webaudio.lib

An implementation of the WebAudio API filters (https://www.w3.org/TR/webaudio/). Its official prefix is wa.

This library implement WebAudio filters, using their C++ version as a starting point, taken from Mozilla Firefox implementation.

References

• https://github.com/grame-cncm/faustlibraries/blob/master/webaudio.lib

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BiquadFilter

Environment holding the normalized biquad coefficient sets (b0,b1,b2,a1,a2, ready for fi.tf2) of the Web Audio filters below, computed from the Web Audio API specification formulas.

Usage

BiquadFilter(f0, dBgain, Q, aDetune).lowpass2 // or .highpass2, .bandpass2,
                   // .notch2, .allpass2, .peaking2, .lowshelf2, .highshelf2

Where:

• f0: center/cutoff frequency in Hz
• dBgain: gain in dB (used by the peaking and shelving filters)
• Q: quality factor
• aDetune: detune amount in cents

Test

wa = library("webaudio.lib");
BiquadFilter_test = wa.BiquadFilter(1000, 6, 1, 0).lowpass2;

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(wa.)lowpass2

Standard second-order resonant lowpass filter with 12dB/octave rolloff. Frequencies below the cutoff pass through, frequencies above it are attenuated.

Usage

_ : lowpass2(f0, Q, dtune) : _

Where:

• f0: cutoff frequency in Hz
• Q: the quality factor
• dtune: detuning of the frequency in cents

Test

wa = library("webaudio.lib");
os = library("oscillators.lib");
lowpass2_test = os.osc(440) : wa.lowpass2(1000, 0.707, 0);

References

• https://searchfox.org/mozilla-central/source/dom/media/webaudio/blink/Biquad.cpp#98

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(wa.)highpass2

Standard second-order resonant highpass filter with 12dB/octave rolloff. Frequencies below the cutoff are attenuated, frequencies above it pass through.

Usage

_ : highpass2(f0, Q, dtune) : _

Where:

• f0: cutoff frequency in Hz
• Q: the quality factor
• dtune: detuning of the frequency in cents

Test

wa = library("webaudio.lib");
os = library("oscillators.lib");
highpass2_test = os.osc(440) : wa.highpass2(1000, 0.707, 0);

References

• https://searchfox.org/mozilla-central/source/dom/media/webaudio/blink/Biquad.cpp#127

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(wa.)bandpass2

Standard second-order bandpass filter. Frequencies outside the given range of frequencies are attenuated, the frequencies inside it pass through.

Usage

_ : bandpass2(f0, Q, dtune) : _

Where:

• f0: cutoff frequency in Hz
• Q: the quality factor
• dtune: detuning of the frequency in cents

Test

wa = library("webaudio.lib");
os = library("oscillators.lib");
bandpass2_test = os.osc(440) : wa.bandpass2(1000, 1, 0);

References

• https://searchfox.org/mozilla-central/source/dom/media/webaudio/blink/Biquad.cpp#334

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(wa.)notch2

Standard notch filter, also called a band-stop or band-rejection filter. It is the opposite of a bandpass filter: frequencies outside the give range of frequencies pass through, frequencies inside it are attenuated.

Usage

_ : notch2(f0, Q, dtune) : _

Where:

• f0: cutoff frequency in Hz
• Q: the quality factor
• dtune: detuning of the frequency in cents

Test

wa = library("webaudio.lib");
os = library("oscillators.lib");
notch2_test = os.osc(440) : wa.notch2(1000, 1, 0);

References

• https://searchfox.org/mozilla-central/source/dom/media/webaudio/blink/Biquad.cpp#301

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(wa.)allpass2

Standard second-order allpass filter. It lets all frequencies through, but changes the phase-relationship between the various frequencies.

Usage

_ : allpass2(f0, Q, dtune) : _

Where:

• f0: cutoff frequency in Hz
• Q: the quality factor
• dtune: detuning of the frequency in cents

Test

wa = library("webaudio.lib");
os = library("oscillators.lib");
allpass2_test = os.osc(440) : wa.allpass2(1000, 1, 0);

References

• https://searchfox.org/mozilla-central/source/dom/media/webaudio/blink/Biquad.cpp#268

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(wa.)peaking2

Frequencies inside the range get a boost or an attenuation, frequencies outside it are unchanged.

Usage

_ : peaking2(f0, gain, Q, dtune) : _

Where:

• f0: cutoff frequency in Hz
• gain: the gain in dB
• Q: the quality factor
• dtune: detuning of the frequency in cents

Test

wa = library("webaudio.lib");
os = library("oscillators.lib");
peaking2_test = os.osc(440) : wa.peaking2(1000, 3, 1, 0);

References

• https://searchfox.org/mozilla-central/source/dom/media/webaudio/blink/Biquad.cpp#233

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(wa.)lowshelf2

Standard second-order lowshelf filter. Frequencies lower than the frequency get a boost, or an attenuation, frequencies over it are unchanged.

Usage

_ : lowshelf2(f0, gain, dtune) : _

Where:

• f0: cutoff frequency in Hz
• gain: the gain in dB
• dtune: detuning of the frequency in cents

Test

wa = library("webaudio.lib");
os = library("oscillators.lib");
lowshelf2_test = os.osc(440) : wa.lowshelf2(500, 6, 0);

References

• https://searchfox.org/mozilla-central/source/dom/media/webaudio/blink/Biquad.cpp#169

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(wa.)highshelf2

Standard second-order highshelf filter. Frequencies higher than the frequency get a boost or an attenuation, frequencies lower than it are unchanged.

Usage

_ : highshelf2(f0, gain, dtune) : _

Where:

• f0: cutoff frequency in Hz
• gain: the gain in dB
• dtune: detuning of the frequency in cents

Test

wa = library("webaudio.lib");
os = library("oscillators.lib");
highshelf2_test = os.osc(440) : wa.highshelf2(2000, -6, 0);

References

• https://searchfox.org/mozilla-central/source/dom/media/webaudio/blink/Biquad.cpp#201