M0LTE.Dsp 0.2.0

M0LTE.Dsp

Dependency-free digital-signal-processing primitives for .NET, extracted from the pdn-soundmodem packet-radio modem. Nothing here is radio-specific — it's general-purpose DSP (standard-API / textbook building blocks).

• Targets net10.0. No third-party package dependencies — just the BCL.
• Public API is locked by a build-time test and the package follows Semantic Versioning; see docs/versioning.md.

Install

dotnet add package M0LTE.Dsp

Quick start

using M0LTE.Dsp;

// Radix-2 FFT (in place, real/imaginary spans of equal power-of-2 length):
float[] re = new float[1024];
float[] im = new float[1024];
for (int i = 0; i < re.Length; i++)
    re[i] = MathF.Sin(2 * MathF.PI * 100 * i / re.Length); // a tone at bin 100
Fft.Forward(re, im);

// Anti-aliased ÷4 decimation, 48 kHz → 12 kHz:
var decimator = new Decimator(inputRate: 48000, factor: 4);
float[] input = new float[48000];
float[] output = new float[decimator.MaxOutput(input.Length)];
int produced = decimator.Process(input, output);

// Design a 1500 Hz low-pass FIR and stream samples through it:
var fir = new FirFilter(FilterDesign.LowPass(cutoffHz: 1500, sampleRate: 12000, taps: 96));
float y = fir.Next(0.5f);

// Occupied bandwidth (ITU-R SM.443), e.g. the 99 % OBW of a captured signal:
var (lowHz, highHz, widthHz, peakHz) = OccupiedBandwidth.Measure(output, sampleRate: 12000);

// SSB from an SDR's complex baseband: 48 kHz IQ in, 12 kHz USB audio out. Because you hold
// the baseband, the receive filter is yours to choose rather than a rig's to impose.
var ssb = new StreamingSsbDemodulator(new SsbDemodulatorOptions
{
    InputRate = 48000,
    OutputRate = 12000,
    Sideband = Sideband.Upper,
    DialHz = 0,               // the receiver is tuned to the dial, so the carrier is at DC
    SsbLowHz = 150, SsbHighHz = 3450,
});
short[] iq = new short[9600];                     // interleaved I,Q,I,Q…
float[] audio = new float[ssb.MaxOutputFor(iq.Length / 2)];
int wrote = ssb.Process(iq, audio);

(Exact constructor/method signatures are in the XML docs shipped with the package.)

Licence

AGPL-3.0-or-later (see LICENSE). The implementations are standard-API / textbook DSP — the design choices mirror QtSoundModem but no code was transcribed, so the package is permissively relicensable and is shipped AGPL-3.0-or-later by choice to match the M0LTE.* family. See PROVENANCE.md.