There are eight Doppler Effect Formulas for frequency depending on cases:

(i) When the source is moving towards a observer at rest
                                     
(ii) When the source is moving away from the observer at rest
                                  
(iii) When observer is moving towards the stationary source
                                  
(iv) When observer moving away from a stationary source
                                  
(v) When both Source and observer moves towards each other
                                  

(vi) When both Source and observer move away from each other
                                  
(Vii) When the Source is approaching the Stationary observer and observer moving away from it
                                   
(Viii) When the Observer is approaching the Stationary source and source moving away from it
                                   

Where, v_s = Velocity of the Source,
v_o = Velocity of the Observer,
v = Velocity of sound or light in medium,
f = Real frequency,
f’ = Apparent frequency.