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AnalyserNode

Namespace: SpawnDev.SpawnJS.JSObjects
Inheritance: SpawnJSObject -> EventTarget -> AudioNode -> AnalyserNode
MDN Reference: AnalyserNode

The AnalyserNode class provides real-time frequency and time-domain analysis information for audio visualizations. It passes audio through unchanged from input to output, but lets you read the generated data to create visual representations of the audio (spectrum analyzers, waveform displays, VU meters, etc.). Created via AudioContext.CreateAnalyser().

Constructors

Signature Description
AnalyserNode(SpawnJSObjectReference _ref) Deserialization constructor.

Properties

Property Type Description
FftSize ulong The FFT (Fast Fourier Transform) size. Must be a power of 2 between 32 and 32768. Default is 2048. Larger values give more frequency detail but less time resolution.
FrequencyBinCount ulong Read-only. Half of FftSize. This is the number of data values available for frequency visualization.
MinDecibels double Minimum power value in the scaling range for FFT data, used when converting to byte values. Default is -100.
MaxDecibels double Maximum power value in the scaling range for FFT data, used when converting to byte values. Default is -30.
SmoothingTimeConstant double Averaging constant with the last analysis frame. Range 0 to 1. Default is 0.8. Higher values produce smoother, less responsive visualizations.

Inherited Properties (from AudioNode)

Property Type Description
Context BaseAudioContext The associated audio context.
NumberOfInputs int Always 1.
NumberOfOutputs int Always 1. Audio passes through unchanged.
ChannelCount int Number of channels.

Methods

Analysis Methods

Method Return Type Description
GetByteFrequencyData(Uint8Array array) void Copies frequency data into a Uint8Array (0-255 range, scaled between MinDecibels and MaxDecibels). Array length should be FrequencyBinCount.
GetFloatFrequencyData(Float32Array array) void Copies frequency data into a Float32Array (decibel values). Array length should be FrequencyBinCount.
GetByteTimeDomainData(Uint8Array array) void Copies time-domain (waveform) data into a Uint8Array (0-255 range, 128 = silence). Array length should be FftSize.
GetFloatTimeDomainData(Float32Array array) void Copies time-domain (waveform) data into a Float32Array (-1.0 to 1.0 range). Array length should be FftSize.

Inherited Methods (from AudioNode)

Method Return Type Description
Connect(AudioNode node) AudioNode Connects output to another node.
Connect(AudioParam param) void Connects output to an AudioParam.
Disconnect() void Disconnects from all connected nodes.

Example

using var audioCtx = new AudioContext();
await audioCtx.Resume();

// Create an analyser for audio visualization
using var analyser = audioCtx.CreateAnalyser();
analyser.FftSize = 2048;
analyser.SmoothingTimeConstant = 0.85;
analyser.MinDecibels = -90;
analyser.MaxDecibels = -10;

Console.WriteLine($"Frequency bins: {analyser.FrequencyBinCount}"); // 1024

// Connect a source to the analyser
using var oscillator = audioCtx.CreateOscillator();
oscillator.Frequency.Value = 440;
oscillator.Connect(analyser);
analyser.Connect(audioCtx.Destination);
oscillator.Start();

// Read frequency data for a spectrum analyzer visualization
var bufferLength = (int)analyser.FrequencyBinCount;
using var frequencyData = new Uint8Array(bufferLength);

analyser.GetByteFrequencyData(frequencyData);
byte[] freqBytes = (byte[])frequencyData;
// Each element is 0-255, representing the amplitude at that frequency bin
for (int i = 0; i < 10; i++)
{
    Console.WriteLine($"Bin {i}: {freqBytes[i]}");
}

// Read time-domain data for a waveform/oscilloscope display
using var timeDomainData = new Float32Array((int)analyser.FftSize);

analyser.GetFloatTimeDomainData(timeDomainData);
float[] waveform = timeDomainData.ToArray();
// Each element is -1.0 to 1.0, representing the audio signal amplitude

// High-precision frequency analysis with Float32Array
using var floatFreqData = new Float32Array(bufferLength);
analyser.GetFloatFrequencyData(floatFreqData);
float[] freqFloats = floatFreqData.ToArray();
// Each element is in decibels (e.g., -90 to -10)

// Real-time visualization loop (use requestAnimationFrame)
// In Blazor, typically use a timer or animation frame callback:
void DrawVisualization()
{
    analyser.GetByteFrequencyData(frequencyData);
    byte[] data = (byte[])frequencyData;

    // Draw spectrum bars on a canvas
    for (int i = 0; i < bufferLength; i++)
    {
        float barHeight = data[i] / 255.0f; // Normalize to 0-1
        // ... draw bar at position i with height barHeight
    }
}

// Analyze microphone input
using var stream = await mediaDevices.GetUserMedia(
    new MediaStreamConstraints { Audio = true });
using var micSource = audioCtx.CreateMediaStreamSource(stream);
micSource.Connect(analyser);
// Don't connect analyser to destination to avoid feedback!