Documentation
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Index ¶
Constants ¶
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Variables ¶
This section is empty.
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 intended for tuning a recorded wideband capture's control channel down to 0 Hz before a receiver that expects a channelised, centred stream (the SDR tuner does this in the live pipeline; a file replay has to do it here).
The search is a two-stage averaged periodogram evaluated directly (a bounded Goertzel-style DFT, no full FFT): a coarse pass locates the peak bin across the band, a fine pass refines it around that bin. This costs O(nFreq · window · nWindows) — cheap for the small bounded grids used — and avoids a transform-size/zero-pad dependency.
For a suppressed-carrier linear modulation (π/4-DQPSK / LSM) the power spectral density is symmetric about the carrier, so its peak coincides with the carrier offset. Returns 0 for an empty input or zero searchHz.
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 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 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 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 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. |