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HamDigiSharp — Real-Time Decoding

RealTimeDecoder wraps a DecoderEngine and handles all the plumbing for continuous audio capture: it accumulates raw samples, aligns period boundaries to the UTC clock, resamples if needed, and fires PeriodDecoded after each period.

Basic setup

using HamDigiSharp.Engine;
using HamDigiSharp.Models;

var engine = new DecoderEngine();
engine.Configure(new DecoderOptions
{
    MyCall       = "W1AW",
    DecoderDepth = DecoderDepth.Normal,
    ApDecode     = true,
});

using var rt = new RealTimeDecoder(engine, DigitalMode.FT8, captureRate: 48000)
{
    FreqLow    = 200,
    FreqHigh   = 3000,
    AlignToUtc = true,   // pad first window to the next UTC period boundary
};

rt.PeriodDecoded += (results, windowStart) =>
{
    foreach (var r in results)
        Console.WriteLine($"{windowStart:HH:mm:ss}  {r.Snr,4:+#;-#;0} dB  {r.FrequencyHz,6:F0} Hz  {r.Message}");
};

// Feed audio from your capture callback
void OnAudioData(float[] chunk) => rt.AddSamples(chunk);

Resampling

RealTimeDecoder accepts any captureRate and resamples internally to the mode's native rate (12 000 Hz or 11 025 Hz). Common capture rates 8 000–96 000 Hz are all supported via the Resampler (polyphase FIR).

Changing modes at runtime

rt.ChangeMode(DigitalMode.JT65A, captureRate: 48000);
// Clears internal buffers; next AddSamples call starts a fresh period

Transmission timing

When AlignToUtc = true, RealTimeDecoder waits until the next UTC period boundary before it begins accumulating the first decode window. Subsequent periods follow immediately with no gaps.

NextPeriodStart(DateTimeOffset.UtcNow) on the protocol object gives the exact UTC DateTimeOffset when the next TX window opens — useful for scheduling audio playback:

IProtocol proto = ProtocolRegistry.Get(DigitalMode.FT8);
DateTimeOffset txAt = proto.NextPeriodStart(DateTimeOffset.UtcNow);

// Schedule audio output to start exactly at txAt
scheduler.PlayAt(audio, txAt);

RealTimeDecoder properties

Property Type Default Description
FreqLow double 200 Lower edge of decode window (Hz)
FreqHigh double 3000 Upper edge of decode window (Hz)
AlignToUtc bool true Align first window to UTC period boundary

Disposal

RealTimeDecoder is IDisposable. The underlying DecoderEngine is not disposed when RealTimeDecoder is disposed — you own and dispose it separately:

using var engine = new DecoderEngine();
using var rt     = new RealTimeDecoder(engine, DigitalMode.FT8, captureRate: 48000);
// …
// rt is disposed first, engine second (both at end of using block or explicit Dispose)