Posted on 20 April 2015.
A440 is an international standard which states that 440 Hz is the frequency at which an A4 (the A above middle C) should be played. Before standardization, orchestral tuning varied widely across Europe. Today, A440 is a reference used by orchestras around the world.
Or is it? Many of today's professional orchestras actually tune above 440 Hz. Here is a list of alleged tuning frequencies by various professional orchestras, and here is a discussion why orchestral tuning still differs.
It's easy to find Youtube videos, mobile apps, and websites that can play a pure tone at 440 Hz. However, I had trouble finding the same thing for other common tuning frequencies. Therefore, I made pure tones for frequencies between 415 Hz and 466 Hz. Click on the buttons below for a five-second pure tone at the desired tuning frequency.