Struct PreprocessingConfig 

pub struct PreprocessingConfig {
    pub highpass_cutoff_hz: f32,
    pub sample_rate_hz: u32,
    pub dc_bias_alpha: f32,
    pub enable_dc_removal: bool,
    pub enable_highpass: bool,
    pub highpass_order: HighpassOrder,
}

Configuration for DC offset removal and high-pass filtering.

Examples

use speech_prep::preprocessing::PreprocessingConfig;

// Default: 80 Hz high-pass, 16kHz sample rate, EMA α=0.95
let config = PreprocessingConfig::default();

// Custom configuration for noisy environment
let config = PreprocessingConfig {
    highpass_cutoff_hz: 120.0, // More aggressive low-frequency removal
    dc_bias_alpha: 0.98,       // Slower DC adaptation
    ..Default::default()
};

Fields

highpass_cutoff_hz: f32

High-pass filter cutoff frequency in Hz.

Range: 60.0 - 120.0 Default: 80.0

Effect: Frequencies below this cutoff are attenuated (≥20 dB at fc/2). Higher cutoffs remove more low-frequency content but may affect speech naturalness.

Recommendation:

• 60-80 Hz: Standard speech (default)
• 80-100 Hz: Noisy environments with HVAC/rumble
• 100-120 Hz: Extreme low-frequency noise

sample_rate_hz: u32

Audio sample rate in Hz.

Typical Values: 16000, 44100, 48000 Default: 16000

Effect: Determines filter coefficient calculation. Must match the actual sample rate of input audio.

dc_bias_alpha: f32

EMA smoothing factor for DC bias estimation.

Range: 0.9 - 0.99 Default: 0.95

Effect: Controls adaptation speed of DC bias tracking.

• Higher (0.95-0.99): Slower adaptation, smoother (recommended)
• Lower (0.90-0.94): Faster adaptation, less smooth

Formula: bias_new = α × bias_old + (1-α) × sample_mean

enable_dc_removal: bool

Enable DC offset removal stage.

Default: true

Effect: When false, DC removal is skipped (filter-only mode). Useful if audio is already DC-free (rare).

enable_highpass: bool

Enable high-pass filtering stage.

Default: true

Effect: When false, high-pass filter is skipped (DC-only mode). Useful for testing or if audio already high-pass filtered.

highpass_order: HighpassOrder

Order of the high-pass filter.

Default: FourthOrder (two cascaded biquads)

Effect: Higher order increases low-frequency attenuation at the cost of additional computation. FourthOrder meets the ≥20 dB @ 40 Hz target.

Implementations

impl PreprocessingConfig

pub fn validate(&self) -> Result<()>

Validate configuration parameters.

Errors

Returns Error::Configuration if:

• highpass_cutoff_hz < 20 Hz (too low, ineffective)
• highpass_cutoff_hz >= Nyquist frequency (fs/2)
• dc_bias_alpha not in (0.0, 1.0)
• sample_rate_hz is zero

Trait Implementations

impl Clone for PreprocessingConfig

fn clone(&self) -> PreprocessingConfig

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for PreprocessingConfig

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for PreprocessingConfig

fn default() -> Self

Returns the “default value” for a type.

impl Copy for PreprocessingConfig