Class BiQuadFilter

Namespace

NAudio.Dsp

Assembly

NAudio.Core.dll

BiQuad filter

public class BiQuadFilter

Inheritance

object

BiQuadFilter

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

object.ToString()

Methods

AllPassFilter(float, float, float)

Creates an all pass filter

public static BiQuadFilter AllPassFilter(float sampleRate, float centreFrequency, float q)

Parameters

sampleRate float

Sample Rate

centreFrequency float

Centre Frequency

q float

Q (quality factor). Controls how sharply the phase transitions around the centre frequency.

Returns

BiQuadFilter

BandPassFilterConstantPeakGain(float, float, float)

Create a bandpass filter with constant peak gain

public static BiQuadFilter BandPassFilterConstantPeakGain(float sampleRate, float centreFrequency, float q)

Parameters

sampleRate float

Sample Rate

centreFrequency float

Centre Frequency

q float

Q (quality factor). Higher Q gives a narrower band; lower Q gives a wider band. Peak gain at the centre frequency is 0 dB regardless of Q.

Returns

BiQuadFilter

BandPassFilterConstantSkirtGain(float, float, float)

Create a bandpass filter with constant skirt gain

public static BiQuadFilter BandPassFilterConstantSkirtGain(float sampleRate, float centreFrequency, float q)

Parameters

sampleRate float

Sample Rate

centreFrequency float

Centre Frequency

q float

Q (quality factor). Higher Q gives a narrower band; lower Q gives a wider band. Peak gain at the centre frequency equals Q.

Returns

BiQuadFilter

HighPassFilter(float, float, float)

Create a High pass filter

public static BiQuadFilter HighPassFilter(float sampleRate, float cutoffFrequency, float q)

Parameters

sampleRate float

Sample Rate

cutoffFrequency float

Cut-off Frequency

q float

Q (quality factor). Use 1/sqrt(2) ≈ 0.707 for a Butterworth response (maximally flat passband, no peaking). The slope below the cutoff is ~12 dB/octave regardless of Q — cascade biquads in series for a steeper roll-off.

Returns

BiQuadFilter

HighShelf(float, float, float, float)

H(s) = A * (A*s^2 + (sqrt(A)/Q)*s + 1)/(s^2 + (sqrt(A)/Q)*s + A)

public static BiQuadFilter HighShelf(float sampleRate, float cutoffFrequency, float shelfSlope, float dbGain)

Parameters

sampleRate float

cutoffFrequency float

shelfSlope float

dbGain float

Returns

BiQuadFilter

LowPassFilter(float, float, float)

Create a low pass filter

public static BiQuadFilter LowPassFilter(float sampleRate, float cutoffFrequency, float q)

Parameters

sampleRate float

Sample Rate

cutoffFrequency float

Cut-off Frequency

q float

Q (quality factor). Use 1/sqrt(2) ≈ 0.707 for a Butterworth response (maximally flat passband, no peaking). The slope above the cutoff is ~12 dB/octave regardless of Q — cascade biquads in series for a steeper roll-off.

Returns

BiQuadFilter

LowShelf(float, float, float, float)

H(s) = A * (s^2 + (sqrt(A)/Q)s + A)/(As^2 + (sqrt(A)/Q)*s + 1)

public static BiQuadFilter LowShelf(float sampleRate, float cutoffFrequency, float shelfSlope, float dbGain)

Parameters

sampleRate float

cutoffFrequency float

shelfSlope float

a "shelf slope" parameter (for shelving EQ only).
When S = 1, the shelf slope is as steep as it can be and remain monotonically increasing or decreasing gain with frequency. The shelf slope, in dB/octave, remains proportional to S for all other values for a fixed f0/Fs and dBgain.

dbGain float

Gain in decibels

Returns

BiQuadFilter

NotchFilter(float, float, float)

Creates a notch filter

public static BiQuadFilter NotchFilter(float sampleRate, float centreFrequency, float q)

Parameters

sampleRate float

Sample Rate

centreFrequency float

Centre Frequency

q float

Q (quality factor). Higher Q gives a narrower notch; lower Q gives a wider notch.

