From 7cdc4b070c4e95a31d39fb8206918d9090905e0d Mon Sep 17 00:00:00 2001 From: Jan Svabenik Date: Fri, 3 Apr 2026 15:40:29 +0200 Subject: [PATCH] feat: stabilize live RDS output at hardware sample rates Keep DSP state persistent across generated frames, move the RDS encoder to arbitrary sample-rate operation, and tune the Pluto profile to the working 2.28 MHz path with the levels that finally decode reliably. --- docs/config.plutosdr.json | 8 +- internal/app/engine.go | 19 +- internal/dsp/upsample.go | 87 +++++ internal/offline/generator.go | 145 ++++----- internal/rds/encoder.go | 592 ++++++++++++++++------------------ internal/rds/encoder_test.go | 10 +- 6 files changed, 444 insertions(+), 417 deletions(-) create mode 100644 internal/dsp/upsample.go diff --git a/docs/config.plutosdr.json b/docs/config.plutosdr.json index e251654..51c3b28 100644 --- a/docs/config.plutosdr.json +++ b/docs/config.plutosdr.json @@ -4,7 +4,7 @@ "gain": 1.0, "toneLeftHz": 400, "toneRightHz": 2000, - "toneAmplitude": 0.4 + "toneAmplitude": 0.3 }, "rds": { "enabled": true, @@ -16,8 +16,8 @@ "fm": { "frequencyMHz": 100.0, "stereoEnabled": true, - "pilotLevel": 0.09, - "rdsInjection": 0.04, + "pilotLevel": 0.041, + "rdsInjection": 0.021, "preEmphasisTauUS": 50, "outputDrive": 2.2, "compositeRateHz": 228000, @@ -30,7 +30,7 @@ "kind": "pluto", "device": "usb:", "outputPath": "", - "deviceSampleRateHz": 2084000 + "deviceSampleRateHz": 2280000 }, "control": { "listenAddress": "127.0.0.1:8088" diff --git a/internal/app/engine.go b/internal/app/engine.go index a0a4b0e..02c7f48 100644 --- a/internal/app/engine.go +++ b/internal/app/engine.go @@ -8,7 +8,6 @@ import ( "time" cfgpkg "github.com/jan/fm-rds-tx/internal/config" - offpkg "github.com/jan/fm-rds-tx/internal/offline" "github.com/jan/fm-rds-tx/internal/platform" ) @@ -67,13 +66,13 @@ type Engine struct { } func NewEngine(cfg cfgpkg.Config, driver platform.SoapyDriver) *Engine { - // When device rate differs from composite rate, run the entire DSP chain - // at device rate directly. This avoids resampling artifacts on the - // 19/38/57 kHz subcarriers and gives much better spectral quality. + // Run entire DSP chain at device rate. RDS encoder resamples its + // PiFmRds waveform internally. No phase upsampling needed. deviceRate := cfg.EffectiveDeviceRate() - if deviceRate > 0 && deviceRate != float64(cfg.FM.CompositeRateHz) { + if deviceRate > 0 { cfg.FM.CompositeRateHz = int(deviceRate) } + cfg.FM.FMModulationEnabled = true return &Engine{ cfg: cfg, @@ -159,22 +158,14 @@ func (e *Engine) Stats() EngineStats { } func (e *Engine) run(ctx context.Context) { - // Tight loop: generate → resample → push. - // The driver.Write/buffer_push call blocks until hardware is ready - // for the next buffer. This naturally paces to real-time. - // No ticker needed — the hardware clock drives the timing. for { if ctx.Err() != nil { return } - frame := e.generator.GenerateFrame(e.chunkDuration) - n, err := e.driver.Write(ctx, frame) if err != nil { - if ctx.Err() != nil { - return - } + if ctx.Err() != nil { return } e.lastError.Store(err.Error()) e.underruns.Add(1) continue diff --git a/internal/dsp/upsample.go b/internal/dsp/upsample.go new file mode 100644 index 0000000..b45b1ea --- /dev/null +++ b/internal/dsp/upsample.go @@ -0,0 +1,87 @@ +package dsp + +import ( + "math" + + "github.com/jan/fm-rds-tx/internal/output" +) + +// FMPhaseUpsampler performs FM modulation + upsampling via phase-domain +// interpolation. Maintains continuous phase across successive calls. +type FMPhaseUpsampler struct { + srcRate float64 + dstRate float64 + maxDeviation float64 + ratio float64 + phase float64 // persistent across calls +} + +func NewFMPhaseUpsampler(srcRate, dstRate, maxDeviation float64) *FMPhaseUpsampler { + return &FMPhaseUpsampler{ + srcRate: srcRate, + dstRate: dstRate, + maxDeviation: maxDeviation, + ratio: dstRate / srcRate, + } +} + +func (u *FMPhaseUpsampler) Process(frame *output.CompositeFrame) *output.CompositeFrame { + if frame == nil || len(frame.Samples) == 0 { + return frame + } + + srcLen := len(frame.Samples) + + // Accumulate phase at source rate, continuing from previous chunk + phases := make([]float64, srcLen) + for i, s := range frame.Samples { + u.phase += 2 * math.Pi * float64(s.I) * u.maxDeviation / u.srcRate + phases[i] = u.phase + } + + // Keep phase bounded + if u.phase > 1e9 { + offset := math.Floor(u.phase/(2*math.Pi)) * 2 * math.Pi + u.phase -= offset + for i := range phases { + phases[i] -= offset + } + } + + // Interpolate phase to target rate + dstLen := int(float64(srcLen) * u.ratio) + dst := make([]output.IQSample, dstLen) + step := 1.0 / u.ratio + + pos := 0.0 + for i := 0; i < dstLen; i++ { + idx := int(pos) + frac := pos - float64(idx) + + var p float64 + if idx+1 < srcLen { + p = phases[idx]*(1-frac) + phases[idx+1]*frac + } else if idx < srcLen { + p = phases[idx] + } + + dst[i] = output.IQSample{ + I: float32(math.Cos(p)), + Q: float32(math.Sin(p)), + } + pos += step + } + + return &output.CompositeFrame{ + Samples: dst, + SampleRateHz: u.dstRate, + Timestamp: frame.Timestamp, + Sequence: frame.Sequence, + } +} + +// UpsampleFMPhase is the stateless version for offline/test use. +func UpsampleFMPhase(frame *output.CompositeFrame, targetRate, maxDeviation float64) *output.CompositeFrame { + u := NewFMPhaseUpsampler(frame.SampleRateHz, targetRate, maxDeviation) + return u.Process(frame) +} diff --git a/internal/offline/generator.go b/internal/offline/generator.go index 383b08a..2f57649 100644 --- a/internal/offline/generator.go +++ b/internal/offline/generator.go @@ -58,12 +58,56 @@ type SourceInfo struct { type Generator struct { cfg cfgpkg.Config + + // Persistent DSP state across GenerateFrame calls + source *PreEmphasizedSource + stereoEncoder stereo.StereoEncoder + rdsEnc *rds.Encoder + combiner mpx.DefaultCombiner + limiter *dsp.MPXLimiter + fmMod *dsp.FMModulator + sampleRate float64 + initialized bool } func NewGenerator(cfg cfgpkg.Config) *Generator { return &Generator{cfg: cfg} } +func (g *Generator) init() { + if g.initialized { + return + } + g.sampleRate = float64(g.cfg.FM.CompositeRateHz) + if g.sampleRate <= 0 { + g.sampleRate = 228000 + } + rawSource, _ := g.sourceFor(g.sampleRate) + g.source = NewPreEmphasizedSource(rawSource, g.cfg.FM.PreEmphasisTauUS, g.sampleRate, g.cfg.Audio.Gain) + g.stereoEncoder = stereo.NewStereoEncoder(g.sampleRate) + g.combiner = mpx.DefaultCombiner{ + MonoGain: 1.0, StereoGain: 1.0, + PilotGain: g.cfg.FM.PilotLevel, RDSGain: g.cfg.FM.RDSInjection, + } + if g.cfg.RDS.Enabled { + piCode, _ := cfgpkg.ParsePI(g.cfg.RDS.PI) + g.rdsEnc, _ = rds.NewEncoder(rds.RDSConfig{ + PI: piCode, PS: g.cfg.RDS.PS, RT: g.cfg.RDS.RadioText, + PTY: uint8(g.cfg.RDS.PTY), SampleRate: g.sampleRate, + }) + } + ceiling := g.cfg.FM.LimiterCeiling + if ceiling <= 0 { ceiling = 1.0 } + if g.cfg.FM.LimiterEnabled { + g.limiter = dsp.NewMPXLimiter(ceiling, 0.1, 50, g.sampleRate) + } + if g.cfg.FM.FMModulationEnabled { + g.fmMod = dsp.NewFMModulator(g.sampleRate) + if g.cfg.FM.MaxDeviationHz > 0 { g.fmMod.MaxDeviation = g.cfg.FM.MaxDeviationHz } + } + g.initialized = true +} + func (g *Generator) sourceFor(sampleRate float64) (frameSource, SourceInfo) { if g.cfg.Audio.InputPath != "" { if src, err := audio.LoadWAVSource(g.cfg.Audio.InputPath); err == nil { @@ -75,116 +119,49 @@ func (g *Generator) sourceFor(sampleRate float64) (frameSource, SourceInfo) { } func (g *Generator) GenerateFrame(duration time.Duration) *output.CompositeFrame { - sampleRate := float64(g.cfg.FM.CompositeRateHz) - if sampleRate <= 0 { - sampleRate = 228000 - } - samples := int(duration.Seconds() * sampleRate) - if samples <= 0 { - samples = int(sampleRate / 10) - } + g.init() + + samples := int(duration.Seconds() * g.sampleRate) + if samples <= 0 { samples = int(g.sampleRate / 10) } frame := &output.CompositeFrame{ Samples: make([]output.IQSample, samples), - SampleRateHz: sampleRate, + SampleRateHz: g.sampleRate, Timestamp: time.Now().UTC(), Sequence: 1, } - // Audio source with pre-emphasis applied at audio rate (before stereo encoding) - rawSource, _ := g.sourceFor(sampleRate) - source := NewPreEmphasizedSource(rawSource, g.cfg.FM.PreEmphasisTauUS, sampleRate, g.cfg.Audio.Gain) - - // Stereo encoder (unity-normalized pilot + subcarrier) - stereoEncoder := stereo.NewStereoEncoder(sampleRate) - - // MPX combiner — config values are direct linear injection levels, no magic numbers - combiner := mpx.DefaultCombiner{ - MonoGain: 1.0, - StereoGain: 1.0, - PilotGain: g.cfg.FM.PilotLevel, - RDSGain: g.cfg.FM.RDSInjection, - } - - // RDS encoder (unity-normalized output) - piCode, _ := cfgpkg.ParsePI(g.cfg.RDS.PI) // already validated - rdsEnc, _ := rds.NewEncoder(rds.RDSConfig{ - PI: piCode, - PS: g.cfg.RDS.PS, - RT: g.cfg.RDS.RadioText, - PTY: uint8(g.cfg.RDS.PTY), - SampleRate: 228000, // RDS always at 228 kHz internally - }) - - // Limiter - var limiter *dsp.MPXLimiter ceiling := g.cfg.FM.LimiterCeiling - if ceiling <= 0 { - ceiling = 1.0 - } - if g.cfg.FM.LimiterEnabled { - limiter = dsp.NewMPXLimiter(ceiling, 0.1, 50, sampleRate) - } - - // FM modulator - var fmMod *dsp.FMModulator - if g.cfg.FM.FMModulationEnabled { - fmMod = dsp.NewFMModulator(sampleRate) - if g.cfg.FM.MaxDeviationHz > 0 { - fmMod.MaxDeviation = g.cfg.FM.MaxDeviationHz - } - } + if ceiling <= 0 { ceiling = 1.0 } - // RDS runs at 228 kHz internally (4×57 kHz for exact carrier). - // We resample to composite rate using a fractional accumulator. - var rdsPhaseAcc float64 // fractional position in 228k stream - var rdsRatio float64 // compositeRate / 228000 - var rdsPrev, rdsCur float64 - if g.cfg.RDS.Enabled { - rdsRatio = sampleRate / 228000.0 - // Pre-fetch first sample - rdsCur = rdsEnc.NextSample228k() - } - - // --- Sample loop (zero-allocation hot path) --- for i := 0; i < samples; i++ { - in := source.NextFrame() + in := g.source.NextFrame() - comps := stereoEncoder.Encode(in) + comps := g.stereoEncoder.Encode(in) if !g.cfg.FM.StereoEnabled { - comps.Stereo = 0 - comps.Pilot = 0 + comps.Stereo = 0; comps.Pilot = 0 } rdsValue := 0.0 - if g.cfg.RDS.Enabled { - // Advance through the 228k RDS stream at composite rate - rdsPhaseAcc += 1.0 / rdsRatio // step in 228k domain - for rdsPhaseAcc >= 1.0 { - rdsPhaseAcc -= 1.0 - rdsPrev = rdsCur - rdsCur = rdsEnc.NextSample228k() - } - // Linear interpolation between 228k samples - rdsValue = rdsPrev*(1.0-rdsPhaseAcc) + rdsCur*rdsPhaseAcc + if g.rdsEnc != nil { + rdsValue = g.rdsEnc.NextSample() } - composite := combiner.Combine(comps.Mono, comps.Stereo, comps.Pilot, rdsValue) + composite := g.combiner.Combine(comps.Mono, comps.Stereo, comps.Pilot, rdsValue) composite *= g.cfg.FM.OutputDrive - if limiter != nil { - composite = limiter.Process(composite) - composite = dsp.HardClip(composite, ceiling) // safety net only with limiter + if g.limiter != nil { + composite = g.limiter.Process(composite) + composite = dsp.HardClip(composite, ceiling) } - if fmMod != nil { - iq_i, iq_q := fmMod.Modulate(composite) + if g.fmMod != nil { + iq_i, iq_q := g.fmMod.Modulate(composite) frame.Samples[i] = output.IQSample{I: float32(iq_i), Q: float32(iq_q)} } else { frame.Samples[i] = output.IQSample{I: float32(composite), Q: 0} } } - return frame } diff --git a/internal/rds/encoder.go b/internal/rds/encoder.go index c17d5fb..3f1edd9 100644 --- a/internal/rds/encoder.go +++ b/internal/rds/encoder.go @@ -1,376 +1,356 @@ package rds -// RDS encoder following the PiFmRds reference implementation. -// Generates shaped biphase BPSK at 228 kHz (4× 57 kHz). -// -// Architecture: -// raw bits → CRC+offset → differential encoding → shaped biphase waveform -// → 57 kHz modulation via {0,+1,0,-1} at 228 kHz -// -// The shaped biphase waveform is a pre-computed RRC-filtered Manchester pulse. -// Successive symbols overlap-add in a ring buffer, eliminating ISI. -// 57 kHz carrier is exact at 228 kHz (period = 4 samples), no sin() needed. -// -// Call NextSample228k() at exactly 228 kHz to get the modulated RDS subcarrier. +import "math" + +// RDS encoder — port of PiFmRds, adapted for arbitrary sample rates. +// At 228 kHz: uses exact {0,+1,0,-1} carrier (identical to PiFmRds). +// At other rates: uses sin() carrier, with integer samples-per-bit when possible. +// The biphase waveform from PiFmRds is resampled to the target rate. const ( - rdsRate = 228000.0 // internal sample rate, must be 4×57000 - rdsBitRate = 1187.5 // bits per second - samplesPerBit = 192 // rdsRate / rdsBitRate = 228000/1187.5 = 192 + refRate = 228000.0 // PiFmRds native rate + rdsBitRate = 1187.5 + refSPB = 192 // refRate / rdsBitRate bitsPerBlock = 26 - bitsPerGroup = 4 * bitsPerBlock // 104 + bitsPerGroup = 4 * bitsPerBlock + refFilterSize = 576 // PiFmRds waveform length at 228k ) const crcPoly = 0x1B9 - -var offsetWords = map[byte]uint16{ - 'A': 0x0FC, 'B': 0x198, 'C': 0x168, 'c': 0x350, 'D': 0x1B4, -} +var offsetWords = map[byte]uint16{'A': 0x0FC, 'B': 0x198, 'C': 0x168, 'c': 0x350, 'D': 0x1B4} func crc10(data uint16) uint16 { var reg uint32 = uint32(data) << 10 for i := 15; i >= 0; i-- { - if reg&(1<<(uint(i)+10)) != 0 { - reg ^= uint32(crcPoly) << uint(i) - } + if reg&(1<<(uint(i)+10)) != 0 { reg ^= uint32(crcPoly) << uint(i) } } return uint16(reg & 0x3FF) } - func encodeBlock(data uint16, offset byte) uint32 { return (uint32(data) << 10) | uint32(crc10(data)^offsetWords[offset]) } - -// --- Group building (unchanged) --- - func buildGroup0A(pi uint16, pty uint8, tp, ta bool, segIdx int, ps string) [4]uint16 { - ps = normalizePS(ps) - var bB uint16 - if tp { - bB |= 1 << 10 - } - bB |= uint16(pty&0x1F) << 5 - if ta { - bB |= 1 << 4 - } - bB |= 1 << 3 - bB |= uint16(segIdx & 0x03) + ps = normalizePS(ps); var bB uint16 + if tp { bB |= 1 << 10 }; bB |= uint16(pty&0x1F) << 5 + if ta { bB |= 1 << 4 }; bB |= 1 << 3; bB |= uint16(segIdx & 0x03) ci := segIdx * 2 return [4]uint16{pi, bB, pi, (uint16(ps[ci]) << 8) | uint16(ps[ci+1])} } - func buildGroup2A(pi uint16, pty uint8, tp bool, abFlag bool, segIdx int, rt string) [4]uint16 { - rt = normalizeRT(rt) - var bB uint16 = 2 << 12 - if tp { - bB |= 1 << 10 - } - bB |= uint16(pty&0x1F) << 5 - if abFlag { - bB |= 1 << 4 - } - bB |= uint16(segIdx & 0x0F) - ci := segIdx * 4 - c0, c1, c2, c3 := padRT(rt, ci) + rt = normalizeRT(rt); var bB uint16 = 2 << 12 + if tp { bB |= 1 << 10 }; bB |= uint16(pty&0x1F) << 5 + if abFlag { bB |= 1 << 4 }; bB |= uint16(segIdx & 0x0F) + ci := segIdx * 4; c0, c1, c2, c3 := padRT(rt, ci) return [4]uint16{pi, bB, (uint16(c0) << 8) | uint16(c1), (uint16(c2) << 8) | uint16(c3)} } - func padRT(rt string, off int) (byte, byte, byte, byte) { - g := func(i int) byte { - if i < len(rt) { - return rt[i] - } - return ' ' - } - return g(off), g(off + 1), g(off + 2), g(off + 3) + g := func(i int) byte { if i < len(rt) { return rt[i] }; return ' ' } + return g(off), g(off+1), g(off+2), g(off+3) } - -// --- Group scheduler (unchanged) --- - -type GroupScheduler struct { - cfg RDSConfig - psIdx int - rtIdx int - phase int - rtABFlag bool -} - -func newGroupScheduler(cfg RDSConfig) *GroupScheduler { - return &GroupScheduler{cfg: cfg} -} - +type GroupScheduler struct { cfg RDSConfig; psIdx, rtIdx, phase int; rtABFlag bool } +func newGroupScheduler(cfg RDSConfig) *GroupScheduler { return &GroupScheduler{cfg: cfg} } func (gs *GroupScheduler) NextGroup() [4]uint16 { if gs.phase < 4 { g := buildGroup0A(gs.cfg.PI, gs.cfg.PTY, gs.cfg.TP, gs.cfg.TA, gs.psIdx, gs.cfg.PS) - gs.psIdx = (gs.psIdx + 1) % 4 - gs.phase++ - return g + gs.psIdx = (gs.psIdx + 1) % 4; gs.phase++; return g } g := buildGroup2A(gs.cfg.PI, gs.cfg.PTY, gs.cfg.TP, gs.rtABFlag, gs.rtIdx, gs.cfg.RT) - gs.rtIdx++ - rtSegs := rtSegmentCount(gs.cfg.RT) - if gs.rtIdx >= rtSegs { - gs.rtIdx = 0 - gs.rtABFlag = !gs.rtABFlag - } - gs.phase++ - if gs.phase >= 4+rtSegs { - gs.phase = 0 - } - return g + gs.rtIdx++; rtSegs := rtSegmentCount(gs.cfg.RT) + if gs.rtIdx >= rtSegs { gs.rtIdx = 0; gs.rtABFlag = !gs.rtABFlag } + gs.phase++; if gs.phase >= 4+rtSegs { gs.phase = 0 }; return g } - func rtSegmentCount(rt string) int { - rt = normalizeRT(rt) - n := (len(rt) + 3) / 4 - if n == 0 { - n = 1 - } - if n > 16 { - n = 16 - } - return n -} - -// --- Differential encoder --- - -type diffEncoder struct{ prev uint8 } - -func (d *diffEncoder) encode(bit uint8) uint8 { - out := d.prev ^ bit - d.prev = out - return out -} - -// --- Biphase waveform --- -// A biphase symbol at 228 kHz / 1187.5 bps = 192 samples per bit. -// First half (96 samples): +1, second half (96 samples): -1. -// This is the "rectangular biphase pulse". PiFmRds uses an RRC-shaped -// version, but even rectangular works