Sing a note into your tape recorder. Hold the sound for five to 10 seconds to make sure you record it.
Play the recorder back to hear the note. Determine if it is a high or low pitch to help you narrow down the matching sound on the piano. A low pitch will be on the left half of the keyboard, while higher pitches will be located on the right half of the keyboard.
Play two keys on the piano, one that sounds higher than your recorded tone and one that sounds lower. Keep doing this until you have narrowed down the possible notes on the keyboard you were trying to match with your voice.