3. Working with Effects (AudioNodes)

GainNode

acts as an “audio mixer”
represents a change in volume (volume control)
single input and single output, multiplying the input audio signal by the gain attribute

var audioContext = new AudioContext();
var gainNode = audioContext.createGain();
source.connect(gainNode);
gainNode.connect(audioContext.destination);

BiquadFilterNode

audio processing module
low-order filter
created using AudioContext.createBiquadFilter()
connected via biquadFilter.connect(audioContext.destination);
base for tone controls (bass, mid, treble), graphic equalizers and advanced filters
can be combined to form complex filters
default filter is lowpass (cutting high frequencies)
frequency default value is 350Hz
frequency ranges from 10Hz to half the Nyquist frequency

Nyquist Frequency

half the sample-rate of a discrete signal processing system

Properties:

BiquadFilterNode.frequency: k-rate AudioParam, representing a frequency in the current filtering algorithm (Hz)
BiquadFilterNode.detune: a-rate AudioParam, representing detuning of the frequency (Cents)
BiquadFilterNode.Q : k-rate AudioParam, representing a Q-factor (bandwidth - higher Q value, thinner and sharper peak. vice versa)
BiquadFilterNode.gain: k-rate AudioParam, representing gain used in current filtering algorithm
BiquadFilterNode.type: string value defining the kind of filtering algorithm the node is implementing

Parameters (type of filters)

lowpass: 12dB/octave rolloff. Frequencies below cutoff passes through, frequencies above are attenuated
highpass: 12dB/octave rolloff. Frequencies below cutoff are attenuated, frequencies above it pass through
bandpass: Frequencies outside the given range of frequencies are attenuated, frequencies within it pass through. Width of frequency band is adjusted by Q value. Greater Q value, smaller the frequency band
notch: opposite of bandpass filter. Frequencies outside the given range of frequencies pass through, frequencies within it are attenuated. Width of frequency band is adjusted by Q value as well
lowshelf: Frequenies lower than the frequency get a boost or attenuation
highshelf: Frequencies higher than the frequency get a boost or attenuation
peaking: Frequencies inside the range get a boost or attenuation
allpass: lets all frequencies through, changes phase-relationship between various frequencies

Parameter Automation

define a mapping from time to value
adds a new event into the list of a type specific to the method
kept in time-order in the list
new event will replace previous event of same type, if not it’ll be placed in the list after the previous
setValueAtTime() - SetValue
linearRampToValueAtTime() - LinearRampToValue
exponentialRampToValueAtTime() - ExponentialRampToValue
setTargetAtTime() - SetTarget
setValueCurveAtTime() - SetValueCurve

Dry/Wet Connections

Dry = raw
Wet = processed
goes under the gainNode, as it acts as an “audio mixer”
by creating a masterDry gain and a masterWet gain:
masterDry = context.createGain();
masterWet = context.createGain();

LINKS: