This PR adds an M1-focused Pulse-Packet implementation for more stable transmission, and introduces a WAV-input variant in addition to .tune input. (#70)

* basic impl for M1 Mac

* Add c-apple-silicon-wav implementation

* update readme

Author: cho45

implementations/c-apple-silicon-wav/Makefile

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+CPPFLAGS=-Wall -O2
+
+main: main.c
+
+.PHONY: clean
+
+clean:
+	rm -f main

implementations/c-apple-silicon-wav/README.md

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+# c-apple-silicon-wav
+
+This is a **delta implementation** based on the Apple Silicon version in
+`implementations/c-apple-silicon`, extended to play arbitrary WAV files.
+
+For hardware assumptions and receiver setup (such as AM radio placement),
+see `implementations/c-apple-silicon/README.md`.
+This README summarizes **only the differences**.
+
+## Changes from c-apple-silicon
+
+1. Input format
+- Changed input from `.tune` to WAV
+- Run format: `./main input.wav`
+
+2. WAV loader
+- Added `RIFF/WAVE` validation
+- Scans and reads `fmt ` / `data` chunks
+- Handles chunk padding (even-byte alignment)
+- Downmixes multi-channel audio to mono
+- Applies input sample rate to playback timing
+
+3. Audio preprocessing
+- 32-bit-safe peak normalization
+- Voice-oriented pre-EQ (HP/LP + presence)
+- Compression and loudness boost via AGC + limiter
+
+4. Modulation method
+- Replaced random-sampling-based density generation with a Sigma-Delta
+  (error-accumulation) method
+- Improves intelligibility by reducing fine-grained random on/off artifacts
+
+5. Packet handling
+- Keeps sample time continuity across packets
+- Sets default `PACKET_MS` to `100ms`
+- Adjustable at runtime via `SBR_PACKET_MS`
+
+
+## Supported WAV
+
+- `RIFF/WAVE`
+- PCM 16-bit (`audio_format=1`, `bits_per_sample=16`)
+- 1 channel or more (internally downmixed to mono)
+- Any sample rate (tracked by internal timing)
+
+Not supported:
+- float PCM
+- 24/32-bit PCM
+- WAV with compressed codecs
+
+## Build
+
+```bash
+cd /Users/cho45/tmp/system-bus-radio/implementations/c-apple-silicon-wav
+make
+```
+
+## Run
+
+```bash
+./main input.wav
+```
+
+Examples:
+
+```bash
+./main hello.wav
+./main sweep.wav
+```
+
+## Main runtime parameters
+
+- `SBR_DENSITY_EXP`: Exponent of the modulation curve
+- `SBR_DENSITY_DEPTH`: Modulation depth
+- `SBR_AGC_TARGET`: Target envelope level for AGC
+- `SBR_AGC_MAKEUP`: Makeup gain after AGC
+- `SBR_AGC_MAX_GAIN`: Maximum AGC gain
+- `SBR_PACKET_MS`: Packet length (ms)
+
+## Tuning guidelines
+
+- Still too quiet: increase `SBR_AGC_TARGET`, `SBR_AGC_MAKEUP`,
+  and `SBR_AGC_MAX_GAIN`
+- Choppy output: increase `SBR_PACKET_MS` (for example `200` to `500`)
+- Distortion: decrease `SBR_AGC_MAKEUP` or `SBR_DENSITY_DEPTH`

implementations/c-apple-silicon-wav/gen_sweep.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <math.h>
+
+#define SAMPLE_RATE 24000
+#define DURATION_PER_TONE 2 
+#define NUM_TONES 5
+
+int frequencies[] = {500, 1000, 2000, 4000, 8000};
+
+int main() {
+    FILE *fp = fopen("sweep.wav", "wb");
+    if (!fp) return 1;
+    
+    uint32_t total_samples = SAMPLE_RATE * DURATION_PER_TONE * NUM_TONES;
+    uint32_t data_len = total_samples * 2;
+    uint32_t riff_len = data_len + 36;
+    
+    fwrite("RIFF", 1, 4, fp);
+    fwrite(&riff_len, 4, 1, fp);
+    fwrite("WAVE", 1, 4, fp);
+    
+    fwrite("fmt ", 1, 4, fp);
+    uint32_t fmt_len = 16;
+    uint16_t audio_fmt = 1; 
+    uint16_t num_channels = 1;
+    uint32_t sample_rate = SAMPLE_RATE;
+    uint32_t byte_rate = SAMPLE_RATE * 2;
+    uint16_t block_align = 2;
+    uint16_t bits_per_sample = 16;
+    
+    fwrite(&fmt_len, 4, 1, fp);
+    fwrite(&audio_fmt, 2, 1, fp);
+    fwrite(&num_channels, 2, 1, fp);
+    fwrite(&sample_rate, 4, 1, fp);
+    fwrite(&byte_rate, 4, 1, fp);
+    fwrite(&block_align, 2, 1, fp);
+    fwrite(&bits_per_sample, 2, 1, fp);
+    
+    fwrite("data", 1, 4, fp);
+    fwrite(&data_len, 4, 1, fp);
+    
+    for (int t = 0; t < NUM_TONES; t++) {
+        int freq = frequencies[t];
+        printf("Generating %d Hz...\n", freq);
+        for (int i = 0; i < SAMPLE_RATE * DURATION_PER_TONE; i++) {
+            double time = (double)i / SAMPLE_RATE;
+            double v = sin(2.0 * M_PI * freq * time);
+            int16_t sample = (int16_t)(v * 32000.0);
+            fwrite(&sample, 2, 1, fp);
+        }
+    }
+    
+    fclose(fp);
+    printf("Generated sweep.wav (500, 1000, 2000, 4000, 8000 Hz)\n");
+    return 0;
+}