Data Format

EEG Frame

Every frame from the WebSocket is a JSON object:


{ "t": 1711234567.123, "n": 42, "channels": [12.34, -5.67, 8.90, ...] }

Field	Type	Description
`t`	`float`	Unix timestamp (seconds, 6-decimal precision)
`n`	`int`	Sample number (monotonic, incremental)
`channels`	`float[]`	µV per channel — 8 elements for `pieeg8` / `ironbci8`, 16 for `pieeg16` (default)

Frequency Bands

Band	Range	Color
Delta (δ)	0.5–4 Hz	`#8b5cf6` purple
Theta (θ)	4–8 Hz	`#06b6d4` cyan
Alpha (α)	8–13 Hz	`#22c55e` green
Beta (β)	13–30 Hz	`#f59e0b` amber
Gamma (γ)	30–100 Hz	`#ef4444` red

FFT Output

256-point Cooley-Tukey radix-2 FFT with Hanning window:

FFT Size: 256 samples ≈ 1.024 seconds at 250 Hz
Frequency resolution: 250 Hz / 256 = ~0.977 Hz per bin
Output bins: 129 frequency bins (0 to 125 Hz)
Output PSD: µV²/Hz (absolute units, not dB)

TypeScript Types

Core EEG


interface EEGData {
  buffers: MutableRefObject<Float32Array[]>;
  writeIndex: MutableRefObject<number>;
  samplesInBuffer: MutableRefObject<number>;
  bufferSize: number;
  numChannels: number;
  gridSuspended: boolean;
}
 
interface FFTResult {
  frequencies: Float64Array;
  psd: Float64Array;
  bandPowers: BandPowers;
  dominantFrequency: number;
  totalPower: number;
}
 
type BandPowers = Record<"Delta" | "Theta" | "Alpha" | "Beta" | "Gamma", number>;

Webhook Types


type TriggerType =
  | "band_power_above" | "band_power_below"
  | "amplitude_above" | "amplitude_below"
  | "band_ratio_above" | "band_ratio_below";
 
type Band = "delta" | "theta" | "alpha" | "beta" | "gamma";
 
interface WebhookRule {
  id: string;
  name: string;
  enabled: boolean;
  trigger_type: TriggerType;
  params: Record<string, unknown>;
  url: string;
  method: string;
  headers: Record<string, string>;
  cooldown: number;
  last_fired: number;
  fire_count: number;
}
 
interface WebhookEvent {
  rule_id: string;
  rule_name: string;
  trigger_type: string;
  value: number;
  threshold: number;
  ts: number;
}