> ## Documentation Index
> Fetch the complete documentation index at: https://docs.elata.bio/llms.txt
> Use this file to discover all available pages before exploring further.

# Signal Processing

> Band power analysis, FFT, and spectrum computation

## Band Powers

Compute standard EEG frequency band powers from a sample array:

```typescript theme={null}
import { initEegWasm, band_powers } from "@elata-biosciences/eeg-web";

await initEegWasm();

const powers = band_powers(samples, sampleRateHz);
// powers.delta  — 0.5–4 Hz
// powers.theta  — 4–8 Hz
// powers.alpha  — 8–13 Hz
// powers.beta   — 13–30 Hz
// powers.gamma  — 30–100 Hz
```

`band_powers` returns a `WasmBandPowers` object with named fields for each standard band.

***

## Individual Band Functions

For targeted analysis, use individual band functions:

```typescript theme={null}
import {
  alpha_power,
  beta_power,
  theta_power,
  delta_power,
  gamma_power,
  custom_band_power,
} from "@elata-biosciences/eeg-web";

const alpha = alpha_power(samples, sampleRateHz);
const beta = beta_power(samples, sampleRateHz);
const theta = theta_power(samples, sampleRateHz);
const delta = delta_power(samples, sampleRateHz);
const gamma = gamma_power(samples, sampleRateHz);

// Custom frequency range
const mu = custom_band_power(samples, sampleRateHz, 8.0, 12.0);
```

***

## Power Spectrum

Compute the full power spectrum via FFT:

```typescript theme={null}
import { compute_power_spectrum, get_fft_frequencies } from "@elata-biosciences/eeg-web";

const spectrum = compute_power_spectrum(samples, sampleRateHz);
const frequencies = get_fft_frequencies(samples.length, sampleRateHz);

// spectrum[i] is the power at frequencies[i] Hz
```

***

## Input Format

All signal processing functions expect:

| Parameter      | Type                         | Description                              |
| -------------- | ---------------------------- | ---------------------------------------- |
| `samples`      | `Float64Array` or `number[]` | Single-channel EEG time series           |
| `sampleRateHz` | `number`                     | Sampling rate in Hz (e.g., 256 for Muse) |

For multi-channel data (e.g., from `HeadbandFrameV1.eeg.samples`), extract individual channels and process them separately:

```typescript theme={null}
const frame: HeadbandFrameV1 = /* ... from transport ... */;
const channelIndex = 0; // TP9

const channelSamples = frame.eeg.samples.map(row => row[channelIndex]);
const powers = band_powers(new Float64Array(channelSamples), frame.eeg.sampleRateHz);
```