Documentation
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Index ¶
Constants ¶
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Variables ¶
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Functions ¶
func EstimateCarrierOffsetHz ¶ added in v0.2.8
EstimateCarrierOffsetHz finds the dominant narrowband carrier offset in a complex baseband capture: the frequency (in Hz, positive = above centre) carrying the most averaged power within ±searchHz of DC. It is the single-carrier wrapper over EstimateCarrierCandidatesHz, preserving the original two-stage coarse+fine behaviour. Returns 0 for an empty input or zero searchHz.
func Mag2dB ¶ added in v0.4.3
Mag2dB converts a linear amplitude (magnitude) ratio to decibels (20·log10). Use it for an RMS or voltage figure; use Power2dB for a power figure. Values at or below zero clamp to -300 dB.
func Power2dB ¶ added in v0.4.3
Power2dB converts a linear power ratio to decibels (10·log10). Values at or below zero clamp to a floor of -300 dB rather than returning -Inf/NaN.
func RMS ¶ added in v0.4.3
RMS returns the root-mean-square amplitude of a complex baseband buffer: sqrt(mean(|x|^2)). For a full-scale complex sinusoid (|x| = 1) this is 1.0, so RMS in dBFS is 20·log10(RMS) (0 dBFS at full scale). It is the numpy `sqrt(mean(abs(x)**2))` capture-level power measure that no exported helper provided. Returns 0 for an empty buffer.
Types ¶
type AGC ¶
type AGC struct {
Reference float32 // target output magnitude (default 1.0)
Rate float32 // power-EMA coefficient (typical 1e-3 to 1e-2)
MaxGain float32 // ceiling that bounds the gain on near-silent input
// contains filtered or unexported fields
}
AGC normalises the average magnitude of a complex IQ stream toward Reference. It tracks signal power with an exponential moving average and applies that as a feed-forward scale, so an occasional near-zero sample — a linear-modulation symbol stream passes through the origin on π phase transitions — cannot spike the gain the way a per-sample feedback loop would.
type AudioAGC ¶
type AudioAGC struct {
// contains filtered or unexported fields
}
AudioAGC is the real-valued counterpart of AGC, sized for the post-demod chain in internal/voice/composer. The IQ-domain AGC drives the *complex* baseband magnitude toward a target with a single adaptation rate, which works because FM has a constant envelope on air. After demod the signal is voice — bursty, with short loud transients separated by quieter passages — so a single rate either pumps badly (too fast) or never catches up (too slow).
AudioAGC is a classic envelope-follower + gain stage:
abs = |x| if abs > level: level += (1 - α_attack) × (abs - level) // ramp up fast else: level += (1 - α_release) × (abs - level) // ramp down slow gain = clamp(reference / max(level, floor), 0, MaxGain) y[n] = x[n] × gain
Attack / release are time constants (in samples after construction); short attack catches transients before they clip, long release keeps the gain steady through speech gaps so the output doesn't pump. Reference is the target |y| ≈ Reference; pick something that leaves headroom for downstream stages (typical 0.3 keeps int16 conversion comfortably under MaxInt16 at the existing 10 000-scale in voice/composer).
AudioAGC is not safe for concurrent Process calls — pin it to a single demod goroutine and Reset between calls.
func NewAudioAGC ¶
func NewAudioAGC(cfg AudioAGCConfig) *AudioAGC
NewAudioAGC builds an envelope-follower-based AGC. Bad parameters trip a panic at startup so misconfiguration shows up loudly rather than silently producing wrong audio.
func (*AudioAGC) Gain ¶
Gain returns the current adaptive gain. Useful for diagnostics; not needed for normal operation.
type AudioAGCConfig ¶
type AudioAGCConfig struct {
Reference float32 // target |output| (default 0.3)
Attack time.Duration // ramp-up time constant (default 5 ms)
Release time.Duration // ramp-down time constant (default 200 ms)
MaxGain float32 // ceiling on adaptive gain (default 64.0)
SampleRate float64 // sample rate of the audio stream (Hz, required)
}
AudioAGCConfig configures NewAudioAGC. All time constants are in real time; the constructor folds in the sample rate.
type CarrierCandidate ¶ added in v0.4.3
CarrierCandidate is one detected narrowband carrier: its offset from DC (Hz, positive = above centre) and its averaged power relative to the strongest carrier in the band (dB, ≤ 0; the dominant carrier is 0 dB).
