For many years I've used a program called TuneIt! to tune musical instruments I build. It is also a lot of fun to use for ear training, voice control, etc. If you try it you will learn a lot about intonation with voice/whistling/instrument.
He will guide you to a free download for thirty days' trial. Even if you're not a musician it's nice to see the harmonic analysis of your voice, etc. parade across the screen.