1 files changed, 114 insertions, 0 deletions
diff --git a/src/client/kotlin/space/autistic/radio/client/fmsim/FmFullConstants.kt b/src/client/kotlin/space/autistic/radio/client/fmsim/FmFullConstants.kt
new file mode 100644
index 0000000..f5a49ce
--- /dev/null
+++ b/src/client/kotlin/space/autistic/radio/client/fmsim/FmFullConstants.kt
@@ -0,0 +1,114 @@
+package space.autistic.radio.client.fmsim
+
+import kotlin.math.PI
+import kotlin.math.cos
+import kotlin.math.sin
+
+object FmFullConstants {
+    // tau = 75us, fh = 20396.25Hz
+    const val FM_PREEMPAHSIS_B0_48K = 6.7639647f
+    const val FM_PREEMPHASIS_B1_48K = -4.975628f
+
+    /* const val FM_PREEMPHASIS_A0_48K = 1f */
+    const val FM_PREEMPHASIS_A1_48K = 0.78833646f
+
+    const val FM_DEEMPAHSIS_B0_48K = 1f / FM_PREEMPAHSIS_B0_48K
+    const val FM_DEEMPHASIS_B1_48K = FM_PREEMPHASIS_A1_48K / FM_PREEMPAHSIS_B0_48K
+
+    /* const val FM_DEEMPHASIS_A0_48K = 1f */
+    const val FM_DEEMPHASIS_A1_48K = FM_PREEMPHASIS_B1_48K / FM_PREEMPAHSIS_B0_48K
+
+    val FIR_LPF_48K_15K_3K1 = floatArrayOf(
+        -0.0010006913216784596f,
+        0.001505308784544468f,
+        -2.625857350794219e-18f,
+        -0.002777613466605544f,
+        0.0030173989944159985f,
+        0.002290070755407214f,
+        -0.008225799538195133f,
+        0.004239063244313002f,
+        0.010359899140894413f,
+        -0.017650796100497246f,
+        1.510757873119297e-17f,
+        0.029305754229426384f,
+        -0.02889496460556984f,
+        -0.020366130396723747f,
+        0.07103750854730606f,
+        -0.03811456635594368f,
+        -0.10945471376180649f,
+        0.29212409257888794f,
+        0.6252123713493347f,
+        0.29212409257888794f,
+        -0.10945471376180649f,
+        -0.03811456635594368f,
+        0.07103750854730606f,
+        -0.020366130396723747f,
+        -0.02889496460556984f,
+        0.029305754229426384f,
+        1.510757873119297e-17f,
+        -0.017650796100497246f,
+        0.010359899140894413f,
+        0.004239063244313002f,
+        -0.008225799538195133f,
+        0.002290070755407214f,
+        0.0030173989944159985f,
+        -0.002777613466605544f,
+        -2.625857350794219e-18f,
+        0.001505308784544468f,
+        -0.0010006913216784596f,
+    )
+
+    // chosen such that we can easily do 38kHz mixing in frequency (1500*38k/300k = shift of 95 bins, where 1500 comes
+    // from the 4/25 ratio 48k/300k i.e. 240*25/4)
+    // (the theoretical optimum, as per above, would be around 180)
+    // (we could have fudged the carrier frequency a bit but we chose not to)
+    // NOTE: latency = (data block size / 48000) seconds (84 -> 1.75 ms)
+    const val FFT_SIZE_LPF_48K_15K_3K1 = 2 * 120
+    const val FFT_OVERLAP_LPF_48K_15K_3K1 = 36
+    const val FFT_DATA_BLOCK_SIZE_LPF_48K_15K_3K1 = FFT_SIZE_LPF_48K_15K_3K1 - FFT_OVERLAP_LPF_48K_15K_3K1
+
+    init {
+        assert(FFT_OVERLAP_LPF_48K_15K_3K1 >= FIR_LPF_48K_15K_3K1.size - 1)
+    }
+
+    const val DECIMATION_48K_300K = 4
+    const val INTERPOLATION_48K_300K = 25
+
+    const val FFT_SIZE_48K_300K = FFT_SIZE_LPF_48K_15K_3K1 * INTERPOLATION_48K_300K / DECIMATION_48K_300K
+    const val FFT_OVERLAP_48K_300K = FFT_OVERLAP_LPF_48K_15K_3K1 * INTERPOLATION_48K_300K / DECIMATION_48K_300K
+    const val FFT_DATA_BLOCK_SIZE_48K_300K = FFT_SIZE_48K_300K - FFT_OVERLAP_48K_300K
+
+    // how many bins to shift for 38kHz mixing
+    // assuming FFT_SIZE_LPF_48K_15K_3K1 *bins* (complex)
+    // 19 / 150 is the ratio between 38k/300k
+    const val FREQUENCY_MIXING_BINS_38K =
+        FFT_SIZE_LPF_48K_15K_3K1 * INTERPOLATION_48K_300K / DECIMATION_48K_300K * 19 / 150
+
+    // a single cycle of a 19kHz signal takes (1/19k)/(1/300k) or 300k/19k samples.
+    // since that number isn't exact, buffer an entire 19 cycles.
+    const val BUFFER_SIZE_19K_300K = 300
+
+    // using cosine is nicer
+    val BUFFER_19K_300K = FloatArray(BUFFER_SIZE_19K_300K) {
+        0.1f * cos(2 * PI * 19000.0 * it.toDouble() / 300000.0).toFloat()
+    }
+
+    // we want a carrier deviation of +-75kHz, at a sampling rate of 300kHz
+    const val CORRECTION_FACTOR = (75000.0 / (300000.0 / (2.0 * PI))).toFloat()
+    const val INVERSE_CORRECTION_FACTOR = 1 / CORRECTION_FACTOR
+
+    // these are used for "low/high" mixing
+    const val CBUFFER_SIZE_100K_300K = 3
+
+    val CBUFFER_100K_300K = FloatArray(2 * CBUFFER_SIZE_100K_300K) {
+        val index = it / 2
+        if (it and 1 == 0) {
+            1f * sin(2 * PI * 100000.0 * index.toDouble() / 300000.0).toFloat()
+        } else {
+            1f * cos(2 * PI * 100000.0 * index.toDouble() / 300000.0).toFloat()
+        }
+    }
+
+    const val STEREO = true
+    const val MONO = false
+}
\ No newline at end of file