func EstimateCarrierCandidatesHz ¶ added in v0.4.3
func EstimateCarrierCandidatesHz(iq []complex64, sampleRateHz, searchHz, minSpacingHz float64, maxCandidates int) []CarrierCandidate
EstimateCarrierCandidatesHz returns up to maxCandidates carrier offsets in ±searchHz of DC, strongest first and each fine-refined. It generalises the single-peak EstimateCarrierOffsetHz so a control channel that is NOT the dominant carrier in a wideband capture can still be found and tried: a louder adjacent voice carrier no longer hides it. Coarse local maxima within minSpacingHz of an already-kept (stronger) candidate are suppressed, and candidates more than carrierCandidateFloorDb below the peak are dropped.
The search is the same bounded averaged periodogram as the single-carrier path (a Goertzel-style DFT, no full FFT): a coarse pass scores every bin across the band, local maxima are kept (spacing- and floor-gated), then each is refined with a fine pass around its coarse bin.
minSpacingHz ≤ 0 uses defaultCarrierMinSpacingHz; maxCandidates ≤ 0 uses defaultMaxCarrierCandidates. Returns nil for an empty input or zero searchHz.
type NCO ¶ added in v0.2.8
type NCO struct {
// contains filtered or unexported fields
}
NCO is a numerically-controlled oscillator for frequency-shifting a complex baseband stream — i.e. "tuning" a channel that sits at a non-zero offset down to 0 Hz. Mix multiplies each input sample by e^{-j·2π·offsetHz·n/Fs}, so a spectral component at +offsetHz lands at DC.
The phasor is generated recursively (one complex multiply per sample) rather than via a Cos/Sin call. Repeated float32 multiplies let the magnitude drift off the unit circle, so renorm folds it back every renormEveryN samples — one sqrt amortised over thousands of samples, well below the surrounding numeric noise floor.
This mirrors the private oscillator inside internal/dsp/tuner's DDC bank, exported here as a standalone primitive the replay path and the single-channel down-converter (ccdecoder.Downconverter) reuse to tune an off-centre recorded capture without standing up a whole tuner bank.
func NewNCO ¶ added in v0.2.8
NewNCO returns an oscillator that shifts a component at +offsetHz down to DC at the given sample rate. A zero offset yields an identity mix.
func (*NCO) Mix ¶ added in v0.2.8
Mix writes the frequency-shifted src into dst (reused when it has capacity) and returns it. src is not read after the matching dst element is written, so in-place operation (dst aliasing src) is safe.
type RealResampler ¶
type RealResampler struct {
L, M int
// contains filtered or unexported fields
}
RealResampler is the real-valued counterpart of Resampler. Same polyphase decomposition, same L/M rate, but operates on float32 audio instead of complex64 IQ. Sized for the post-demod chain in internal/voice/composer where the FM demod hands real audio to a resampler that retunes 48 kHz → 8 kHz (or arbitrary rational ratios) with proper anti-aliasing built into the polyphase prototype filter.
The complex Resampler stays where it is — IQ paths still want it. Splitting them keeps each loop hot on the right data type without the complex64 ↔ float32 conversion overhead that an interface would impose.
RealResampler is not safe for concurrent Process calls — pin it to a single demod goroutine and Reset between calls.
func NewRealResampler ¶
func NewRealResampler(L, M, tapsPerBranch int, beta float64) *RealResampler
NewRealResampler builds a real-valued resampler with rate L/M using a Kaiser-window LPF of total length tapsPerBranch*L. Cutoff is min(0.5/L, 0.5/M) so the prototype rejects images and aliases for both the interpolation and decimation steps. Bad parameters trip a panic at construction so misconfiguration shows up loudly.
func (*RealResampler) Process ¶
func (r *RealResampler) Process(dst, src []float32) []float32
Process consumes len(src) input samples and returns approximately len(src)*L/M output samples. dst is reused if it has capacity.
func (*RealResampler) Reset ¶
func (r *RealResampler) Reset()
Reset clears the running history and commutator state so the next Process call starts from silence.
type Resampler ¶
type Resampler struct {
L, M int
// contains filtered or unexported fields
}
Resampler is a polyphase rational resampler with rate L/M. It interpolates by L (using polyphase branches of an LPF) and decimates by M.
func NewResampler ¶
NewResampler builds a resampler with rate L/M using a Kaiser-window LPF of total length tapsPerBranch*L. Cutoff is min(0.5/L, 0.5/M) so that the filter rejects images and aliases for both interpolation and decimation.
