 The natural horn can only play from a single harmonic series at a time because there is only one length of tubing available to the horn player.A proficient player can indeed alter the pitch by partially muting the bell with the right hand, thus enabling the player to reach some notes that are not part of the instrument's natural harmonic series – of course this technique also affects the quality of the tone.The player has a choice of key by using crooks to change the length of tubing.