PitchPerfect hears nothing on Mac

[MikeS2]

I've just tried using PitchPerfect v2.15 on my Intel iMac (Mac OS X 10.6.8). I've checked PitchPerfect's preferences and the Sound Input Device is set to Built-in Microphone.

 

I've checked System Preferences->Sound->Input and the selected input device "Name" is "Internal microphone", "Type" "Built-in". Input volume is set to full.

 

When I play my instrument, I can see the "Input level" indicator in the Sound preference pane respond and I can easily hit max indicated volume.

 

In PitchPerfect, I've tried selected "Target note" and "Target frequency" aiming at A4/440Hz.

 

PitchPerfect seems to hear nothing no matter what - "No signal" shows on its display.

 

I've tried selecting various target instruments without much hope, because I'm playing a tin whistle. Whatever settings I try, I see "No signal" regardless.

 

Can anyone suggest a possible solution? Have I missed something obvious?