diff --git a/src/hw/songbird.md b/src/hw/songbird.md
index 446c5e3..0fc5530 100644
--- a/src/hw/songbird.md
+++ b/src/hw/songbird.md
@@ -98,9 +98,16 @@ Note: Songbird requires an appropriate sample clock. Connect it before testing.
 
 The test generates a sine wave on each of the 4 DDS channels with a constant amplitude and different frequencies.
 
-Connect both differential outputs of DC2303-A to the oscilloscope and set these two channels to math substract.
+Connect both differential outputs of DC2303-A to the oscilloscope and set a math function to substract these two channels.
+
+If you are using the Siglent, to maximize the sample rate, use channels 1 and 3.
+
+On the oscilloscope screen, you should see a constantly shifting signal. 
+
+To fully verify the output, use the FFT function. The peaks should be at the frequencies shown by the testing tool, with some permissible harmonics later on. Below is an example of the oscilloscope screen for one Songbird connected, with DDSes generating 10, 20, 30, 40MHz.
+
+![FFT](../img/songbird_fft.png)
 
-On the oscilloscope screen, you should see a constantly shifting signal. If you use the FFT function, the peaks should be at the frequencies shown by the testing tool.
 
 ## Common issues
 
diff --git a/src/img/songbird_fft.png b/src/img/songbird_fft.png
new file mode 100644
index 0000000..ee0416e
Binary files /dev/null and b/src/img/songbird_fft.png differ