switch to mask decoder. Seems to work much better

src/codec2/mod.rs

@@ -5,7 +5,7 @@ use std::{
 
 const MODE_M_MAX: usize = 4;
 const M: i32 = 2;
-const N_SYM: i32 = 35;
+const N_SYM: i32 = 50;
 
 #[link(name = "fsk", kind = "static")]
 extern "C" {
@@ -33,6 +33,8 @@ extern "C" {
     );
 
     fn fsk_set_freq_est_limits(fsk: *mut InternalFsk, f_min: libc::c_int, f_max: libc::c_int);
+
+    fn fsk_set_freq_est_alg(fsk: *mut InternalFsk, est_type: libc::c_int);
 }
 
 #[repr(C)]
@@ -147,14 +149,17 @@ impl<I: Iterator<Item = Complex>> Fsk<I> {
         const P: i32 = 5;
         const FS: i32 = 9600 * P;
 
-        let internal = unsafe { fsk_create_hbr(FS, 9600, M, P, N_SYM, -1, 0) };
+        let internal = unsafe { fsk_create_hbr(FS, 9600, M, P, N_SYM, -1, 9600) };
 
         // Set upper/lower bound on the FSK peaks, from center
         // (Hz)
-        let fsk_lower = -10_000;
-        let fsk_upper = 10_000;
+        let fsk_lower = -15_000;
+        let fsk_upper = 15_000;
 
-        unsafe { fsk_set_freq_est_limits(internal, fsk_lower, fsk_upper) };
+        unsafe {
+            fsk_set_freq_est_limits(internal, fsk_lower, fsk_upper);
+            fsk_set_freq_est_alg(internal, 1); // mask estimator
+        }
 
         Self {
             internal,