diff --git a/src/daq/record.rs b/src/daq/record.rs
index 9cafaba..86f2daf 100644
--- a/src/daq/record.rs
+++ b/src/daq/record.rs
@@ -76,7 +76,7 @@ impl RecordSettings {
 /// This struct lets a recording run on a stream, waits till the first data arrives and records for a given period of time. Usage:
 ///
 /// ```
-/// use lasprs::{RecordSettings, StreamMgr, Recording};
+/// use lasprs::daq::{RecordSettings, StreamMgr, Recording};
 /// use std::time::Duration;
 ///
 /// fn main() -> anyhow::Result<()> {
diff --git a/src/ps/aps.rs b/src/ps/aps.rs
index b7b3f77..427c3fb 100644
--- a/src/ps/aps.rs
+++ b/src/ps/aps.rs
@@ -427,18 +427,46 @@ mod test {
             assert!(false);
         }
     }
+
+    #[test]
+    fn test_tf2() {
+        let nfft = 4800;
+        let distr = Normal::new(1.0, 1.0).unwrap();
+        let mut timedata = Dmat::random((nfft, 1), distr);
+        timedata
+            .push_column(timedata.column(0).mapv(|a| 2. * a).view())
+            .unwrap();
+        // Negative reference channel
+        timedata
+            .push_column(timedata.column(0).mapv(|a| -1. * a).view())
+            .unwrap();
+
+        let mut aps = AvPowerSpectra::build(nfft, None, None, None).unwrap();
+        if let ApsResult::OnlyLastResult(v) = aps.compute_last(&timedata) {
+            let tf = v.tf(0, 1, Some(2));
+            assert_eq!((&tf - 2.0 * Cflt::ONE).sum().abs(), 0.0);
+        } else {
+            assert!(false);
+        }
+    }
     #[test]
     fn test_ap() {
         let nfft = 256;
         let distr = Normal::new(1.0, 1.0).unwrap();
-        let timedata = Dmat::random((500 * nfft, 1), distr);
+        let timedata = Dmat::random((100 * nfft, 1), distr);
         let timedata_mean_square = (&timedata * &timedata).sum() / (timedata.len() as Flt);
 
-        for wt in [Some(WindowType::Rect), Some(WindowType::Hann), Some(WindowType::Bartlett), Some(WindowType::Blackman), None] {
+        for wt in [
+            Some(WindowType::Rect),
+            Some(WindowType::Hann),
+            Some(WindowType::Bartlett),
+            Some(WindowType::Blackman),
+            None,
+        ] {
             let mut aps = AvPowerSpectra::build(nfft, wt, None, None).unwrap();
             if let ApsResult::OnlyLastResult(v) = aps.compute_last(&timedata) {
                 let ap = v.ap(0);
-                assert_abs_diff_eq!((&ap).sum().abs(), timedata_mean_square, epsilon = 4e-3);
+                assert_abs_diff_eq!((&ap).sum().abs(), timedata_mean_square, epsilon = 8e-3);
             } else {
                 assert!(false);
             }