Pedal tones consist of the lowest part of the trumpet's range and begin with the F below middle C. Playing these notes requires the ability to manipulate the embouchure and mouth to produce notes below the standard trumpet playing range. Some players will also use alternate fingerings and half-valves to help play these extremely low notes. Producing these notes requires the ability to vibrate the lips at an extremely slow rate of speed.
Trumpet pedal tones used to strengthen the embouchure consist of notes that fall directly below the staff. These notes must be played with closed lips. Playing with closed lips creates additional strain on the lips and helps to develop strength in the embouchure. This type of pedal tone should not be used in actual performance. It produces a very strained and unmusical timbre.
Employing a specific technique to help relax the embouchure allows the lips to buzz freely in a non-closed position. To play tones that naturally fall below the trumpet's range, you have to slow down the vibration of the lips. This will create pedal tones by manipulating the frequency of the lips and creating a vibrating massage for the lips.
The lowest pedal tones, an octave below middle C and lower, require the trumpet player to place his bottom lip outside of the mouthpiece. This technique allows the upper lip to vibrate freely. Trumpet players will play these low notes to help improve their high range and ability to "scream" on the trumpet. Screaming involves playing in the highest range while belting out notes -- a technique that requires great control.