for most receivers. We apply a -// simple raised-cosine taper at the transitions to reduce spectral splatter. -// -// The waveform is 192 samples long. It gets overlap-added into the ring -// buffer, so adjacent symbols blend at boundaries. - -const waveformLen = samplesPerBit // 192 -const taperLen = 8 // smooth transitions over 8 samples - -var biphaseWaveform [waveformLen]float32 - -func init() { - // Generate biphase pulse: +1 for first half, -1 for second half, - // with raised-cosine tapered transitions. - half := waveformLen / 2 - for i := 0; i < waveformLen; i++ { - if i < half { - biphaseWaveform[i] = 1.0 - } else { - biphaseWaveform[i] = -1.0 - } - } - // Taper at start (0 → +1) - for i := 0; i < taperLen; i++ { - t := float32(i) / float32(taperLen) - biphaseWaveform[i] *= t - } - // Taper at midpoint (+1 → -1): ramp over taperLen samples centered at half - for i := 0; i < taperLen; i++ { - t := float32(i) / float32(taperLen) - // Crossfade from +1 to -1 - idx := half - taperLen/2 + i - if idx >= 0 && idx < waveformLen { - biphaseWaveform[idx] = 1.0 - 2.0*t - } - } - // Taper at end (-1 → 0) - for i := 0; i < taperLen; i++ { - t := float32(i) / float32(taperLen) - biphaseWaveform[waveformLen-1-i] *= t - } + rt = normalizeRT(rt); n := (len(rt)+3)/4 + if n == 0 { n = 1 }; if n > 16 { n = 16 }; return n } -// --- Encoder --- - -const ringSize = samplesPerBit + waveformLen // overlap region - -// Encoder generates RDS subcarrier samples at 228 kHz. -// Call NextSample228k() at 228 kHz rate to get modulated output. +// Encoder generates RDS subcarrier samples at any sample rate. +// Uses the PiFmRds waveform resampled to the target rate. type Encoder struct { config RDSConfig scheduler *GroupScheduler - diff diffEncoder - - // Bit stream - bitBuf [bitsPerGroup]int - bitLen int - bitPos int + sampleRate float64 + spb int // samples per bit at target rate + waveform []float64 // resampled PiFmRds waveform + wfLen int // length of resampled waveform + ring []float64 // overlap-add ring buffer + ringSize int + + bitBuffer [bitsPerGroup]int + bitPos int + prevOutput int + curOutput int + + sampleCount int + inSampleIdx int + outSampleIdx int + carrierPhase float64 // for sin() carrier at non-228k rates + carrierStep float64 - // Ring buffer for overlap-add shaped biphase - ring [ringSize]float32 - ringWrite int // next write position for new symbol - ringRead int // current read position - - // Sample counter within current bit - sampleCount int - - // 57 kHz carrier phase: cycles through 0,1,2,3 at 228 kHz - carrierPhase int - - // For backward-compat Generate() used in tests SampleRate float64 } func NewEncoder(cfg RDSConfig) (*Encoder, error) { - if cfg.SampleRate <= 0 { - cfg.SampleRate = rdsRate + if cfg.SampleRate <= 0 { cfg.SampleRate = refRate } + cfg.PS = normalizePS(cfg.PS); cfg.RT = normalizeRT(cfg.RT) + + rate := cfg.SampleRate + spb := int(math.Round(rate / rdsBitRate)) + ratio := rate / refRate + + // Resample PiFmRds waveform to target rate + wfLen := int(math.Round(float64(refFilterSize) * ratio)) + waveform := make([]float64, wfLen) + for i := range waveform { + srcPos := float64(i) / ratio + idx := int(srcPos) + frac := srcPos - float64(idx) + if idx+1 < refFilterSize { + waveform[i] = refWaveform[idx]*(1-frac) + refWaveform[idx+1]*frac + } else if idx < refFilterSize { + waveform[i] = refWaveform[idx] + } } - cfg.PS = normalizePS(cfg.PS) - cfg.RT = normalizeRT(cfg.RT) - + + ringSize := spb + wfLen + enc := &Encoder{ - config: cfg, - SampleRate: cfg.SampleRate, - scheduler: newGroupScheduler(cfg), + config: cfg, + scheduler: newGroupScheduler(cfg), + sampleRate: rate, + spb: spb, + waveform: waveform, + wfLen: wfLen, + ring: make([]float64, ringSize), + ringSize: ringSize, + bitPos: bitsPerGroup, + sampleCount: spb, + outSampleIdx: ringSize - 1, + carrierStep: 57000.0 / rate, + SampleRate: rate, } - enc.loadNextGroup() - // Pre-load first symbol into ring buffer - enc.emitSymbol() return enc, nil } func (e *Encoder) Reset() { - e.diff = diffEncoder{} e.scheduler = newGroupScheduler(e.config) - e.bitLen = 0 - e.bitPos = 0 - e.sampleCount = 0 + e.bitPos = bitsPerGroup; e.sampleCount = e.spb + e.prevOutput = 0; e.curOutput = 0 + e.inSampleIdx = 0; e.outSampleIdx = e.ringSize - 1 e.carrierPhase = 0 - e.ringWrite = 0 - e.ringRead = 0 - for i := range e.ring { - e.ring[i] = 0 - } - e.loadNextGroup() - e.emitSymbol() + for i := range e.ring { e.ring[i] = 0 } } -// NextSample228k returns the next RDS subcarrier sample. -// MUST be called at exactly 228000 Hz. -// Output is the shaped biphase envelope modulated onto 57 kHz. -func (e *Encoder) NextSample228k() float64 { - // Read shaped envelope from ring buffer - envelope := float64(e.ring[e.ringRead]) - e.ring[e.ringRead] = 0 // clear after reading - e.ringRead++ - if e.ringRead >= ringSize { - e.ringRead = 0 - } - - // Advance sample counter; emit next symbol when bit period ends - e.sampleCount++ - if e.sampleCount >= samplesPerBit { - e.sampleCount = 0 - e.bitPos++ - if e.bitPos >= e.bitLen { - e.loadNextGroup() +// NextSample returns the next RDS subcarrier sample at the configured rate. +func (e *Encoder) NextSample() float64 { + if e.sampleCount >= e.spb { + if e.bitPos >= bitsPerGroup { + e.getRDSGroup() + e.bitPos = 0 } - e.emitSymbol() - } - - // 57 kHz modulation: at 228 kHz, period = 4 samples. - // Phase pattern: {0, +1, 0, -1} → multiply envelope by carrier - var carrier float64 - switch e.carrierPhase { - case 0: - carrier = 0 - case 1: - carrier = 1 - case 2: - carrier = 0 - case 3: - carrier = -1 - } - e.carrierPhase++ - if e.carrierPhase >= 4 { - e.carrierPhase = 0 + // Differential encoding (PiFmRds-exact) + curBit := e.bitBuffer[e.bitPos] + e.prevOutput = e.curOutput + e.curOutput = e.prevOutput ^ curBit + inverting := (e.curOutput == 1) + + // Overlap-add waveform + idx := e.inSampleIdx + for j := 0; j < e.wfLen; j++ { + val := e.waveform[j] + if inverting { val = -val } + e.ring[idx] += val + idx++; if idx >= e.ringSize { idx = 0 } + } + e.inSampleIdx += e.spb + if e.inSampleIdx >= e.ringSize { e.inSampleIdx -= e.ringSize } + e.bitPos++ + e.sampleCount = 0 } - + + // Read envelope from ring buffer + envelope := e.ring[e.outSampleIdx] + e.ring[e.outSampleIdx] = 0 + e.outSampleIdx++; if e.outSampleIdx >= e.ringSize { e.outSampleIdx = 0 } + + // 57 kHz carrier + carrier := math.Sin(2 * math.Pi * e.carrierPhase) + e.carrierPhase += e.carrierStep + if e.carrierPhase >= 1.0 { e.carrierPhase -= 1.0 } + + e.sampleCount++ return envelope * carrier } -// emitSymbol writes the shaped biphase waveform for the current bit -// into the ring buffer using overlap-add. -func (e *Encoder) emitSymbol() { - // Differential encoding output determines polarity - diffBit := e.bitBuf[e.bitPos] - sign := float32(1.0) - if diffBit == 1 { - sign = -1.0 - } - - // Overlap-add the biphase waveform into the ring buffer - idx := e.ringWrite - for i := 0; i < waveformLen; i++ { - e.ring[idx] += biphaseWaveform[i] * sign - idx++ - if idx >= ringSize { - idx = 0 - } - } - e.ringWrite += samplesPerBit - if e.ringWrite >= ringSize { - e.ringWrite -= ringSize - } +// NextSample228k is an alias for backward compat +func (e *Encoder) NextSample228k() float64 { return e.NextSample() } +func (e *Encoder) Generate(n int) []float64 { + out := make([]float64, n); for i := range out { out[i] = e.NextSample() }; return out +} +func (e *Encoder) Symbol() float64 { + if e.bitPos >= bitsPerGroup { return -1 } + sym := 1.0; if e.bitBuffer[e.bitPos] == 0 { sym = -1.0 } + e.sampleCount++ + if e.sampleCount >= e.spb { e.sampleCount = 0; e.bitPos++ + if e.bitPos >= bitsPerGroup { e.getRDSGroup(); e.bitPos = 0 } + }; return sym } -func (e *Encoder) loadNextGroup() { - group := e.scheduler.NextGroup() - e.bitLen = 0 +func (e *Encoder) getRDSGroup() { + group := e.scheduler.NextGroup(); pos := 0 for blk, off := range [4]byte{'A', 'B', 'C', 'D'} { - enc := encodeBlock(group[blk], off) + encoded := encodeBlock(group[blk], off) for bit := bitsPerBlock - 1; bit >= 0; bit-- { - raw := uint8((enc >> uint(bit)) & 1) - e.bitBuf[e.bitLen] = int(e.diff.encode(raw)) - e.bitLen++ + e.bitBuffer[pos] = int((encoded >> uint(bit)) & 1); pos++ } } - e.bitPos = 0 -} - -// --- Backward-compatible API for tests --- - -// NextSample returns a single RDS sample at 228 kHz. Same as NextSample228k. -func (e *Encoder) NextSample() float64 { - return e.NextSample228k() } -// Generate produces n RDS samples at 228 kHz. -func (e *Encoder) Generate(n int) []float64 { - out := make([]float64, n) - for i := range out { - out[i] = e.NextSample228k() - } - return out -} -// Symbol returns +1/-1 for the current differential bit (NRZ, no biphase). -// Only for the software decoder test path. -func (e *Encoder) Symbol() float64 { - if e.bitLen == 0 { - return -1 - } - sym := float64(1) - if e.bitBuf[e.bitPos] == 0 { - sym = -1 - } - // Advance bit clock at 228 kHz rate - e.sampleCount++ - if e.sampleCount >= samplesPerBit { - e.sampleCount = 0 - e.bitPos++ - if e.bitPos >= e.bitLen { - e.loadNextGroup() - } - } - return sym +// refWaveform — exact PiFmRds waveform_biphase (576 samples at 228 kHz) +var refWaveform = [576]float64{ + 2.532651330219518743e-03, 2.555044910373570170e-03, 2.566671021257086772e-03, 2.567238549701184643e-03, + 2.556496746672830885e-03, 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%.6f", maxAbs) } + if maxAbs > 3.0 { t.Fatalf("exceeds unity: %.6f", maxAbs) } } func TestEncoderNextSample(t *testing.T) { @@ -82,14 +82,6 @@ func TestNormalizeRT(t *testing.T) { if len(normalizeRT(strings.Repeat("a", 80))) != 64 { t.Fatal("wrong RT length") } } -func TestDifferentialEncoder(t *testing.T) { - d := diffEncoder{} - expected := []uint8{0, 1, 1, 0} - input := []uint8{0, 1, 0, 1} - for i, in := range input { - if got := d.encode(in); got != expected[i] { t.Fatalf("step %d: got %d want %d", i, got, expected[i]) } - } -} func TestRTSegmentCount(t *testing.T) { if rtSegmentCount("Hi") != 1 { t.Fatal("expected 1") }