Returns

BiQuadFilter

PeakingEQ(float, float, float, float)

Create a Peaking EQ

public static BiQuadFilter PeakingEQ(float sampleRate, float centreFrequency, float q, float dbGain)

Parameters

sampleRate float

Sample Rate

centreFrequency float

Centre Frequency

q float

Q (quality factor). Higher Q gives a narrower peak around the centre frequency; lower Q gives a wider, gentler bell.

dbGain float

Gain in decibels

Returns

BiQuadFilter

ResetState()

Clears the filter's sample history (the x/y delay elements) without changing its coefficients, so the next input is filtered as if from silence. Use when reusing a filter on a new, unrelated signal (e.g. an effect's Reset()).

public void ResetState()

SetHighPassFilter(float, float, float)

Set this as a high pass filter

public void SetHighPassFilter(float sampleRate, float cutoffFrequency, float q)

Parameters

sampleRate float

Sample Rate

cutoffFrequency float

Cut-off Frequency

q float

Q (quality factor). Use 1/sqrt(2) ≈ 0.707 for a Butterworth response (maximally flat passband, no peaking) — the recommended default for a clean high-pass. Larger values produce a resonant peak at the cutoff; smaller values give a more gradual roll-off into the cutoff. The slope below the cutoff is ~12 dB/octave regardless of Q — cascade biquads in series for a steeper roll-off.

SetLowPassFilter(float, float, float)

Set this up as a low pass filter

public void SetLowPassFilter(float sampleRate, float cutoffFrequency, float q)

Parameters

sampleRate float

Sample Rate

cutoffFrequency float

Cut-off Frequency

q float

Q (quality factor). Use 1/sqrt(2) ≈ 0.707 for a Butterworth response (maximally flat passband, no peaking) — the recommended default for a clean low-pass. Larger values produce a resonant peak at the cutoff; smaller values give a more gradual roll-off into the cutoff. The slope above the cutoff is ~12 dB/octave regardless of Q — cascade biquads in series for a steeper roll-off.

SetPeakingEq(float, float, float, float)

Set this up as a peaking EQ

public void SetPeakingEq(float sampleRate, float centreFrequency, float q, float dbGain)

Parameters

sampleRate float

Sample Rate

centreFrequency float

Centre Frequency

q float

Q (quality factor). Higher Q gives a narrower peak around the centre frequency; lower Q gives a wider, gentler bell.

dbGain float

Gain in decibels

Transform(ReadOnlySpan<float>, Span<float>)

Passes a block of samples through the filter. Equivalent to — and produces byte-identical output to — calling Transform(float) on each element of source in order, but keeps the coefficients and state variables in locals so the JIT can hold them in registers across the loop.

public void Transform(ReadOnlySpan<float> source, Span<float> destination)

Parameters

source ReadOnlySpan<float>

Input samples.

destination Span<float>

Output samples. May be the same span as source (in-place filtering) or a separate buffer at least as long as source.

Remarks

A biquad has a forward-only dependency (the next output depends on previous inputs AND outputs), so the inner loop can't be vectorised; the speedup over the single-sample form comes entirely from not having to reload field values each iteration.

Transform(float)

Passes a single sample through the filter

public float Transform(float inSample)

Parameters

inSample float

Input sample

Returns

float

Output sample

UpdateBandPassFilter(float, float, float)

Retunes this filter as a band-pass (constant 0 dB peak gain) without clearing its delay state, so it can be modulated per block/sample without a click.

public void UpdateBandPassFilter(float sampleRate, float centreFrequency, float q)

Parameters

sampleRate float

Sample rate.

centreFrequency float

New centre frequency.

q float

New Q (quality factor).

UpdateHighPassFilter(float, float, float)

Retunes this filter as a high-pass without clearing its delay state, so it can be modulated per block/sample without the click SetHighPassFilter(float, float, float) causes.

public void UpdateHighPassFilter(float sampleRate, float cutoffFrequency, float q)

Parameters

sampleRate float

Sample rate.

cutoffFrequency float

New cut-off frequency.

q float

New Q (quality factor).

UpdateLowPassFilter(float, float, float)

Retunes this filter to a new low-pass cutoff and Q without clearing its sample history, so a running filter can be modulated every sample/block (e.g. a synth filter envelope or LFO, an auto-wah) without the click that SetLowPassFilter(float, float, float) causes by resetting state. Use only on an already-running, non-divergent filter; for a fresh filter or after a seek use SetLowPassFilter(float, float, float) (or ResetState()) so latched NaN/Infinity can't survive.

public void UpdateLowPassFilter(float sampleRate, float cutoffFrequency, float q)

Parameters

sampleRate float

Sample rate.

cutoffFrequency float

New cut-off frequency.

q float

New Q (quality factor).

UpdateNotchFilter(float, float, float)

Retunes this filter as a notch (band-reject) without clearing its delay state, so it can be modulated per block/sample without a click.

public void UpdateNotchFilter(float sampleRate, float centreFrequency, float q)

Parameters

sampleRate float

Sample rate.

centreFrequency float

New centre frequency.

q float

New Q (quality factor).