The flanger extends the phasing effect also adding a pitch shifter [Pitch Shifter ] , in other words, a circuit capable of increasing or decreasing the signal's tonality (the classic pitch shifting example is when you accelerate or decelerate the roll of a magnetic ribbon). To give a practical explanation of this phenomenon let's consider (as usual) a sinusoid at a certain frequency-level recorded on a magnetic ribbon. By increasing the ribbon's speed we'll see that the sinusoid gets reproduced more quickly, which basically means that sinusoid with a higher frequency gets generated. The logical scheme is the following (in its early days, this effect was also created by using an analogue-reel recorder):

We can see how the LFO pilots both the delay module and the pitch shifter module.
The following is a sound to which a Flanger effect has been applied.




Flanger