From 1dbc86c66f60242effdf46cbac3b8394d5ba67f7 Mon Sep 17 00:00:00 2001
From: Ahmet Inan <xdsopl@gmail.com>
Date: Wed, 16 Jul 2025 12:00:49 +0200
Subject: [PATCH] use a shorter guard interval

got rid of 8k and 16k sample rates. we can resample if needed.
---
 decode.cc | 12 +++---------
 encode.cc | 16 +++++-----------
 2 files changed, 8 insertions(+), 20 deletions(-)

diff --git a/decode.cc b/decode.cc
index 8de1b91..4a441f2 100644
--- a/decode.cc
+++ b/decode.cc
@@ -37,9 +37,9 @@ struct Decoder : Common
 	typedef int16_t code_type;
 	typedef SIMD<code_type, 32> mesg_type;
 	typedef DSP::Const<value> Const;
-	static const int guard_len = rate / 100;
-	static const int symbol_len = guard_len * 16;
-	static const int filter_len = (((21 * rate) / 8000) & ~3) | 1;
+	static const int guard_len = rate / 300;
+	static const int symbol_len = guard_len * 40;
+	static const int filter_len = 129;
 	static const int extended_len = symbol_len + guard_len;
 	static const int buffer_len = 5 * extended_len;
 	static const int search_pos = extended_len;
@@ -423,12 +423,6 @@ int main(int argc, char **argv)
 	std::cerr << std::fixed << std::setprecision(1);
 	int output_count = argc - 2;
 	switch (input_file.rate()) {
-	case 8000:
-		delete new Decoder<value, cmplx, 8000>(&input_file, argv+2, output_count);
-		break;
-	case 16000:
-		delete new Decoder<value, cmplx, 16000>(&input_file, argv+2, output_count);
-		break;
 	case 44100:
 		delete new Decoder<value, cmplx, 44100>(&input_file, argv+2, output_count);
 		break;
diff --git a/encode.cc b/encode.cc
index 856c3ed..77af814 100644
--- a/encode.cc
+++ b/encode.cc
@@ -28,8 +28,8 @@ template <typename value, typename cmplx, int rate>
 struct Encoder : public Common
 {
 	typedef int8_t code_type;
-	static const int guard_len = rate / 100;
-	static const int symbol_len = guard_len * 16;
+	static const int guard_len = rate / 300;
+	static const int symbol_len = guard_len * 40;
 	DSP::WritePCM<value> *pcm;
 	DSP::FastFourierTransform<symbol_len, cmplx, -1> fwd;
 	DSP::FastFourierTransform<symbol_len, cmplx, 1> bwd;
@@ -316,8 +316,8 @@ int main(int argc, char **argv)
 	int output_chan = std::atoi(argv[4]);
 
 	int freq_off = std::atoi(argv[5]);
-	if (freq_off % 100) {
-		std::cerr << "Frequency offset must be divisible by 100." << std::endl;
+	if (freq_off % 300) {
+		std::cerr << "Frequency offset must be divisible by 300." << std::endl;
 		return 1;
 	}
 	int input_count = argc - 7;
@@ -326,7 +326,7 @@ int main(int argc, char **argv)
 		std::cerr << "Unsupported operation mode." << std::endl;
 		return 1;
 	}
-	int band_width = 2000;
+	int band_width = 2400;
 	if ((output_chan == 1 && freq_off < band_width / 2) || freq_off < band_width / 2 - output_rate / 2 || freq_off > output_rate / 2 - band_width / 2) {
 		std::cerr << "Unsupported frequency offset." << std::endl;
 		return 1;
@@ -337,12 +337,6 @@ int main(int argc, char **argv)
 	DSP::WriteWAV<value> output_file(output_name, output_rate, output_bits, output_chan);
 	output_file.silence(output_rate);
 	switch (output_rate) {
-	case 8000:
-		delete new Encoder<value, cmplx, 8000>(&output_file, argv+7, input_count, freq_off, oper_mode);
-		break;
-	case 16000:
-		delete new Encoder<value, cmplx, 16000>(&output_file, argv+7, input_count, freq_off, oper_mode);
-		break;
 	case 44100:
 		delete new Encoder<value, cmplx, 44100>(&output_file, argv+7, input_count, freq_off, oper_mode);
 		break;