signal_core 0.3.0

Format-agnostic multichannel signal engine: summary pyramids for fast zooming, display filters (SOS, zero-phase and streaming), re-referencing, channel quality and random-access byte sources. Pure Dar [...]

signal_core

signal_core is a signal engine for viewing large multichannel recordings and live streams. It is independent of any file format, pure Dart, and runs on all platforms, including the web. It provides the data handling behind signal_viewer and the indexed reading of large files in xdf.

API documentation

Installation

dart pub add signal_core

Components

Component	Purpose
SummaryPyramid	Minimum, maximum, mean and standard deviation over buckets of 64, 256, 1024… samples, so that a view of any length is drawn from a few thousand buckets
ChunkedSignalEngine	Answers EnvelopeRequests and ReadRequests for a recording that a format divides into chunks (ChunkedSignalIndex), with a bounded chunk cache, filtered tiles retained between requests, and derived (filtered, re-referenced) summaries built in the background
DerivedSpec, Sos, SosStreamFilter, applyReference, LiveProcessor	Display filters (zero-phase for recordings, streaming for live data), re-referencing and mean traces
QualityTracker	Per-channel flags for line noise, amplitude and flat channels
ByteSource	Random access to a file by path (native platforms), to a Blob (web) or to bytes in memory
SignalGenerator, SynthSpec, SynthRun	Synthetic test signals, reproducible from a seed, sent in real time with simulated dropouts, jitter and markers

The formats currently built on the engine are XDF, through the xdf package, and .hsd (libhyperscanner).

Synthetic signals

SignalGenerator produces multichannel test signals for exercising a display or processing pipeline. Each channel is the sum of components (waveforms, noise and artefacts), and the result depends only on the seed, so a test can compare output generated in chunks with output generated at once. SynthSpec builds the channels of a preset:

Preset	Content
sines	Channel n at n times the base frequency, wrapping below the Nyquist frequency, with white noise
testPattern	A different waveform on each channel: sine, square, sawtooth, chirp, DC, impulses, white, pink and line noise
eegResting	Pink noise, alpha bursts strongest on posterior channels, and a little line noise; 10-20 labels for up to 20 channels
eegArtefacts	eegResting with blinks strongest on frontal channels, spikes and drift; one channel clips and one is flat
lineNoise	A slow sine under strong 50 or 60 Hz interference and its harmonics
stress	A sine and white noise per channel, inexpensive to generate at high channel counts and rates

import 'package:signal_core/signal_core.dart';

void main() {
  final generator = const SynthSpec(
    preset: SynthPreset.eegArtefacts,
    channels: 16,
    rate: 500,
    seed: 1,
  ).generator();
  // One second of samples, interleaved by channel, and the blinks, spikes
  // and alpha bursts that began in it.
  final (values, events) = generator.next(500);
  print('${values.length} values, events: $events');
}

SynthRun sends a generator's samples as they fall due on a clock, with dropouts and time stamp jitter from Impairments and markers from MarkerSchedule. The LSL test outlets of lsl_tools and the synthetic source of signal_viewer are built on it.