz | Upper frequency bound for mel filterbank |
Higher sample rates preserve more high-frequency information but increase processing requirements linearly. Values closer to 1.0 for pre-emphasis provide a stronger high-frequency boost. Larger n_fft values provide finer frequency bins but reduce temporal localization. More mel bins provide finer frequency resolution but increase feature dimensionality. These parameters interact: increasing n_fft without increasing win_length amounts to zero-padding, which smooths the spectrum but does not add frequency resolution. Truly improving frequency resolution requires a longer analysis window, which in turn reduces temporal resolution. These constraints are basic and cannot be engineered away; the goal is choosing parameters that best serve the phonetic discrimination task given available compute.