---
title: Analysis
description: "Live levels and spectra from an analyser, in the shape a meter or a plot reads, and the analysis functions behind them."
---

Tap a signal with an `AnalyserNode`, a tap that plays nothing, and these hooks turn it into a live [source](/docs/engine#your-own-engine) a component repaints from, with no React render per frame.

## Levels

```bash
npx shadcn@latest add @audio-ui/use-audio-levels
```

```tsx
import { useAudioLevels } from "@/hooks/use-audio-levels";

// One analyser per channel, made once: a new array restarts the sampling.
const analysers = useMemo(() => {
  const analyser = ctx.createAnalyser();
  output.connect(analyser);
  return [analyser];
}, [ctx, output]);

const levels = useAudioLevels(analysers);

<Meter aria-label="Output" source={levels} />;
```

`useAudioLevels(analysers)` gives `{ levels, peaks }`, one entry per analyser, in dB: the RMS level, which falls back smoothly as a needle would, and a peak that holds, then falls. A `ChannelSplitterNode` splits a stereo signal into one analyser per side. While the signal is silent, nothing is published. A [Meter](/docs/components/base/meter) paints it, and the [Mixer](/docs/components/base/mixer) gives one to each channel.

## Spectrum

```bash
npx shadcn@latest add @audio-ui/use-spectrum
```

```tsx
import { useSpectrum, useSpectrumPeaks } from "@/hooks/use-spectrum";

const analyser = ctx.createAnalyser();
analyser.fftSize = 8192; // finer low end
output.connect(analyser);

const spectrum = useSpectrum(analyser, { minHz: 20, maxHz: 20000 });
const peaks = useSpectrumPeaks(spectrum, { hold: 1, fall: 24 });

<SpectrumAnalyzer aria-label="Spectrum" peaks={peaks} source={spectrum} />;
```

`useSpectrum` gives dB per point along a logarithmic frequency axis, 160 points from 20 Hz to 20 kHz unless told otherwise. Draw it with the [Spectrum analyzer](/docs/components/base/spectrum-analyzer), or as a trace on a [Plot](/docs/components/base/plot) behind an equalizer's curve. `useSpectrumPeaks` keeps each point's loudest level for `hold` seconds, then lets it fall at `fall` dB per second.

## The functions behind them

`@audio-ui/core/analysis` holds the math as plain functions, for an engine of your own or a worker:

- `rmsDb(samples)`: The RMS level of samples, in dBFS.
- `dbToGain(db)`, `gainToDb(gain)`: dB and gain, both ways.
- `logSpectrum(bins, sampleRate, out, { minHz, maxHz })`: An analyser's bins on a log frequency axis, written into `out`.
- `holdPeaks(spectrum, peaks, holding, elapsed, { hold, fall })`: Held peaks, a frame at a time.
- `computePeaks(channels, buckets)`: A waveform's peaks, for a [Waveform](/docs/components/base/waveform).
- `formatDb(db)`, `formatHz(hz)`: A level and a frequency as text, such as "-6.0 dB" and "1.2 kHz".
- `biquadResponse`, `eqResponse`, `compressorOutput`: What a filter, an equalizer and a compressor do, to draw their curves.