Source Files
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Directories
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| Path | Synopsis |
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Package blind estimates the symbol/baud rate and a coarse modulation class of an unknown carrier directly from its channelized IQ, with no protocol decoder.
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Package blind estimates the symbol/baud rate and a coarse modulation class of an unknown carrier directly from its channelized IQ, with no protocol decoder. |
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Package channelizer implements an M-channel critically-sampled polyphase channelizer.
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Package channelizer implements an M-channel critically-sampled polyphase channelizer. |
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Package demod contains baseband demodulators that convert IQ streams into real-valued symbol streams (or audio, for FM).
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Package demod contains baseband demodulators that convert IQ streams into real-valued symbol streams (or audio, for FM). |
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Package diag provides developer/diagnostic helpers — IQ-sample decimation, energy + bandwidth estimation — that feed the web console's Constellation panel.
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Package diag provides developer/diagnostic helpers — IQ-sample decimation, energy + bandwidth estimation — that feed the web console's Constellation panel. |
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Package diversity combines IQ streams from N receivers tuned to the same frequency into a single per-sample IQ stream that's stronger and less faded than any one source.
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Package diversity combines IQ streams from N receivers tuned to the same frequency into a single per-sample IQ stream that's stronger and less faded than any one source. |
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Package equalizer implements adaptive channel equalizers used to fight simulcast distortion — the inter-symbol interference produced when multiple transmitters cover the same frequency at slightly different arrival delays at the receiver.
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Package equalizer implements adaptive channel equalizers used to fight simulcast distortion — the inter-symbol interference produced when multiple transmitters cover the same frequency at slightly different arrival delays at the receiver. |
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Package fft provides a swappable FFT abstraction.
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Package fft provides a swappable FFT abstraction. |
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Package filter implements the FIR/CIC/halfband primitives used by the DSP pipeline.
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Package filter implements the FIR/CIC/halfband primitives used by the DSP pipeline. |
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Package iqpower holds the small, reusable IQ signal-level helpers shared by the decode engines for operator-facing diagnostics: a window-averaged dBFS power measure plus the "looks dead" threshold.
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Package iqpower holds the small, reusable IQ signal-level helpers shared by the decode engines for operator-facing diagnostics: a window-averaged dBFS power measure plus the "looks dead" threshold. |
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Package loudness implements ITU-R BS.1770-4 / EBU R128 integrated loudness measurement and the gain math used for per-call loudness normalization.
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Package loudness implements ITU-R BS.1770-4 / EBU R128 integrated loudness measurement and the gain math used for per-call loudness normalization. |
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Package phase holds the small phase-domain helpers the rotation analyses use — the native Go equivalents of numpy.unwrap and the per-symbol differential phase that makes a π/4-DQPSK constellation's rotation visible.
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Package phase holds the small phase-domain helpers the rotation analyses use — the native Go equivalents of numpy.unwrap and the per-symbol differential phase that makes a π/4-DQPSK constellation's rotation visible. |
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Package spectrum produces frame-rate-limited windowed FFT magnitude frames from a stream of IQ chunks.
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Package spectrum produces frame-rate-limited windowed FFT magnitude frames from a stream of IQ chunks. |
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Package stats provides small, dependency-free numerical helpers — the descriptive statistics, histogram, mode, argmax, normalized cross-correlation and peak-finding that the signal-analysis paths reach for.
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Package stats provides small, dependency-free numerical helpers — the descriptive statistics, histogram, mode, argmax, normalized cross-correlation and peak-finding that the signal-analysis paths reach for. |
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Package sync provides symbol-time recovery and frame sync correlators.
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Package sync provides symbol-time recovery and frame sync correlators. |
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Package tuner extracts narrow-band baseband IQ for one or more frequency offsets from a single wide-band SDR IQ stream.
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Package tuner extracts narrow-band baseband IQ for one or more frequency offsets from a single wide-band SDR IQ stream. |
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Package window provides standard window functions for FIR design and FFT pre-processing.
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Package window provides standard window functions for FIR design and FFT pre-processing. |